==================

Frequently executed functions in programs are some times compiled
into different versions to take advantage of some specific
advanced features present in some of the types of platforms on
which the program is executed. For instance, SSE4 versus no-SSE4.
Existing techniques to do multi-versioning, for example using
indirect calls, block compiler optimizations, mainly inlining.

This patch adds a new GCC pass to support multi-versioned calls
through a new builtin, __builtin_dispatch.  The __builtin_dispatch
call is converted into a simple if-then construct to call the
appropriate version at run-time. There are no indirect calls so
inlining is not affected.

This patch also supports a function unswitching optimization via
cloning of functions, only along hot paths, that call multi-versioned
functions so that the hot multi-versioned paths can be independently
optimized for performance. The cloning optimization is switched on
via a flag, -fclone-hot-version-paths. 

Only two versions are supported in this patch. Example use :

  int popcnt_sse4(unsigned int x) __attribute__((__target__("popcnt")));
  int popcnt_sse4(unsigned int x)
  {
    int count = __builtin_popcount(x);
    return count;
  }

  int popcnt(unsigned int x) __attribute__((__target__("no-popcnt")));
  int popcnt(unsigned int x)
  {
    int count = __builtin_popcount(x);
    return count;
  }

  int testsse() __attribute__((version_selector));
  int main ()
  {
    ...
    /* The multi-versioned call. */
    ret = __builtin_dispatch (testsse,  (void*)popcnt_sse4, (void*)popcnt, 25);
    ...
  }

  There are two passes that are run to achieve multi-versioning.
  "pass_ipa_multiversion_dispatch" is an ipa pass that decides which functions
  have to be cloned and hoists the feature-test calls appropriately.  This
  pass can be enabled with the flag "-fclone-hot-version-paths" and disabled
  with "-fno-clone-hot-version-paths".

  "pass_tree_convert_builtin_dispatch" does the lowering.  It is a
  function-level pass.  Functions marked with attribute "version_selector" are
  also handled by this pass.  This pass is always on.

  How to use __builtin_dispatch ?
  -----------------------------

  __builtin_dispatch takes 3 mandatory arguments :

  __builtin_dispatch (arg1, arg2, arg3, <arg4>, <arg5>, ...);

  arg1 is the pointer to the feature-test function, the outcome of this
  function decides the version that must be executed.
  arg2 is the ( void *) cast pointer to the versioned function that is
  executed when the feature test returns 1.
  arg3 is the ( void *) cast pointer to the versioned function that is
  executed when the feature test returns 0.
  arg4, arg5, ... are optional. They are the arguments to the versioned
  functions.  Both versions must accept the same number of arguments.
  The __builtin_dispatch function returns the value returned by the
  versioned function that gets executed.  The versioned function arg2
  is executed when the feature_test function arg1 returns 1 and arg3
  is executed when the feature_test function arg1 returns 0. arg1
  could be marked as a "version_selector" function if it is a pure
  function with no side-effects, returns a constant at run-time and
  can be evaluated at any point in the execution.

  When to use the "version_selector" attribute ?
  -----------------------------------------------

  Functions are marked with attribute "version_selector" only if
  they are run-time constants.  Example of such functions would
  be those that test if a specific feature is available on a
  particular architecture.  Such functions must return a positive
  integer. For two-way functions, those that test if a feature
  is present or not must return 1 or 0 respectively.

  This patch will make constructors that call these function once
  and assign the outcome to a global variable. From then on, only
  the value of the global will be used to decide which version to
  execute.

  What happens with cloning, -fclone-hot-version-paths ?
  -----------------------------------------------------

  For the call graph that looks like this before cloning :

func_cold ----> func_hot ----> findOnes ----> IsPopCntSupported ----> popcnt
                                                |
                                                -----> no_popcnt

  where popcnt and no_popcnt are the multi-versioned functions, then after cloning :

func_cold ---->IsPopCntSupported ----> func_hot_clone0 ----> findOnes_clone0 ----> popcnt
                              |
                               ----> func_hot_clone1 ----> findOnes_clone1 ----> no_popcnt

     

 
  Flags : -fclone-hot-version-paths does function unswitching via cloning.
          --param=num-mversn-clones=<num> allows to specify the number of
          functions that should be cloned.
	  --param=mversn-clone-depth=<num> allows to specify the length of
          the call graph path that should be cloned.  num = 0 implies only
          leaf node that contains the __builtin_dispatch statement must be
          cloned.
============================================================================================

Google ref 45947, 45986

2011-04-28  Sriraman Tallam  <tmsriram@google.com>

	* c-family/c-common.c	(revision 173122) (handle_version_selector_attribute): New function.
	(c_common_attribute_table): New attribute "version_selector".
	* tree-pass.h	(revision 173122) (pass_tree_convert_builtin_dispatch): New pass.
	(pass_ipa_multiversion_dispatch): New pass.
	* testsuite/gcc.dg/mversn7.c	(revision 0): New test case.
	* testsuite/gcc.dg/mversn4.c	(revision 0): New test case.
	* testsuite/gcc.dg/mversn4.h	(revision 0): New test case.
	* testsuite/gcc.dg/mversn4a.c	(revision 0): New test case.
	* testsuite/gcc.dg/torture/mversn1.c	(revision 0): New test case.
	* testsuite/gcc.dg/mversn2.c	(revision 0): New test case.
	* testsuite/gcc.dg/mversn6.c	(revision 0): New test case.
	* testsuite/gcc.dg/mversn3.c	(revision 0): New test case.
	* testsuite/g++.dg/mversn8.C	(revision 0): New test case.
	* testsuite/g++.dg/mversn10a.C	(revision 0): New test case.
	* testsuite/g++.dg/mversn14a.C	(revision 0): New test case.
	* testsuite/g++.dg/tree-prof/mversn13.C	(revision 0): New test case.
	* testsuite/g++.dg/tree-prof/mversn15.C	(revision 0): New test case.
	* testsuite/g++.dg/tree-prof/mversn15a.C	(revision 0): New test case.
	* testsuite/g++.dg/mversn9.C	(revision 0): New test case.
	* testsuite/g++.dg/mversn10.C	(revision 0): New test case.
	* testsuite/g++.dg/mversn12.C	(revision 0): New test case.
	* testsuite/g++.dg/mversn14.C	(revision 0): New test case.
	* testsuite/g++.dg/mversn16.C	(revision 0): New test case.
	* testsuite/g++.dg/torture/mversn11.C	(revision 0): New test case.
	* testsuite/g++.dg/torture/mversn5.C	(revision 0): New test case.
	* testsuite/g++.dg/torture/mversn5.h	(revision 0): New test case.
	* testsuite/g++.dg/torture/mversn5a.C	(revision 0): New test case.
	* builtin-types.def	(revision 173122) (BT_PTR_FN_INT): New pointer type.
	(BT_FN_INT_PTR_FN_INT_PTR_PTR_VAR): New function type for __builtin_dispatch.
	* builtins.def	(revision 173122) (BUILT_IN_DISPATCH): New builtin to
	support multi-version calls.
	* mversn-dispatch.c	(revision 0): New file.
	* timevar.def	(revision 173122) (TV_MVERSN_DISPATCH): New time var.
	* common.opt	(revision 173122) (fclone-hot-version-paths): New flag.
	* Makefile.in	(revision 173122) (mversn-dispatch.o): New rule.
	* passes.c	(revision 173122) (init_optimization_passes): Add the new
	multi-version and dispatch passes to the pass list.
	* params.def	(revision 173122) (PARAM_NUMBER_OF_MVERSN_CLONES): Define.
	(PARAM_MVERSN_CLONE_CGRAPH_DEPTH): Define.
	* doc/invoke.texi	(revision 173122) (mversn-clone-depth): Document.
	(num-mversn-clones): Document.
	(fclone-hot-version-paths): Document.

Index: doc/invoke.texi
===================================================================
--- doc/invoke.texi	(revision 173122)
+++ doc/invoke.texi	(working copy)
@@ -342,7 +342,8 @@
 -falign-labels[=@var{n}] -falign-loops[=@var{n}] -fassociative-math @gol
 -fauto-inc-dec -fbranch-probabilities -fbranch-target-load-optimize @gol
 -fbranch-target-load-optimize2 -fbtr-bb-exclusive -fcaller-saves @gol
--fcheck-data-deps -fcombine-stack-adjustments -fconserve-stack @gol
+-fcheck-data-deps -fclone-hot-version-paths @gol
+-fcombine-stack-adjustments -fconserve-stack @gol
 -fcompare-elim -fcprop-registers -fcrossjumping @gol
 -fcse-follow-jumps -fcse-skip-blocks -fcx-fortran-rules @gol
 -fcx-limited-range @gol
@@ -8229,6 +8230,10 @@
 branch is most likely to take, the @samp{REG_BR_PROB} values are used to
 exactly determine which path is taken more often.
 
+@item -fclone-hot-version-paths
+When multi-version calls are made using @samp{__builtin_dispatch}, this flag
+enables cloning and hoisting of hot multiversioned paths.
+
 @item -fprofile-values
 @opindex fprofile-values
 If combined with @option{-fprofile-arcs}, it adds code so that some
@@ -8490,6 +8495,16 @@
 be applied.
 The default value is 40.
 
+@item mversn-clone-depth
+When using @option{-fclone-hot-version-paths}, hot function paths are multi-
+versioned via cloning.  This parameter specifies the maximum length of the
+call graph path that can be cloned. The default value is 2.
+
+@item num-mversn-clones
+When using @option{-fclone-hot-version-paths}, hot function paths are multi-
+versioned via cloning.  This parameter specifies the maximum number of
+functions that can be cloned. The default value is 10.
+
 @item large-function-insns
 The limit specifying really large functions.  For functions larger than this
 limit after inlining, inlining is constrained by
Index: c-family/c-common.c
===================================================================
--- c-family/c-common.c	(revision 173122)
+++ c-family/c-common.c	(working copy)
@@ -315,6 +315,7 @@ static tree check_case_value (tree);
 static bool check_case_bounds (tree, tree, tree *, tree *);
 
 static tree handle_packed_attribute (tree *, tree, tree, int, bool *);
+static tree handle_version_selector_attribute (tree *, tree, tree, int, bool *);
 static tree handle_nocommon_attribute (tree *, tree, tree, int, bool *);
 static tree handle_common_attribute (tree *, tree, tree, int, bool *);
 static tree handle_noreturn_attribute (tree *, tree, tree, int, bool *);
@@ -603,6 +604,8 @@ const unsigned int num_c_common_reswords =
 const struct attribute_spec c_common_attribute_table[] =
 {
   /* { name, min_len, max_len, decl_req, type_req, fn_type_req, handler } */
+  { "version_selector",	      0, 0, true, false, false,
+			      handle_version_selector_attribute },
   { "packed",                 0, 0, false, false, false,
 			      handle_packed_attribute },
   { "nocommon",               0, 0, true,  false, false,
@@ -5782,6 +5785,37 @@ handle_packed_attribute (tree *node, tree name, tr
   return NULL_TREE;
 }
 
+/* Handle a "version_selector attribute".
+   Functions are marked with attribute "version_selector" only if
+   they are run-time constants.  Example of such functions would
+   be those that test if a particular feature is available on a
+   particular architecture.  Such function must return a positive
+   integer. For two-way functions, those that test if a feature
+   is present or not must return 1 or 0 respectively. */
+
+static tree
+handle_version_selector_attribute (tree *node, tree name,
+ 				   tree ARG_UNUSED (args),
+ 				   int ARG_UNUSED (flags),
+				   bool *no_add_attrs)
+{
+  if (TREE_CODE (*node) == FUNCTION_DECL)
+    {
+      /* Check that the return type is integer. */
+      gcc_assert (TREE_CODE (TREE_TYPE (TREE_TYPE (*node)))
+                  == INTEGER_TYPE);
+      if (dump_file)
+        fprintf (dump_file, "%s is a version_selector function\n",
+   	         IDENTIFIER_POINTER (DECL_NAME (*node)));
+    }
+  else
+    {
+      warning (OPT_Wattributes, "%qE attribute ignored", name);
+      *no_add_attrs = true;
+    }
+  return NULL_TREE;
+}
+
 /* Handle a "nocommon" attribute; arguments as in
    struct attribute_spec.handler.  */
 
Index: tree-pass.h
===================================================================
--- tree-pass.h	(revision 173122)
+++ tree-pass.h	(working copy)
@@ -448,6 +448,7 @@ extern struct gimple_opt_pass pass_warn_unused_res
 extern struct gimple_opt_pass pass_split_functions;
 extern struct gimple_opt_pass pass_feedback_split_functions;
 extern struct gimple_opt_pass pass_threadsafe_analyze;
+extern struct gimple_opt_pass pass_tree_convert_builtin_dispatch;
 
 /* IPA Passes */
 extern struct simple_ipa_opt_pass pass_ipa_lower_emutls;
@@ -472,6 +473,7 @@ extern struct ipa_opt_pass_d pass_ipa_lto_wpa_fixu
 extern struct ipa_opt_pass_d pass_ipa_lto_finish_out;
 extern struct ipa_opt_pass_d pass_ipa_profile;
 extern struct ipa_opt_pass_d pass_ipa_cdtor_merge;
+extern struct simple_ipa_opt_pass pass_ipa_multiversion_dispatch;
 
 extern struct gimple_opt_pass pass_all_optimizations;
 extern struct gimple_opt_pass pass_cleanup_cfg_post_optimizing;
Index: testsuite/gcc.dg/mversn7.c
===================================================================
--- testsuite/gcc.dg/mversn7.c	(revision 0)
+++ testsuite/gcc.dg/mversn7.c	(revision 0)
@@ -0,0 +1,47 @@
+/* This test checks if cloning and dispatching works correctly with
+   a motivating example. The function problem calculates the sum of
+   numbers from 1 to 10 in two different ways.  Hence, after cloning
+   both clones should return 55, which means main returns 0 if function
+   "problem" gets inlined.
+   This example also shows the benefits of function
+   unswitching.  Without cloning, the loop will be done. */
+
+/* { dg-do run } */
+/* { dg-options "-O2 -fclone-hot-version-paths -fdump-tree-optimized" } */
+
+int __attribute__ ((version_selector))
+featureTest ()
+{
+  return 1;
+}
+
+int foo (int i)
+{
+  return i;
+}
+
+int bar (int i)
+{
+  return (11 - i);  
+}
+
+/* This calculates the sum of numbers from 1 to 10 in 2 different ways. */
+int __attribute__ ((hot))
+problem ()
+{
+  int ret = 0;
+  int j = 1;
+  for (j = 1; j<=10; j++)
+    ret += __builtin_dispatch (featureTest, (void *)foo, (void *)bar, j);
+  return ret;
+}
+
+int __attribute__ ((hot))
+main ()
+{
+  return problem() - 55;
+}
+
+
+/* { dg-final { scan-tree-dump "return 55" "optimized" } } */
+/* { dg-final { cleanup-tree-dump "optimized" } } */
Index: testsuite/gcc.dg/mversn4.c
===================================================================
--- testsuite/gcc.dg/mversn4.c	(revision 0)
+++ testsuite/gcc.dg/mversn4.c	(revision 0)
@@ -0,0 +1,29 @@
+/* Check that static feature test functions are correctly handled. This
+   test case also needs mversn4a.c.  extern_func calls foo and returns 0.*/
+   
+/* { dg-do run } */
+/* { dg-additional-sources "mversn4a.c" } */
+/* { dg-options "-O2" } */
+
+#include "mversn4.h"
+
+extern int extern_func ();
+
+int foo ()
+{
+  return 0;
+}
+
+int bar ()
+{
+  return 1;
+}
+
+int __attribute__ ((cold))
+main ()
+{
+  int a = 1, b = 1;
+  a  = extern_func ();
+  b  = __builtin_dispatch (featureTest, (void *)bar, (void *) foo);
+  return a * b;
+}
Index: testsuite/gcc.dg/mversn4.h
===================================================================
--- testsuite/gcc.dg/mversn4.h	(revision 0)
+++ testsuite/gcc.dg/mversn4.h	(revision 0)
@@ -0,0 +1,5 @@
+static int __attribute__ ((version_selector))
+featureTest ()
+{
+  return 1;
+}
Index: testsuite/gcc.dg/mversn4a.c
===================================================================
--- testsuite/gcc.dg/mversn4a.c	(revision 0)
+++ testsuite/gcc.dg/mversn4a.c	(revision 0)
@@ -0,0 +1,13 @@
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+
+#include "mversn4.h"
+
+extern int foo ();
+extern int bar ();
+
+
+int extern_func ()
+{
+  return __builtin_dispatch (featureTest, (void *)foo, (void *) bar);
+}
Index: testsuite/gcc.dg/torture/mversn1.c
===================================================================
--- testsuite/gcc.dg/torture/mversn1.c	(revision 0)
+++ testsuite/gcc.dg/torture/mversn1.c	(revision 0)
@@ -0,0 +1,31 @@
+/* Check that __builtin_dispatch gets converted and the executable runs fine. 
+   Since featureTest () returns 1, foo should be called and return 0.  Cloning
+   and Hoisting is not turned on here. */
+/* { dg-do run } */
+
+int __attribute__ ((version_selector))
+featureTest ()
+{
+  return 1;
+}
+
+int __attribute__ ((cold))
+foo ()
+{
+  return 0;
+}
+
+int __attribute__ ((cold))
+bar ()
+{
+  return 1;
+}
+
+int __attribute__ ((cold))
+main ()
+{
+  int a, b;
+  a = __builtin_dispatch (featureTest, (void *)foo, (void *) bar);
+  b = __builtin_dispatch (featureTest, (void *)bar, (void *) foo);
+  return a * b;
+}
Index: testsuite/gcc.dg/mversn2.c
===================================================================
--- testsuite/gcc.dg/mversn2.c	(revision 0)
+++ testsuite/gcc.dg/mversn2.c	(revision 0)
@@ -0,0 +1,47 @@
+/* This checks if cloning works correctly.  Since dispatch and fn1 are hot, they
+   should be cloned.  main should not be cloned.*/
+
+/* { dg-do run } */
+/* { dg-options "-O2 -fclone-hot-version-paths -fdump-tree-optimized" } */
+
+int __attribute__ ((version_selector))
+featureTest ()
+{
+  return 1;
+}
+
+int __attribute__ ((cold))
+foo ()
+{
+  return 0;
+}
+
+int __attribute__ ((cold))
+bar ()
+{
+  return 1;
+}
+
+int __attribute__ ((hot))
+dispatch ()
+{
+  return __builtin_dispatch (featureTest, (void *)foo, (void *) bar);
+}
+int __attribute__ ((hot))
+fn1 ()
+{
+  return dispatch ();
+}
+
+int __attribute__ ((cold))
+main ()
+{
+  return fn1 ();
+}
+
+/* { dg-final { scan-tree-dump "fn1_clone_1" "optimized" } } */
+/* { dg-final { scan-tree-dump "dispatch_clone_0" "optimized" } } */
+/* { dg-final { scan-tree-dump "dispatch_clone_1" "optimized" } } */
+/* { dg-final { scan-tree-dump-not "main_clone_0" "optimized" } } */
+/* { dg-final { scan-tree-dump-not "main_clone_1" "optimized" } } */
+/* { dg-final { cleanup-tree-dump "optimized" } } */
Index: testsuite/gcc.dg/mversn6.c
===================================================================
--- testsuite/gcc.dg/mversn6.c	(revision 0)
+++ testsuite/gcc.dg/mversn6.c	(revision 0)
@@ -0,0 +1,29 @@
+/* Check that __builtin_dispatch gets converted and the executable runs fine. 
+   when featureTest () is not marked with "version_selector". foo should be 
+   called and return 0.  Cloning and Hoisting is also done. */
+/* { dg-do run } */
+/* { dg-options "-O2 -fclone-hot-version-paths" } */
+
+int
+featureTest ()
+{
+  return 1;
+}
+
+int __attribute__ ((cold))
+foo ()
+{
+  return 0;
+}
+
+int __attribute__ ((cold))
+bar ()
+{
+  return 1;
+}
+
+int __attribute__ ((cold))
+main ()
+{
+  return __builtin_dispatch (featureTest, (void *)foo, (void *) bar);
+}
Index: testsuite/gcc.dg/mversn3.c
===================================================================
--- testsuite/gcc.dg/mversn3.c	(revision 0)
+++ testsuite/gcc.dg/mversn3.c	(revision 0)
@@ -0,0 +1,30 @@
+/* Simple check if parameters are passed correctly. */
+
+/* { dg-do run } */
+/* { dg-options "-O2 -fclone-hot-version-paths" } */
+
+int __attribute__ ((version_selector))
+featureTest ()
+{
+  return 1;
+}
+
+int __attribute__ ((cold))
+foo (int a)
+{
+  if (a == 1729)
+    return 0;
+  return 1;
+}
+
+int __attribute__ ((cold))
+bar (int a)
+{
+  return 1;
+}
+
+int __attribute__ ((cold))
+main ()
+{
+  return __builtin_dispatch (featureTest, (void *)foo, (void *) bar, 1729);
+}
Index: testsuite/g++.dg/mversn8.C
===================================================================
--- testsuite/g++.dg/mversn8.C	(revision 0)
+++ testsuite/g++.dg/mversn8.C	(revision 0)
@@ -0,0 +1,45 @@
+/* Call the caller of __builtin_dispatch indirectly.  Specify the
+   feature test function as a function pointer.  Make sure cloning
+   still happens. */
+
+/* { dg-do run } */
+/* { dg-options "-O2 -fclone-hot-version-paths -fdump-tree-optimized" } */
+
+int __attribute__ ((version_selector))
+featureTest ()
+{
+  return 1;
+}
+
+int
+foo ()
+{
+  return 0;
+}
+
+int
+bar ()
+{
+  return 1;
+}
+
+int __attribute__ ((hot))
+dispatch ()
+{
+  int (*funcp)() = featureTest;
+  int ret = __builtin_dispatch (funcp, (void *)foo, (void *)bar);
+  return ret;
+}
+
+int __attribute__ ((hot))
+main (int argc, char **argv)
+{
+  int (*ptr)() = dispatch;
+  return (*ptr)();
+}
+
+/* { dg-final { scan-tree-dump "dispatchv_clone_0" "optimized" } } */
+/* { dg-final { scan-tree-dump "dispatchv_clone_1" "optimized" } } */
+/* { dg-final { scan-tree-dump "main_clone_0" "optimized" } } */
+/* { dg-final { scan-tree-dump "main_clone_1" "optimized" } } */
+/* { dg-final { cleanup-tree-dump "optimized" } } */
Index: testsuite/g++.dg/mversn10a.C
===================================================================
--- testsuite/g++.dg/mversn10a.C	(revision 0)
+++ testsuite/g++.dg/mversn10a.C	(revision 0)
@@ -0,0 +1,37 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fclone-hot-version-paths -fdump-tree-optimized" } */
+
+static int __attribute__ ((version_selector))
+featureTest ()
+{
+  return 1;
+}
+
+static int foo ()
+{
+  return 0;
+}
+
+static int bar ()
+{
+  return 1;
+}
+
+static int __attribute__ ((noinline))
+dispatch ()
+{
+  __builtin_dispatch (featureTest, (void *)foo, (void *)bar);
+  return 0;
+}
+
+int
+fn2 ()
+{
+  for (int i = 0; i < 1000; i++)
+    dispatch ();
+  return 0;
+}
+
+/* { dg-final { scan-tree-dump "dispatchv_clone_0" "optimized" } } */
+/* { dg-final { scan-tree-dump "dispatchv_clone_1" "optimized" } } */
+/* { dg-final { cleanup-tree-dump "optimized" } } */
Index: testsuite/g++.dg/mversn14a.C
===================================================================
--- testsuite/g++.dg/mversn14a.C	(revision 0)
+++ testsuite/g++.dg/mversn14a.C	(revision 0)
@@ -0,0 +1,8 @@
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+
+int __attribute__ ((version_selector))
+featureTest ()
+{
+  return 1;
+}
Index: testsuite/g++.dg/tree-prof/mversn13.C
===================================================================
--- testsuite/g++.dg/tree-prof/mversn13.C	(revision 0)
+++ testsuite/g++.dg/tree-prof/mversn13.C	(revision 0)
@@ -0,0 +1,37 @@
+/* Make sure -fprofile-generate and -fprofile-use work fine. */
+
+/* { dg-options "-O2 -fclone-hot-version-paths" } */
+
+static int glob = 0;
+int __attribute__ ((version_selector))
+featureTest ()
+{
+  return glob;
+}
+
+int bar (int i)
+{
+  if (i > 500)
+    return 2 * i;
+  return 3 * i;
+}
+
+int foo (int i)
+{
+  bar (i);
+}
+
+int
+dispatch ()
+{
+  int ret = 0;
+  for (int i = 0; i < 1000; i++)
+    ret += __builtin_dispatch (featureTest, (void *)foo, (void *)bar,  i);
+  return ret;
+}
+
+int main ()
+{
+  int val = dispatch ();
+  return val > 10000000;
+}
Index: testsuite/g++.dg/tree-prof/mversn15.C
===================================================================
--- testsuite/g++.dg/tree-prof/mversn15.C	(revision 0)
+++ testsuite/g++.dg/tree-prof/mversn15.C	(revision 0)
@@ -0,0 +1,23 @@
+/* Make sure LIPO works correctly. dispatch is defined in mversn15a.C. It either
+   calls foo or bar and both returns 1. So, the value of ret is always 1000.
+   After cross-module inlining, main must return 0. */
+
+/* { dg-additional-sources "mversn15a.C" } */
+/* { dg-options "-O2 -fclone-hot-version-paths -fripa -fdump-tree-optimized" } */
+
+extern int foo ();
+extern int bar ();
+extern int dispatch ();
+
+int
+main ()
+{
+  int ret = 0;
+  for (int i = 1; i <= 1000; i++)
+   ret += dispatch ();
+  return ret - 1000;
+}
+
+/* { dg-final-use { scan-tree-dump "main_clone" "optimized" } } */
+/* { dg-final-use { scan-tree-dump "return 0" "optimized" } } */
+/* { dg-final-use { cleanup-tree-dump "optimized" } } */
Index: testsuite/g++.dg/tree-prof/mversn15a.C
===================================================================
--- testsuite/g++.dg/tree-prof/mversn15a.C	(revision 0)
+++ testsuite/g++.dg/tree-prof/mversn15a.C	(revision 0)
@@ -0,0 +1,26 @@
+/* { dg-options "-O2 -fclone-hot-version-paths -fripa" } */
+/* { dg-additional-sources "mversn15.C" } */
+
+#include <stdio.h>
+
+inline int
+ __attribute__ ((version_selector))
+featureTest()
+{
+  return 1;
+}
+
+int foo ()
+{
+  return 1;
+}
+
+int bar ()
+{
+  return 1;
+}
+
+int dispatch ()
+{
+  return __builtin_dispatch (featureTest, (void *)foo, (void *)bar);
+}
Index: testsuite/g++.dg/mversn9.C
===================================================================
--- testsuite/g++.dg/mversn9.C	(revision 0)
+++ testsuite/g++.dg/mversn9.C	(revision 0)
@@ -0,0 +1,30 @@
+/* Two __builtin_dispatch calls in different basic blocks. */
+
+/* { dg-do run } */
+/* { dg-options "-O2 -fclone-hot-version-paths" } */
+
+int __attribute__ ((version_selector))
+featureTest ()
+{
+  return 1;
+}
+
+int
+foo ()
+{
+  return 0;
+}
+
+int
+bar ()
+{
+  return 1;
+}
+
+int main (int argc, char **argv)
+{
+  if (argc)
+   return __builtin_dispatch (featureTest, (void *)foo, (void *)bar);
+  else
+   return (__builtin_dispatch (featureTest, (void *)bar, (void *)foo) - 1);
+}
Index: testsuite/g++.dg/mversn10.C
===================================================================
--- testsuite/g++.dg/mversn10.C	(revision 0)
+++ testsuite/g++.dg/mversn10.C	(revision 0)
@@ -0,0 +1,54 @@
+/* The purpose of this test is to check if the attributes of the clone
+   correctly shadow the parent function.  In this case, function "dispatch"
+   is cloned but is a static function.  The other file, "mversn10a.C" also
+   has a dispatch function that is cloned.  So, if the attributes of the
+   clone are not correct the linker will complain. */
+
+/* { dg-do run } */
+/* { dg-additional-sources "mversn10a.C" } */
+/* { dg-options "-O2 -fclone-hot-version-paths -fdump-tree-optimized" } */
+
+static int __attribute__ ((version_selector))
+featureTest ()
+{
+  return 1;
+}
+
+static int foo ()
+{
+  return 0;
+}
+
+static int bar ()
+{
+  return 1;
+}
+
+static int __attribute__ ((noinline))
+dispatch ()
+{
+  __builtin_dispatch (featureTest, (void *)foo, (void *)bar);
+  return 0;
+}
+
+int
+fn1 ()
+{
+  for (int i = 0; i < 1000; i++)
+    dispatch ();
+  return 0;
+}
+
+extern int fn2 ();
+
+int __attribute__ ((hot))
+main ()
+{
+  fn1 ();
+  fn2 ();
+  return 0;
+}
+
+/* { dg-final { scan-tree-dump "dispatchv_clone_0" "optimized" } } */
+/* { dg-final { scan-tree-dump "dispatchv_clone_1" "optimized" } } */
+/* { dg-final { cleanup-tree-dump "optimized" } } */
Index: testsuite/g++.dg/mversn12.C
===================================================================
--- testsuite/g++.dg/mversn12.C	(revision 0)
+++ testsuite/g++.dg/mversn12.C	(revision 0)
@@ -0,0 +1,43 @@
+/* Check if everything is fine if the versioned functions are static
+   member functions. */
+
+/* { dg-do run } */
+/* { dg-options "-O2 -fclone-hot-version-paths" } */
+
+int  __attribute__ ((version_selector))
+featureTest()
+{
+  return 1;;
+}
+
+class TestClass
+{
+ public:
+  static int foo ()
+  {
+    return 0;
+  }
+
+  static int bar ()
+  {
+    return 1;
+  }
+
+  int dispatch ()
+  {
+    int a = __builtin_dispatch (featureTest,
+                               (void*)(&TestClass::foo),
+			       (void*)(&TestClass::bar));
+    int b = __builtin_dispatch (featureTest,
+                               (void*)(&TestClass::bar),
+			       (void*)(&TestClass::foo));
+    return a * b;
+  }
+};
+
+int
+main ()
+{
+  TestClass c1;
+  return c1.dispatch ();
+}
Index: testsuite/g++.dg/mversn14.C
===================================================================
--- testsuite/g++.dg/mversn14.C	(revision 0)
+++ testsuite/g++.dg/mversn14.C	(revision 0)
@@ -0,0 +1,26 @@
+/* Check if everything is fine when the feature test body is in a different
+   module that does not have a __builtin-dispatch".  Requires mversn14a.C. */
+
+/* { dg-do run } */
+/* { dg-additional-sources "mversn14a.C" } */
+/* { dg-options "-O2 -fclone-hot-version-paths" } */
+
+int __attribute__ ((version_selector))
+featureTest ();
+
+int
+foo ()
+{
+  return 0;
+}
+
+int
+bar ()
+{
+  return 1;
+}
+
+int main ()
+{
+   return __builtin_dispatch (featureTest, (void *)foo, (void *)bar);
+}
Index: testsuite/g++.dg/mversn16.C
===================================================================
--- testsuite/g++.dg/mversn16.C	(revision 0)
+++ testsuite/g++.dg/mversn16.C	(revision 0)
@@ -0,0 +1,39 @@
+/* dispatch is cloned. Make sure the double is returned to main correctly. */
+
+/* { dg-do run } */
+/* { dg-options "-O2 -fclone-hot-version-paths -fdump-tree-optimized" } */
+
+#include "assert.h"
+
+int __attribute__ ((version_selector))
+featureTest ()
+{
+  return 1;
+}
+
+static int foo ()
+{
+  return 0;
+}
+
+static int bar ()
+{
+  return 1;
+}
+
+double
+dispatch ()
+{
+  __builtin_dispatch (featureTest, (void *)foo, (void *)bar);
+  return 2.536;
+}
+
+int main ()
+{
+  double d = dispatch ();
+  assert (d == 2.536);
+  return 0; 
+}
+
+/* { dg-final { scan-tree-dump "dispatchv_clone" "optimized" } } */
+/* { dg-final { cleanup-tree-dump "optimized" } } */
Index: testsuite/g++.dg/torture/mversn11.C
===================================================================
--- testsuite/g++.dg/torture/mversn11.C	(revision 0)
+++ testsuite/g++.dg/torture/mversn11.C	(revision 0)
@@ -0,0 +1,40 @@
+/* Check if parameters are passed correctly to the versioned function. */
+
+/* { dg-do run } */
+
+#include <stdio.h>
+#include <assert.h>
+
+int __attribute__ ((version_selector))
+featureTest ()
+{
+  return 1;
+}
+
+int __attribute__ ((noinline))
+foo (int n1, double n2, char n3)
+{
+  assert (n1 == 10);
+  assert (n2 == 20.0);
+  assert (n3 == 'c');
+  return n1;
+}
+
+
+int __attribute__ ((noinline))
+bar (int n1, double n2, char n3)
+{
+  assert (n1 == 10);
+  assert (n2 == 20.0);
+  assert (n3 == 'c');
+  return (n1 - 10);
+}
+
+int main ()
+{
+  int a = __builtin_dispatch (featureTest, (void *)foo, (void *)bar,
+                              10, 20.0, 'c');
+  int b = __builtin_dispatch (featureTest, (void *)bar, (void *)foo,
+                              10, 20.0, 'c');
+  return a * b;
+}
Index: testsuite/g++.dg/torture/mversn5.C
===================================================================
--- testsuite/g++.dg/torture/mversn5.C	(revision 0)
+++ testsuite/g++.dg/torture/mversn5.C	(revision 0)
@@ -0,0 +1,28 @@
+/* Check that global inline feature test functions are correctly handled. This
+   test case also needs mversn5a.c.  extern_func calls foo and returns 0.*/
+
+/* { dg-do run } */
+/* { dg-additional-sources "mversn5a.C" } */
+
+#include "mversn5.h"
+
+extern int extern_func ();
+
+int foo ()
+{
+  return 0;
+}
+
+int bar ()
+{
+  return 1;
+}
+
+int __attribute__ ((cold))
+main ()
+{
+  int a = 1, b = 1;
+  a  = extern_func ();
+  b  = __builtin_dispatch (featureTest, (void *)bar, (void *) foo);
+  return a * b;
+}
Index: testsuite/g++.dg/torture/mversn5.h
===================================================================
--- testsuite/g++.dg/torture/mversn5.h	(revision 0)
+++ testsuite/g++.dg/torture/mversn5.h	(revision 0)
@@ -0,0 +1,5 @@
+inline int __attribute__ ((version_selector))
+featureTest ()
+{
+  return 1;
+}
Index: testsuite/g++.dg/torture/mversn5a.C
===================================================================
--- testsuite/g++.dg/torture/mversn5a.C	(revision 0)
+++ testsuite/g++.dg/torture/mversn5a.C	(revision 0)
@@ -0,0 +1,12 @@
+/* { dg-do compile } */
+
+#include "mversn5.h"
+
+extern int foo ();
+extern int bar ();
+
+
+int extern_func ()
+{
+  return __builtin_dispatch (featureTest, (void *)foo, (void *) bar);
+}
Index: builtin-types.def
===================================================================
--- builtin-types.def	(revision 173122)
+++ builtin-types.def	(working copy)
@@ -475,3 +475,7 @@ DEF_FUNCTION_TYPE_VAR_5 (BT_FN_INT_INT_INT_INT_INT
 DEF_POINTER_TYPE (BT_PTR_FN_VOID_VAR, BT_FN_VOID_VAR)
 DEF_FUNCTION_TYPE_3 (BT_FN_PTR_PTR_FN_VOID_VAR_PTR_SIZE,
 		     BT_PTR, BT_PTR_FN_VOID_VAR, BT_PTR, BT_SIZE)
+
+DEF_POINTER_TYPE (BT_PTR_FN_INT, BT_FN_INT)
+DEF_FUNCTION_TYPE_VAR_3 (BT_FN_INT_PTR_FN_INT_PTR_PTR_VAR,
+			 BT_INT, BT_PTR_FN_INT, BT_PTR, BT_PTR)
Index: builtins.def
===================================================================
--- builtins.def	(revision 173122)
+++ builtins.def	(working copy)
@@ -760,6 +760,9 @@ DEF_BUILTIN (BUILT_IN_EMUTLS_REGISTER_COMMON,
 	     true, true, true, ATTR_NOTHROW_LEAF_LIST, false,
 	     !targetm.have_tls)
 
+/* Multiversioning builtin dispatch hook. */
+DEF_GCC_BUILTIN (BUILT_IN_DISPATCH, "dispatch", BT_FN_INT_PTR_FN_INT_PTR_PTR_VAR, ATTR_NULL)
+
 /* Exception support.  */
 DEF_BUILTIN_STUB (BUILT_IN_UNWIND_RESUME, "__builtin_unwind_resume")
 DEF_BUILTIN_STUB (BUILT_IN_CXA_END_CLEANUP, "__builtin_cxa_end_cleanup")
Index: mversn-dispatch.c
===================================================================
--- mversn-dispatch.c	(revision 0)
+++ mversn-dispatch.c	(revision 0)
@@ -0,0 +1,1760 @@
+/* Mulitversion Dispatch Pass.
+   Copyright (C) 2011 Free Software Foundation, Inc.
+   Contributed by Sriraman Tallam (tmsriram@google.com)
+
+This file is part of GCC.
+
+GCC is free software; you can redistribute it and/or modify it under
+the terms of the GNU General Public License as published by the Free
+Software Foundation; either version 3, or (at your option) any later
+version.
+
+GCC is distributed in the hope that it will be useful, but WITHOUT ANY
+WARRANTY; without even the implied warranty of MERCHANTABILITY or
+FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+for more details.
+
+You should have received a copy of the GNU General Public License
+along with GCC; see the file COPYING3.  If not see
+<http://www.gnu.org/licenses/>. */
+
+
+/* This pass processes __builtin_dispatch calls to call multi-versioned
+   functions. Only two versions are supported now. Example use :
+
+  int popcnt_sse4(unsigned int x) __attribute__((__target__("popcnt")));
+  int popcnt_sse4(unsigned int x)
+  {
+    int count = __builtin_popcount(x);
+    return count;
+  }
+
+  int popcnt(unsigned int x) __attribute__((__target__("no-popcnt")));
+  int popcnt(unsigned int x)
+  {
+    int count = __builtin_popcount(x);
+    return count;
+  }
+
+  int testsse() __attribute__((version_selector));
+  int main ()
+  {
+    ...
+    ret = __builtin_dispatch (testsse,  (void*)popcnt_sse4, (void*)popcnt, 25);
+    ...
+  }
+
+  There are two passes that are run to achieve multi-versioning.
+  "pass_ipa_multiversion_dispatch" is an ipa pass that decides which functions
+  have to be cloned and hoists the feature-test calls appropriately.  This
+  pass can be enabled with the flag "-fclone-hot-version-paths" and disabled
+  with "-fno-clone-hot-version-paths".
+
+  "pass_tree_convert_builtin_dispatch" does the lowering.  It is a
+  function-level pass.  Functions marked with attribute "version_selector" are
+  also handled by this pass.  This pass is always on.
+
+  How to use __builtin_dispatch ?
+  -----------------------------
+
+  __builtin_dispatch takes 3 mandatory arguments :
+
+  __builtin_dispatch (arg1, arg2, arg3, <arg4>, <arg5>, ...);
+
+  arg1 is the pointer to the feature-test function.
+  arg2 is the ( void *) cast pointer to the versioned function that is
+  executed when the feature test returns 1.
+  arg3 is the ( void *) cast pointer to the versioned function that is
+  executed when the feature test returns 0.
+  arg4, arg5, ... are optional. They are the arguments to the versioned
+  functions.  Both versions must accept the same number of arguments.
+  The __builtin_dispatch function returns the value returned by the
+  versioned function that gets executed.  The versioned function arg2
+  is executed when the feature_test function arg1 returns 1 and arg3
+  is executed when the feature_test function arg1 returns 0. arg1
+  could be marked as a "version_selector" function if it is a pure
+  function with no side-effects, returns a constant at run-time and
+  can be evaluated at any point in the execution.
+
+  When to use the "version_selector" attribute ?
+  -----------------------------------------------
+
+  Functions are marked with attribute "version_selector" only if
+  they are run-time constants.  Example of such functions would
+  be those that test if a specific feature is available on a
+  particular architecture.  Such functions must return a positive
+  integer. For two-way functions, those that test if a feature
+  is present or not must return 1 or 0 respectively.
+
+
+  The code is organized into five parts.  The first part has the functionality
+  to detect and handle functions marked with attribute "version_selector".  The
+  second part is the analysis phase where we find calls to __builtin_dispatch
+  and mark all functions that are hot and have a call-graph path to a
+  __builtin_dispatch call.  The third part decides which functions
+  to clone.  This is based on the number of clones that have to be created for
+  the functions marked in the analysis phase. Only two clones are allowed for
+  a function currently.  The fourth part is where the actual cloning happens.
+  The fifth part contains the implementation to lower the __builtin_dispatch
+  calls.
+
+  Flags : -fclone-hot-version-paths does function unswitching via cloning.
+          --param=num-mversn-clones=<num> allows to specify the number of
+          functions that should be cloned.
+	  --param=mversn-clone-depth=<num> allows to specify the length of
+          the call graph path that should be cloned.  num = 0 implies only
+          leaf node that contains the __builtin_dispatch statement must be
+          cloned. */
+
+#include "config.h"
+#include "system.h"
+#include "coretypes.h"
+#include "tm.h"
+#include "tree.h"
+#include "tree-inline.h"
+#include "langhooks.h"
+#include "flags.h"
+#include "cgraph.h"
+#include "diagnostic.h"
+#include "toplev.h"
+#include "timevar.h"
+#include "params.h"
+#include "fibheap.h"
+#include "intl.h"
+#include "tree-pass.h"
+#include "hashtab.h"
+#include "coverage.h"
+#include "ggc.h"
+#include "tree-flow.h"
+#include "rtl.h"
+#include "ipa-prop.h"
+#include "basic-block.h"
+#include "toplev.h"
+#include "dbgcnt.h"
+#include "tree-dump.h"
+#include "output.h"
+#include "vecprim.h"
+#include "gimple-pretty-print.h"
+
+typedef struct cgraph_node* NODEPTR;
+DEF_VEC_P (NODEPTR);
+DEF_VEC_ALLOC_P (NODEPTR, heap);
+
+/* Store the decl of __builtin_dispatch */
+static tree builtin_function_decl = NULL;
+
+/* Hash to map name to a decl.  Used for variables and functions. */
+static htab_t name_decl_htab = NULL;
+
+/* Hashtable helpers for name_decl_htab. */
+
+static hashval_t
+name_decl_htab_hash_descriptor (const void *p)
+{
+  const_tree t = (const_tree) p;
+  const char *name
+    = (IDENTIFIER_POINTER (DECL_NAME (t)));
+  return htab_hash_string(name);
+}
+
+/* Hashtable helper for name_decl_htab. */
+
+static int
+name_decl_htab_eq_descriptor (const void *p1, const void *p2)
+{
+  const_tree t1 = (const_tree) p1;
+  const char *c1 = IDENTIFIER_POINTER (DECL_NAME (t1));
+  const char *c2 = (const char *)p2;
+
+  return (strcmp (c1, c2) == 0);
+}
+
+/* Return true if NODE is a hot function.  It is a hot function
+   if its execution frequency is determined to be hot or
+   if any of its incoming or outgoing call-graph edges is hot.  */
+
+static bool
+hot_function_p (struct cgraph_node *node)
+{
+  struct cgraph_edge *edge;
+
+  if (node->frequency == NODE_FREQUENCY_HOT)
+    return true;
+
+  for (edge = node->callees; edge; edge = edge->next_callee)
+    if (cgraph_maybe_hot_edge_p (edge))
+      return true;
+
+  for (edge = node->callers; edge; edge = edge->next_caller)
+    if (cgraph_maybe_hot_edge_p (edge))
+      return true;
+
+  return false;
+}
+
+/* Return the number of arguments that a function has.  */
+
+static int
+function_args_count (tree fntype)
+{
+  function_args_iterator args_iter;
+  tree t;
+  int num = 0;
+
+  if (fntype)
+    {
+      FOREACH_FUNCTION_ARGS(fntype, t, args_iter)
+	{
+	  num++;
+	}
+    }
+
+  return num;
+}
+
+/* Return the variable name (global/constructor) to use for the
+   version_selector function with name of DECL by appending SUFFIX. */
+
+static char *
+make_name (tree decl, const char *suffix)
+{
+  char *global_var_name;
+  int name_len;
+  const char *name;
+
+  name = IDENTIFIER_POINTER (DECL_ASSEMBLER_NAME (decl));
+
+  name_len = strlen (name) + strlen (suffix) + 2;
+  global_var_name = (char *) xmalloc (name_len);
+  snprintf (global_var_name, name_len, "%s_%s", name, suffix);
+  return global_var_name;
+}
+
+/* Code for handling version_selector attribute functions.  Such functions are
+   run-time constants and need to be executed only once.  They are hoisted
+   to a static constructor and their result is stored in a global.
+ */
+
+
+/* This function returns the global variable / constructor name created
+   for feature-test functions marked with attribute "version_selector".
+   The name returned is the DECL name appended with
+   "version_selector_global" for the variable and
+   "version_selector_constructor" for the constructor. */
+
+static char*
+make_feature_test_global_name (tree decl, bool is_constructor)
+{
+  if (is_constructor)
+    return make_name (decl, "version_selector_constructor");
+
+  return make_name (decl, "version_selector_global");
+}
+
+/* This function creates a new VAR_DECL with attributes set
+   using the parameters.  PUBLIK corresponds to TREE_PUBLIC,
+   EXTERNAL corresponds to DECL_EXTERNAL and comdat is
+   for DECL_ONE_ONLY.  The global variable will have the
+   same status as the version_selector function.*/
+
+static tree
+allocate_new_var (const char *name, int publik,
+                  int external, int comdat)
+{
+  tree new_global_var;
+  struct varpool_node *vnode;
+
+  new_global_var = build_decl (UNKNOWN_LOCATION,
+			       VAR_DECL,
+	  	               get_identifier (name),
+		               integer_type_node);
+
+  DECL_EXTERNAL (new_global_var) = external;
+  TREE_STATIC (new_global_var) = 1;
+  TREE_PUBLIC (new_global_var) = publik;
+  DECL_INITIAL (new_global_var) = 0;
+  DECL_ARTIFICIAL (new_global_var) = 1;
+  DECL_PRESERVE_P (new_global_var) = 1;
+
+  if (comdat)
+    make_decl_one_only (new_global_var, DECL_ASSEMBLER_NAME (new_global_var));
+  assemble_variable (new_global_var, 0, 0, 0);
+
+  vnode = varpool_node (new_global_var);
+  gcc_assert (vnode != NULL);
+  /* Set finalized to 1, otherwise it asserts in function "write_symbol" in
+     lto-streamer-out.c. */
+  vnode->finalized = 1;
+  
+  return new_global_var;
+}
+
+/* Make a new constructor function here to call a feature-test function
+   and set its body to CONSTRUCTOR_BODY.  Its public and comdat
+   attributes are set from the parameters, PUBLIK, and COMDAT.
+   VERSION_SELECTOR_VAR is the global decl that saves the result of the
+   feature-test function in the constructor. */
+
+static tree
+make_constructor_function (char *name, gimple constructor_body, int publik,
+			   int comdat, tree version_selector_var)
+{
+  tree decl, type, t;
+  gimple_seq seq;
+  basic_block new_bb;
+  tree old_current_function_decl;
+
+  type = build_function_type_list (void_type_node, NULL_TREE);
+
+  if (dump_file)
+    fprintf (dump_file, "Name of new constructor function = %s\n", name);
+
+  decl = build_fn_decl (name, type);
+
+  DECL_NAME (decl) = get_identifier (name);
+  SET_DECL_ASSEMBLER_NAME (decl, DECL_NAME (decl));
+  gcc_assert (cgraph_node (decl) != NULL);
+
+  TREE_USED (decl) = 1;
+  DECL_ARTIFICIAL (decl) = 1;
+  DECL_IGNORED_P (decl) = 0;
+  TREE_PUBLIC (decl) = publik;
+  DECL_UNINLINABLE (decl) = 1;
+  DECL_EXTERNAL (decl) = 0;
+  DECL_CONTEXT (decl) = NULL_TREE;
+  DECL_INITIAL (decl) = make_node (BLOCK);
+  DECL_STATIC_CONSTRUCTOR (decl) = 1;
+  TREE_READONLY (decl) = 0;
+  DECL_PURE_P (decl) = 0;
+
+  if (comdat)
+    make_decl_one_only (decl, DECL_ASSEMBLER_NAME (decl));
+
+  /* Build result decl and add to function_decl. */
+  t = build_decl (UNKNOWN_LOCATION, RESULT_DECL, NULL_TREE, void_type_node);
+  DECL_ARTIFICIAL (t) = 1;
+  DECL_IGNORED_P (t) = 1;
+  DECL_RESULT (decl) = t;
+
+  gimplify_function_tree (decl);
+
+  /* Build CFG for this function. */
+
+  old_current_function_decl = current_function_decl;
+  push_cfun (DECL_STRUCT_FUNCTION (decl));
+  current_function_decl = decl;
+  init_empty_tree_cfg_for_function (DECL_STRUCT_FUNCTION (decl));
+  new_bb = create_empty_bb (ENTRY_BLOCK_PTR);
+  make_edge (ENTRY_BLOCK_PTR, new_bb, EDGE_FALLTHRU);
+
+  /* XXX: Not sure if the edge commented below is necessary.  If I add this
+     edge, it fails in gimple_verify_flow_info in tree-cfg.c in condition :
+     " if (e->flags & EDGE_FALLTHRU)"
+     during -fprofile-generate.
+     Otherwise, it is fine.  Deleting this edge does not break anything.
+     Commenting this so that it is clear I am intentionally not doing this.*/
+  /* make_edge (new_bb, EXIT_BLOCK_PTR, EDGE_FALLTHRU); */
+
+  seq = gimple_seq_alloc_with_stmt (constructor_body);
+
+  set_bb_seq (new_bb, seq);
+  gimple_set_bb (constructor_body, new_bb);
+
+  /* Set the lexical block of the constructor body. Fails the inliner
+     other wise. */
+  gimple_set_block (constructor_body, DECL_INITIAL (decl));
+
+  /* This call is very important if this pass runs when the IR is in
+     SSA form.  It breaks things in strange ways otherwise. */
+  init_tree_ssa (DECL_STRUCT_FUNCTION (decl));
+  add_referenced_var (version_selector_var);
+
+  cgraph_add_new_function (decl, true);
+  cgraph_call_function_insertion_hooks (cgraph_node (decl));
+  cgraph_mark_needed_node (cgraph_node (decl));
+
+  if (dump_file)
+    dump_function_to_file (decl, dump_file, TDF_BLOCKS);
+
+  pop_cfun ();
+  current_function_decl = old_current_function_decl;
+  return decl;
+}
+
+/* If  the current function is marked with attribute
+   "version_selector" then it is the predicate (feature-test) function
+   for multi-versioning.  Call this function in a constructor and assign
+   the return value to a global variable.
+   The constructor's name is the decl name suffixed
+   "version_selector_constructor" and the global variable's name is the
+   decl name suffixed with "version_selector_global"
+
+   For example, feature-test function isSSE4 marked with attribute
+   version_selector is converted to
+
+   void isSSE4_version_selector_constructor ()
+   {
+     isSSE4_version_selector_global = isSSE4 ();
+   }
+
+   This function returns the decl of the global variable.
+
+   THIS_DECL is the function decl of the "version_selector" function.
+   */
+
+static tree
+handle_version_selector_attr_function (tree this_decl)
+{
+  char *global_var_name;
+  tree version_selector_var = NULL;
+  void **slot;
+
+  gcc_assert (!flag_lto);
+
+  if (dump_file)
+    fprintf (dump_file, "Creating constructor/global for function %s\n",
+	     IDENTIFIER_POINTER (DECL_NAME (this_decl)));
+
+  global_var_name = make_feature_test_global_name (this_decl,
+                                                   false);
+
+  slot = htab_find_slot_with_hash (name_decl_htab, global_var_name,
+                                   htab_hash_string (global_var_name),
+                                   INSERT);
+  if (*slot == NULL)
+    {
+      if (dump_file)
+        fprintf (dump_file, "Creating global variable %s\n",
+	         global_var_name);
+      *slot = allocate_new_var (global_var_name,
+                                TREE_PUBLIC (this_decl),
+                                DECL_EXTERNAL (this_decl),
+                                DECL_ONE_ONLY (this_decl));
+    }
+  else
+    {
+      free (global_var_name);
+      return (tree) *slot;
+    }
+
+  version_selector_var = (tree) *slot;
+
+  /* If the feature-test function is not external, create a constructor and
+     call this function in the constructor. */
+
+  if (!DECL_EXTERNAL (this_decl))
+    {
+      char *constructor_name;
+      gimple constructor_body;
+      tree constructor_decl;
+
+      constructor_name
+        = make_feature_test_global_name (this_decl, true);
+
+      constructor_body = gimple_build_call (this_decl, 0);
+
+      gimple_call_set_lhs (constructor_body, version_selector_var);
+
+      if (dump_file)
+        print_gimple_stmt (dump_file, constructor_body, 0, TDF_VOPS);
+
+      constructor_decl =
+        make_constructor_function (constructor_name, constructor_body,
+				   TREE_PUBLIC (this_decl),
+				   DECL_ONE_ONLY (this_decl),
+			           version_selector_var);
+
+      gcc_assert (constructor_decl != NULL_TREE);
+      free (constructor_name);
+    }
+
+  free (global_var_name);
+  return version_selector_var;
+}
+
+/* Start Analysis phase.  Mark all functions that are hot and have a call-graph
+   path to a __builtin_dispatch call. */
+
+/* This function returns the address of the feature test function.
+   If the address of the function is saved to a temporary,
+   this function traverses the gimple statements before BUILTIN_STMT
+   and finds an assignment whose rhs is the feature test function.
+   If the feature test function is specified as a function pointer
+   whose function value is unknown, this funcition returns NULL. */
+
+static tree
+find_version_selector_func_addr (gimple builtin_stmt)
+{
+  tree cond_func_addr = NULL;
+  gimple def_stmt = NULL;
+
+  cond_func_addr = gimple_call_arg (builtin_stmt, 0);
+
+  gcc_assert (TREE_CODE (cond_func_addr) == ADDR_EXPR
+	      || TREE_CODE (cond_func_addr) == SSA_NAME);
+
+  if (TREE_CODE (cond_func_addr) == ADDR_EXPR)
+    return cond_func_addr;
+
+  /* TREE_CODE (cond_func_addr) ==  SSA_NAME
+     This means a new function pointer variable is created and assigned the
+     address of the feature-test function. Traverse the statements backwards
+     and find the assignment to get the RHS. */
+
+  def_stmt = SSA_NAME_DEF_STMT (cond_func_addr);
+
+  gcc_assert (def_stmt
+              && gimple_assign_lhs (def_stmt) == cond_func_addr);
+
+  cond_func_addr = gimple_assign_rhs1 (def_stmt);
+
+  /* If the cond_func_addr is still not an ADDR_EXPR, it means that the
+     feature-test function is specified as a pointer.  In this case, we
+     return NULL, since the feature-test function decl is not known. */
+
+  if (cond_func_addr == NULL
+      || TREE_CODE (cond_func_addr) != ADDR_EXPR)
+    return NULL;
+
+  /* If the operand of the ADDR_EXPR is not a function_decl, return NULL
+     as this still means the feature-test function is specified as a
+     function pointer. */
+
+  if (TREE_CODE (TREE_OPERAND (cond_func_addr, 0)) != FUNCTION_DECL)
+    return NULL;
+
+  return cond_func_addr;
+}
+
+/* Finds the gimple calls  to __builtin_dispatch in function pointed
+   to by the call graph NODE and populates the vector VEC.  Returns
+   true if at least one statement was found where the feature test
+   function is marked as "version_selector".  Otherwise, there is no
+   question of hoisting it. */
+
+static bool
+is_builtin_dispatch_stmt_present (struct cgraph_node *node,
+			          VEC (tree,heap) **vec)
+{
+  struct cgraph_edge *edge;
+  bool present = false;
+
+  gcc_assert (!flag_lto);
+
+  for (edge = node->callees; edge; edge = edge->next_callee)
+    {
+      if (edge->callee->decl == builtin_function_decl)
+        {
+	  tree cond_func_decl;
+	  tree cond_func_addr;
+	  gcc_assert (*vec != NULL);
+	  cond_func_addr = find_version_selector_func_addr (edge->call_stmt);
+
+	  if (cond_func_addr == NULL)
+            continue;
+
+	  cond_func_decl = TREE_OPERAND (cond_func_addr, 0);
+
+	  /* Do not consider for hoisting if "version_selector" attribute is
+	     not set. */
+	  if (lookup_attribute ("version_selector",
+			        DECL_ATTRIBUTES (cond_func_decl)) == NULL)
+            {
+              if (dump_file)
+                {
+                  fprintf (dump_file, "Not hoisting builtin_dispatch as "
+                           "feature_test function not version_selector :\n");
+                  print_gimple_stmt (dump_file, edge->call_stmt, 0, TDF_VOPS);
+		}
+              continue;
+            }
+
+	  present = true;
+	  VEC_safe_push (tree, heap, *vec, cond_func_decl);
+        }
+    }
+  return present;
+}
+
+/* Updates the list of feature-test function decls reaching the cgraph
+   function NODE. */
+
+static void
+update_reachable_decls_list (struct cgraph_node *node,
+                             VEC (tree, heap) *predicate_decls)
+{
+  VEC (tree, heap) **decl_list = NULL;
+  tree cond_func_decl;
+  int ix;
+
+  if (node->aux == NULL)
+    {
+      decl_list = (VEC (tree, heap) **) xmalloc (sizeof (VEC (tree, heap) *));
+      *decl_list = VEC_alloc (tree, heap, 1);
+      node->aux = decl_list;
+    }
+  else
+    decl_list = (VEC (tree, heap) **) node->aux;
+
+  for (ix = 0; VEC_iterate (tree, predicate_decls, ix, cond_func_decl); ++ix)
+    VEC_safe_push (tree, heap, *decl_list, cond_func_decl);
+}
+
+/* Propagate the __builtin_dispatch stmt (s) called from node to its
+   callers, PREDICATE_DECLS is the decls list of the predicate functions. */
+
+static unsigned int
+mark_reachable_functions (struct cgraph_node *this_node,
+			  VEC (tree, heap) *predicate_decls)
+{
+  VEC (NODEPTR, heap) *work_list;
+  VEC (int, heap) *depth_list;
+  struct cgraph_edge *e;
+  htab_t node_htab = NULL;
+  void **slot = NULL;
+
+  /* Use a work-list style algorithm to mark functions in any call-graph
+     path to the current function. */
+
+  work_list = VEC_alloc (NODEPTR, heap, 8);
+  depth_list = VEC_alloc (int, heap, 8);
+
+  VEC_safe_push (NODEPTR, heap, work_list, this_node);
+  VEC_safe_push (int, heap, depth_list, 0);
+
+  node_htab = htab_create (10, htab_hash_pointer,
+  			   htab_eq_pointer, NULL);
+
+  slot = htab_find_slot (node_htab, this_node, INSERT);
+
+  gcc_assert (*slot == NULL);
+  *slot = this_node;
+
+  while (!VEC_empty (NODEPTR, work_list))
+    {
+      struct cgraph_node *node = VEC_pop (NODEPTR, work_list);
+      int depth = VEC_pop (int, depth_list);
+
+      if (dump_file)
+        fprintf (dump_file, "%s has a depth = %d callgraph path to %s\n",
+                 cgraph_node_name (node), depth,
+                 cgraph_node_name (this_node));
+
+      update_reachable_decls_list (node, predicate_decls);
+
+      gcc_assert (node->aux != NULL);
+
+      if (depth >= PARAM_VALUE (PARAM_MVERSN_CLONE_CGRAPH_DEPTH))
+        {
+          if (dump_file)
+            fprintf (dump_file, "Not propogating __builtin_dispatch... "
+                     "maximum cloning depth  = %d reached\n",
+		     PARAM_VALUE (PARAM_MVERSN_CLONE_CGRAPH_DEPTH));
+          continue;
+        }
+
+      for (e = node->callers; e; e = e->next_caller)
+        {
+          slot = htab_find_slot (node_htab, e->caller, INSERT);
+	  if (*slot != NULL)
+	    continue;
+          *slot = e->caller;
+          if (!hot_function_p (e->caller))
+            continue;
+
+          VEC_safe_push (NODEPTR, heap, work_list, e->caller);
+          VEC_safe_push (int, heap, depth_list, (depth + 1));
+        }
+    }
+
+  htab_delete (node_htab);
+  VEC_free (NODEPTR, heap, work_list);
+  VEC_free (int, heap, depth_list);
+  return 0;
+}
+
+/* Scan the call graph and detect hot functions that have __builtin_dispatch
+   calls. Then, propogate this information to its callers. Returns true if
+   a suitable __builtin_dispatch was found. */
+
+static bool
+perform_analysis_phase (void)
+{
+  struct cgraph_node *node;
+  VEC(tree, heap) *builtin_predicates_vec = NULL;
+  bool flag = false;
+
+  builtin_predicates_vec = VEC_alloc (tree, heap, 1);
+
+  for (node = cgraph_nodes; node; node = node->next)
+    {
+      /* if the body of this decl is from outside, do nothing. */
+      if (DECL_EXTERNAL (node->decl))
+        continue;
+
+      if (!hot_function_p (node))
+        continue;
+
+      if (!is_builtin_dispatch_stmt_present (node, &builtin_predicates_vec))
+        continue;
+
+      if (dump_file)
+        {
+          fprintf (dump_file, "%s calls __builtin_dispatch atleast once.\n",
+                   cgraph_node_name (node));
+
+          fprintf (dump_file, "%s is a hot function, consider cloning ...\n",
+        	   cgraph_node_name (node));
+        }
+
+      flag = true;
+      mark_reachable_functions (node, builtin_predicates_vec);
+      VEC_truncate (tree, builtin_predicates_vec, 0);
+    }
+
+  VEC_free (tree, heap, builtin_predicates_vec);
+  return flag;
+}
+
+/* End Analysis phase. */
+
+/* Decide Cloning Phase.
+
+   In this phase, we go through each function and decide if it should be
+   cloned or not. */
+
+/* This function counts the number of unique decls in the DECL_LIST.*/
+
+static int
+count_predicate_functions (VEC (tree,heap) *decl_list)
+{
+  int ix;
+  int count = 0;
+  tree cond_func_decl = NULL;
+  htab_t dup_decl_htab = NULL;
+
+  if (VEC_length (tree, decl_list) == 1)
+    return 1;
+
+  dup_decl_htab = htab_create (2, htab_hash_pointer, htab_eq_pointer, NULL);
+
+  for (ix = 0; VEC_iterate (tree, decl_list, ix, cond_func_decl); ++ix)
+    {
+      void **slot = NULL;
+      slot = htab_find_slot (dup_decl_htab, cond_func_decl, INSERT);
+
+      if (*slot != NULL)
+        continue;
+      count++;
+      *slot = cond_func_decl;
+    }
+
+  htab_delete (dup_decl_htab);
+  return count;
+}
+
+/* This function decides which functions to clone based on the number of
+   feature_test decls reaching it.  Currently, only one feature_test decl
+   is allowed. */
+
+static bool
+decide_cloning_phase (void)
+{
+  struct cgraph_node *node;
+  int count;
+  bool run_cloning_phase = false;
+  int num_funcs_cloned = 0;
+
+  for (node = cgraph_nodes; node; node = node->next)
+    {
+      tree cond_func_decl = NULL;
+      VEC (tree, heap) *vec;
+      if (node->aux == NULL)
+        continue;
+
+      if (num_funcs_cloned >= PARAM_VALUE (PARAM_NUMBER_OF_MVERSN_CLONES))
+        {
+          if (dump_file)
+            fprintf (dump_file, "Reached cloning limit specified "
+                     "by \"num-mversn-clones\" for %s\n",
+	             cgraph_node_name (node));
+
+          free (node->aux);
+	  node->aux = NULL;
+	  continue;
+        }
+
+      vec = *(VEC (tree,heap) **) node->aux;
+      count = count_predicate_functions (vec);
+      gcc_assert (count >= 1);
+      cond_func_decl = VEC_index (tree, vec, 0);
+      gcc_assert (cond_func_decl != NULL);
+      VEC_free (tree, heap, vec);
+      free (node->aux);
+      node->aux = NULL;
+
+      if (count > 1)
+        {
+          if (dump_file)
+            fprintf (dump_file, "%s has %d predicates, Not cloning for > 1\n",
+	             cgraph_node_name (node), count);
+	  continue;
+        }
+      /* Set the node's aux value to be that of the predicate decl. */
+      node->aux = cond_func_decl;
+      run_cloning_phase = true;
+      num_funcs_cloned++;
+    }
+  return run_cloning_phase;
+}
+
+/* End Decide Cloning Phase. */
+
+/* Cloning Phase. */
+
+/* Deletes all basic-blocks and leaves function with :
+   ENTRY_BLOCK ---> (new empty basic block) ---> EXIT_BLOCK
+*/
+
+static basic_block
+empty_function_body (tree fndecl)
+{
+  basic_block bb, new_bb;
+  edge e;
+  tree old_current_function_decl;
+
+  old_current_function_decl = current_function_decl;
+  push_cfun (DECL_STRUCT_FUNCTION (fndecl));
+  current_function_decl = fndecl;
+
+  clear_edges ();
+  for (bb = ENTRY_BLOCK_PTR; bb != NULL;)
+    {
+      basic_block bb_next;
+      bb_next = bb->next_bb;
+      if (bb != EXIT_BLOCK_PTR
+          && bb != ENTRY_BLOCK_PTR)
+        {
+          if (bb_seq (bb) != NULL)
+            {
+              gimple_stmt_iterator i;
+              for (i = gsi_start_bb (bb); !gsi_end_p (i);)
+	        {
+		  gimple stmt = gsi_stmt (i);
+		  unlink_stmt_vdef (stmt);
+                  gsi_remove (&i, true);
+		  release_defs (stmt);
+		}
+            }
+          bb->il.gimple = NULL;
+          bb->prev_bb = NULL;
+          bb->next_bb = NULL;
+          SET_BASIC_BLOCK (bb->index, NULL);
+          n_basic_blocks--;
+        }
+      bb = bb_next;
+    }
+  ENTRY_BLOCK_PTR->next_bb = EXIT_BLOCK_PTR;
+  new_bb = create_empty_bb (ENTRY_BLOCK_PTR);
+  e = make_edge (ENTRY_BLOCK_PTR, new_bb, EDGE_FALLTHRU);
+  gcc_assert (e != NULL);
+  /* XXX:Is this edge necessary ? */
+  e = make_edge (new_bb, EXIT_BLOCK_PTR, EDGE_FALLTHRU);
+  gcc_assert (e != NULL);
+
+  current_function_decl = old_current_function_decl;
+  pop_cfun ();
+  return new_bb;
+}
+
+/* Takes function with decl ORIG_FNDECL and clones it.  The
+   name of the clone is the original name suffixed with
+   NAME_SUFFIX.  Code is adapted from cgraph_function_versioning
+   in cgraphunit.c */
+
+static tree
+clone_function (tree orig_fndecl, const char *name_suffix)
+{
+  tree new_decl;
+  char *new_name;
+  struct cgraph_node *new_version;
+  struct cgraph_node *old_version;
+  void **slot;
+  tree old_current_function_decl;
+
+  new_name = make_name (orig_fndecl, name_suffix);
+  new_decl = copy_node (orig_fndecl);
+
+
+  slot = htab_find_slot_with_hash (name_decl_htab, new_name,
+                                   htab_hash_string (new_name), INSERT);
+
+  gcc_assert (*slot == NULL);
+  *slot = new_decl;
+
+  /* Code adapted from cgraph_function_versioning in cgraphuinit.c */
+
+  new_version = cgraph_node (new_decl);
+  old_version = cgraph_node (orig_fndecl);
+
+  new_version->local = old_version->local;
+  new_version->global = old_version->global;
+  new_version->rtl = old_version->rtl;
+  new_version->reachable = true;
+  new_version->count = old_version->count;
+
+  /* Set the name of the new function. */
+  DECL_NAME (new_decl) = get_identifier (new_name);
+  SET_DECL_ASSEMBLER_NAME (new_decl, DECL_NAME (new_decl));
+  SET_DECL_RTL (new_decl, NULL);
+
+  tree_function_versioning (orig_fndecl, new_decl, NULL /*tree_map*/,
+                            false, NULL /*args_to_skip*/,
+			    NULL /* blocks_to_copy */ ,
+                            NULL /* new_entry */);
+
+
+  old_current_function_decl = current_function_decl;
+  push_cfun (DECL_STRUCT_FUNCTION (new_decl));
+  current_function_decl = new_decl;
+
+  TREE_READONLY (new_decl) = TREE_READONLY (orig_fndecl);
+  TREE_STATIC (new_decl) = TREE_STATIC (orig_fndecl);
+  TREE_USED (new_decl) = TREE_USED (orig_fndecl);
+  DECL_ARTIFICIAL (new_decl) = 1;
+  DECL_IGNORED_P (new_decl) = 0;
+  TREE_PUBLIC (new_decl) = TREE_PUBLIC (orig_fndecl);
+  DECL_CONTEXT (new_decl) = DECL_CONTEXT (orig_fndecl);
+
+  DECL_EXTERNAL (new_decl) = DECL_EXTERNAL (orig_fndecl);
+  DECL_COMDAT (new_decl) = DECL_COMDAT (orig_fndecl);
+  DECL_COMDAT_GROUP (new_decl) = DECL_COMDAT_GROUP (orig_fndecl);
+  DECL_VIRTUAL_P (new_decl) = DECL_VIRTUAL_P (orig_fndecl);
+  DECL_WEAK (new_decl) = DECL_WEAK (orig_fndecl);
+
+  /* Always inline the clones. Why are we cloning otherwise? */
+  DECL_DECLARED_INLINE_P (new_decl) = 1;
+  DECL_UNINLINABLE (new_decl) = 0;
+  new_version->local.externally_visible
+  = old_version->local.externally_visible;
+  new_version->local.local
+  = old_version->local.local;
+
+  new_version->analyzed = true;
+  new_version->lowered = true;
+
+  if (dump_file)
+    dump_function_to_file (new_decl, dump_file, TDF_BLOCKS);
+
+  cgraph_add_new_function (new_decl, true);
+
+  cgraph_call_function_insertion_hooks (new_version);
+  cgraph_mark_needed_node (new_version);
+
+  pop_cfun ();
+  current_function_decl = old_current_function_decl;
+
+  return new_decl;
+}
+
+/* This function populates the vector *VEC with the args in the gimple
+   call statement STMT. SKIP_ARGS is the number of args to skip.*/
+
+static void
+get_function_args (gimple stmt, int num_args, VEC (tree, heap) **vec,
+                   int skip_args)
+{
+  int i;
+
+  if (num_args == 0) return;
+
+  *vec = VEC_alloc (tree, heap, num_args);
+  /* The number of args in a function is 1 plus the actual number of
+     args.  Also, there are 3 special args reserved, so the first arg
+     starts from 3. */
+  for (i = 0; i <= num_args - 2; ++i)
+    VEC_quick_push (tree, *vec, gimple_call_arg (stmt, (skip_args + i)));
+}
+
+/* Given ret = __builtin_dispatch (pred, fn1, fn2, arg1, ....)
+   get ret = fn1 (arg1, ...) or ret = fn2 (arg1, ....)
+   depending on the value of SIDE == 0 or 1. */
+
+static gimple
+make_specialized_call_from_builtin (gimple builtin_stmt, int side)
+{
+  tree func_addr;
+  int num_func_args = 0;
+  VEC (tree, heap) *nargs = NULL;
+  tree lhs_stmt;
+  gimple specialized_call_stmt;
+
+  if (side == 0)
+    func_addr = gimple_call_arg (builtin_stmt, 1);
+  else
+    func_addr = gimple_call_arg (builtin_stmt, 2);
+
+  num_func_args
+    =  function_args_count (TREE_TYPE (TREE_OPERAND (func_addr, 0)));
+
+  get_function_args (builtin_stmt, num_func_args, &nargs, 3);
+
+  specialized_call_stmt = gimple_build_call_vec (func_addr, nargs);
+
+  lhs_stmt = gimple_call_lhs (builtin_stmt);
+
+  if (lhs_stmt != NULL_TREE)
+    gimple_call_set_lhs (specialized_call_stmt, lhs_stmt);
+
+  if (nargs != NULL)
+    VEC_free (tree, heap, nargs);
+
+  return specialized_call_stmt;
+}
+
+/* Given a call (GENERIC_STMT) to a function that is cloned, substitute
+   with a call to the correct clone. */
+
+static gimple
+make_specialized_call_to_clone (gimple generic_stmt, int side)
+{
+  tree new_decl;
+  char *new_name;
+  tree generic_fndecl;
+  gimple specialized_call_stmt;
+  void **slot;
+  int num_func_args;
+  tree lhs_stmt;
+  VEC (tree, heap) *nargs= NULL;
+
+  generic_fndecl = gimple_call_fndecl (generic_stmt);
+  gcc_assert (generic_fndecl != NULL);
+
+  if (side == 0)
+    new_name = make_name (generic_fndecl, "clone_0");
+  else
+    new_name = make_name (generic_fndecl, "clone_1");
+
+  slot = htab_find_slot_with_hash (name_decl_htab, new_name,
+                                   htab_hash_string (new_name), NO_INSERT);
+  gcc_assert (slot != NULL);
+  new_decl = (tree) *slot;
+  gcc_assert (new_decl);
+
+  num_func_args = function_args_count (TREE_TYPE (generic_fndecl));
+  get_function_args (generic_stmt, num_func_args, &nargs, 0);
+  specialized_call_stmt = gimple_build_call_vec (new_decl, nargs);
+
+  lhs_stmt = gimple_call_lhs (generic_stmt);
+
+  if (lhs_stmt != NULL_TREE)
+    gimple_call_set_lhs (specialized_call_stmt, lhs_stmt);
+
+  if (nargs != NULL)
+    VEC_free (tree, heap, nargs);
+
+  return specialized_call_stmt;
+}
+
+/* Returns true if STMT is a call to __builtin_dispatch and its
+   predicate feature-test function is marked with attribute
+   "version_selector". */
+
+static bool
+is_builtin_with_predicate_version_selector (gimple stmt)
+{
+  tree cond_func_addr, cond_func_decl;
+
+  gcc_assert (!flag_lto);
+ 
+  if (gimple_call_fndecl (stmt) != builtin_function_decl)
+    return false;
+
+  cond_func_addr = find_version_selector_func_addr (stmt);
+
+  if (cond_func_addr == NULL)
+    return false;
+
+  cond_func_decl = TREE_OPERAND (cond_func_addr, 0);
+  if (lookup_attribute ("version_selector",
+			DECL_ATTRIBUTES (cond_func_decl)) != NULL)
+    return true;
+
+  return false;
+}
+
+/* Find calls to __builtin_dispatch or to functions that are versioned
+   in CLONE_DECL and substitute the call with the correct version based
+   on the value of SIDE. */
+
+static void
+specialize_call (tree clone_decl, int side)
+{
+  basic_block bb;
+  tree old_current_function_decl;
+
+  old_current_function_decl = current_function_decl;
+  push_cfun (DECL_STRUCT_FUNCTION (clone_decl));
+  current_function_decl = clone_decl;
+
+  /* Iterate over call edges and find out if there is
+     a call to __builtin_dispatch or a cloned function.
+     We cannot iterate over call graph edges as there are
+     no edges for the clones yet. */
+
+  FOR_EACH_BB_FN (bb, DECL_STRUCT_FUNCTION (clone_decl))
+    {
+      gimple_stmt_iterator gsi;
+      for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi))
+        {
+	  tree callee_decl;
+	  struct cgraph_node *callee_node;
+	  gimple specialized_call_stmt;
+	  gimple stmt = gsi_stmt (gsi);
+
+	  if (!is_gimple_call (stmt))
+            continue;
+
+	  callee_decl = gimple_call_fndecl (stmt);
+
+	  if (callee_decl == NULL)
+            continue;
+
+	  callee_node = cgraph_node (callee_decl);
+
+	  /* For a __builtin_dispatch stmt, only specialize if
+             version_selector attribute is set. Otherwise, it is
+             not hoisted, so no specialization. */
+
+	  if (is_builtin_with_predicate_version_selector (stmt))
+	    {
+	      specialized_call_stmt =
+	        make_specialized_call_from_builtin (stmt, side);
+	    }
+	  else if  (callee_node->aux != NULL)
+            {
+	      specialized_call_stmt =
+	        make_specialized_call_to_clone (stmt, side);
+            }
+	  else
+	    continue;
+
+          if (dump_file)
+            {
+	      fprintf (dump_file, "Specialize stmt : \n");
+              print_gimple_stmt (dump_file, stmt, 0, TDF_VOPS);
+	      fprintf (dump_file, "Specialized stmt : \n");
+              print_gimple_stmt (dump_file, specialized_call_stmt,
+			         0, TDF_VOPS);
+            }
+
+	  gimple_set_block (specialized_call_stmt, gimple_block (stmt));
+	  gsi_insert_before_without_update (&gsi, specialized_call_stmt,
+                                            GSI_SAME_STMT);
+
+	  
+          unlink_stmt_vdef (stmt);
+	  gsi_remove (&gsi, true); 
+	  mark_symbols_for_renaming (specialized_call_stmt);
+
+	  /* After removing make sure gsi is set correctly to not skip
+	     a statememt. */
+          gsi = gsi_for_stmt (specialized_call_stmt);
+	}
+    }
+  current_function_decl = old_current_function_decl;
+  pop_cfun ();
+}
+
+/* When a function is version cloned, its body is replaced to call one
+   of the versions with the feature-test function acting as a predicate.
+   This is done with __builtin_dispatch which is later expanded. */
+
+static gimple
+make_builtin_call_to_clones (tree orig_fndecl, tree clone_0_addr,
+                             tree clone_1_addr, tree cond_func_addr)
+{
+  gimple new_builtin_call;
+  VEC(tree, heap) *vargs = VEC_alloc (tree, heap, 4);
+  tree arg;
+
+  VEC_quick_push (tree, vargs, cond_func_addr);
+  VEC_quick_push (tree, vargs, clone_0_addr);
+  VEC_quick_push (tree, vargs, clone_1_addr);
+
+  for (arg = DECL_ARGUMENTS (orig_fndecl); arg; arg = TREE_CHAIN (arg))
+    {
+      VEC_safe_push (tree, heap, vargs, arg);
+      /* Again, this add_referenced_var is very very important.  It broke
+         a build where a cloned function's arguments where never
+         referenced.  Missing this statement in places asserts at
+         tree-dfa.c:589, in function referenced_var_lookup at
+         "gcc_assert (h || uid == 0);" and is very difficult to triage. */
+      add_referenced_var (arg);
+    }
+
+  new_builtin_call = gimple_build_call_vec (builtin_function_decl, vargs);
+  mark_symbols_for_renaming (new_builtin_call);
+
+
+  if (dump_file)
+    print_gimple_stmt (dump_file, new_builtin_call, 0, TDF_VOPS);
+
+  VEC_free (tree, heap, vargs);
+
+  return new_builtin_call;
+}
+
+/* This clones a dispatch function whose callee-graph path has a function
+   which calls __builtin_dispatch.  This function is cloned and the
+   original function branches to the right clone. */
+
+static int
+clone_and_dispatch_function (struct cgraph_node *orig_node, tree *clone_0,
+			     tree *clone_1)
+{
+  tree clone_0_decl, clone_1_decl;
+  gimple new_builtin_call = NULL;
+  gimple new_return_stmt = NULL;
+  gimple_seq seq = NULL;
+  basic_block new_bb;
+  tree orig_fndecl;
+  tree return_var = NULL;
+  tree return_type;
+  tree old_current_function_decl;
+
+  old_current_function_decl = current_function_decl;
+  orig_fndecl = orig_node->decl;
+  push_cfun (DECL_STRUCT_FUNCTION (orig_fndecl));
+  current_function_decl = orig_fndecl;
+
+  /* Make 2 clones for true and false function. */
+  clone_0_decl = clone_function (orig_fndecl, "clone_0");
+  clone_1_decl = clone_function (orig_fndecl, "clone_1");
+  *clone_0 = clone_0_decl;
+  *clone_1 = clone_1_decl;
+
+  new_bb = empty_function_body (orig_fndecl);
+
+  new_builtin_call = make_builtin_call_to_clones (
+		       orig_fndecl,
+                       build_fold_addr_expr (clone_0_decl),
+		       build_fold_addr_expr (clone_1_decl),
+		       build_fold_addr_expr ((tree)orig_node->aux));
+
+  return_type = TREE_TYPE (TREE_TYPE (orig_fndecl));
+
+  if (!TREE_ADDRESSABLE (return_type) && COMPLETE_TYPE_P (return_type))
+    {
+      tree tmp_var;
+      tmp_var = create_tmp_var (return_type, NULL);
+      add_referenced_var (tmp_var);
+      return_var = make_ssa_name (tmp_var, new_builtin_call);
+      gimple_call_set_lhs (new_builtin_call, return_var);
+    }
+
+  mark_symbols_for_renaming (new_builtin_call);
+  new_return_stmt = gimple_build_return (return_var);
+  mark_symbols_for_renaming (new_return_stmt);
+  gimple_seq_add_stmt (&seq, new_builtin_call);
+  gimple_seq_add_stmt (&seq, new_return_stmt);
+  set_bb_seq (new_bb, seq);
+  gimple_set_bb (new_builtin_call, new_bb);
+  gimple_set_bb (new_return_stmt, new_bb);
+
+  gimple_set_block (new_builtin_call, DECL_INITIAL (orig_fndecl));
+  gimple_set_block (new_return_stmt, DECL_INITIAL (orig_fndecl));
+
+  if (dump_file)
+    dump_function_to_file (orig_fndecl, dump_file, TDF_BLOCKS);
+
+  /* This update_ssa is necessary here for the following reason.  SSA uses
+     a global syms_to_rename bitmap that stores syms that must be renamed.
+     So, if we accumulate the syms from one function in IPA but move to
+     a different function without updating SSA, then we could be
+     accumulating syms from many functions.  This would assert in
+     referenced_var_lookup because the hashtab storing the syms is
+     function local. This is horrible. gcc-4.6 makes this bitmap a
+     global. */
+  update_ssa (TODO_update_ssa);
+
+  compute_inline_parameters (cgraph_node (orig_fndecl));
+  DECL_DECLARED_INLINE_P (orig_fndecl) = 1;
+  DECL_UNINLINABLE (orig_fndecl) = 0;
+  current_function_decl = old_current_function_decl;
+  pop_cfun ();
+  return 0;
+}
+
+/* Clone all functions marked for cloning by the earlier phase. */
+
+static void
+perform_cloning_phase (void)
+{
+  struct cgraph_node *node;
+  int ix;
+  VEC (tree, heap) *cloned_decl_list = NULL;
+  tree cloned_decl = NULL;
+
+  cloned_decl_list = VEC_alloc (tree, heap, 2);
+
+  /* First clone, then specialize the clones. */
+  for (node = cgraph_nodes; node; node = node->next)
+    {
+      tree clone_0_decl, clone_1_decl;
+      if (node->aux == NULL)
+        continue;
+      if (dump_file)
+      {
+        fprintf (dump_file, "%s will be cloned\n", cgraph_node_name (node));
+        dump_function_to_file (node->decl, dump_file, TDF_BLOCKS);
+      }
+      clone_and_dispatch_function (node, &clone_0_decl, &clone_1_decl);
+      VEC_safe_push (tree, heap, cloned_decl_list, clone_0_decl);
+      VEC_safe_push (tree, heap, cloned_decl_list, clone_1_decl);
+      continue;
+    }
+
+  /* Specialize the clones now. */
+  for (ix = 0; VEC_iterate (tree, cloned_decl_list, ix, cloned_decl); ++ix)
+    {
+      int which_clone = ix % 2;
+      specialize_call (cloned_decl, which_clone);
+    }
+
+  VEC_free (tree, heap, cloned_decl_list);
+}
+
+/* End Cloning phase. */
+
+/* Checks if there is atleast one call to __builtin_dispatch. */
+
+static bool
+find_builtin_decl (void)
+{
+  struct cgraph_node *node;
+  for (node = cgraph_nodes; node; node = node->next)
+    {
+      if (strstr (cgraph_node_name (node), "__builtin_dispatch") != NULL)
+        {
+          builtin_function_decl = node->decl;
+          return true;
+        }
+    }
+  return false;
+}
+
+/* Set the aux fields of all nodes and edges in the call graph to be NULL. */
+
+static void
+cleanup_aux_field (void)
+{
+  struct cgraph_node *node;
+  struct cgraph_edge *edge;
+
+  for (node = cgraph_nodes; node; node = node->next)
+    {
+      node->aux = NULL;
+      for (edge = node->callees; edge; edge = edge->next_callee)
+        edge->aux = NULL;
+    }
+}
+
+/* Main driver function. It scans the __builtin_dispatch calls and
+   figures out which functions to clone.  It then clones the functions. */
+
+static unsigned int
+builtin_dispatch_ipa_clone (void)
+{
+  cleanup_aux_field ();
+
+  /* Allocate hashtab mapping name to decl. */
+  name_decl_htab = htab_create (10, name_decl_htab_hash_descriptor,
+			        name_decl_htab_eq_descriptor, NULL);
+
+  /* Turn it on for O1 and above.  At -O0, there is a SSA alias bug
+     with create_tmp_var.  Cloning and hoisting is not necessary at
+     -O0 anyways.  Also, guard it with the flag
+     "-fclone-hot-version-paths". 
+     Disabled for LTO as it needs more work. */
+  if (optimize == 0
+      || profile_arc_flag
+      || !flag_clone_hot_version_paths
+      || flag_lto)
+    return 0;
+
+  if (!find_builtin_decl ())
+    return 0;
+
+  gcc_assert (builtin_function_decl != NULL);
+
+  if (!perform_analysis_phase ())
+    {
+      cleanup_aux_field ();
+      return 0;
+    }
+
+  if (decide_cloning_phase ())
+    perform_cloning_phase ();
+
+  cleanup_aux_field ();
+
+  return 0;
+}
+
+static bool
+gate_handle_builtin_dispatch (void)
+{
+  return true;
+}
+
+struct simple_ipa_opt_pass pass_ipa_multiversion_dispatch =
+{
+ {
+  SIMPLE_IPA_PASS,
+  "multiversion_dispatch",		/* name */
+  gate_handle_builtin_dispatch,		/* gate */
+  builtin_dispatch_ipa_clone,           /* execute */
+  NULL,					/* sub */
+  NULL,					/* next */
+  0,					/* static_pass_number */
+  TV_MVERSN_DISPATCH,			/* tv_id */
+  0,	                                /* properties_required */
+  PROP_cfg,				/* properties_provided */
+  0,					/* properties_destroyed */
+  0,					/* todo_flags_start */
+  TODO_dump_func |			/* todo_flags_finish */
+  TODO_update_ssa
+ }
+};
+
+/* Lowering of the __builtin_dispatch calls. */
+
+
+/* This function converts STMT which is a __builtin_dispatch
+   call of the form :
+   ret = __builtin_dispatch (predicate, foo, bar, arg1, ...)
+   into :
+   var_1 = predicate
+   if  (var_1)
+     var_2 = foo (arg1, ...);
+   else
+     var_3 = bar (arg1, ...);
+   var_4 = phi (var_2, var_3)
+   ret = var_4
+
+   var_? are ssa names for variable var.
+*/
+
+static unsigned int
+convert_builtin_dispatch (gimple stmt)
+{
+  tree cond_func_addr, if_func_addr, else_func_addr;
+  tree cond_func_decl = NULL;
+  gimple if_part, else_part, if_else_stmt;
+  basic_block bb1, bb2, bb3, bb4;
+  gimple bb1end, bb2end, bb3end;
+  edge e12, e13, e23, e24, e34;
+  VEC(tree, heap) *nargs = NULL;
+  int num_func_args = 0, i;
+  tree version_selector_var;
+  tree lhs_result;
+  gimple_stmt_iterator gsi;
+  basic_block bb;
+  gimple feature_test_call = NULL;
+  tree tmp_var = NULL;
+  gimple init_stmt = NULL;
+  tree ssa_if_name, ssa_else_name;
+  gimple phinode = NULL;
+  tree tmp_result_var, ssa_result_var;
+
+  gsi = gsi_for_stmt (stmt);
+  bb = gsi_bb (gsi);
+
+  cond_func_addr = find_version_selector_func_addr (stmt);
+  if (cond_func_addr != NULL)
+    {
+      cond_func_decl = TREE_OPERAND (cond_func_addr, 0);
+      gcc_assert (cond_func_decl);
+    }
+
+  if (dump_file)
+    {
+      fprintf (dump_file, "Before Converting __builtin_dispatch :\n");
+      dump_function_to_file (current_function_decl, dump_file, TDF_BLOCKS);
+    }
+
+  if_func_addr = gimple_call_arg (stmt, 1);
+  else_func_addr = gimple_call_arg (stmt, 2);
+
+  tmp_result_var = create_tmp_var (integer_type_node, NULL);
+  add_referenced_var (tmp_result_var);
+
+  if (flag_lto
+      || cond_func_decl == NULL
+      || lookup_attribute ("version_selector",
+                           DECL_ATTRIBUTES (cond_func_decl)) == NULL)
+    {
+      tree arg = gimple_call_arg (stmt, 0);
+      /* This means the feature-test function is not set with attribute
+         version_selector or it is a function pointer or in LTO. So,
+         explicitly call it. */
+      feature_test_call = gimple_build_call (arg, 0);
+      ssa_result_var = make_ssa_name (tmp_result_var, feature_test_call);
+      gimple_assign_set_lhs (feature_test_call, ssa_result_var);
+      mark_symbols_for_renaming (feature_test_call);
+      version_selector_var = ssa_result_var;
+    }
+  else
+    {
+      /* Get the global corresponding to the "version_selector" function. */
+      version_selector_var
+        = handle_version_selector_attr_function (cond_func_decl);
+      gcc_assert (version_selector_var);
+      add_referenced_var (version_selector_var);
+      feature_test_call = gimple_build_assign (tmp_result_var,
+                                               version_selector_var);
+      ssa_result_var = make_ssa_name (tmp_result_var, feature_test_call);
+      gimple_assign_set_lhs (feature_test_call, ssa_result_var);
+      mark_symbols_for_renaming (feature_test_call);
+      version_selector_var = ssa_result_var;
+    }
+
+  if_else_stmt = gimple_build_cond (GT_EXPR,
+                                    version_selector_var,
+                                    integer_zero_node,
+                                    NULL_TREE, NULL_TREE);
+
+  mark_symbols_for_renaming (if_else_stmt);
+
+  num_func_args =  function_args_count (
+    TREE_TYPE (TREE_OPERAND (if_func_addr, 0)));
+
+  nargs = VEC_alloc (tree, heap, num_func_args);
+
+  /* The arguments to the feature test function start from the 4th argument
+     in __builtin_dispatch.  The first 3 arguments are mandatory. */
+
+  for (i = 0; i <= num_func_args - 2; ++i)
+    VEC_quick_push (tree, nargs,
+                    gimple_call_arg (stmt, (3 + i)));
+
+  if_part = gimple_build_call_vec (if_func_addr, nargs);
+  else_part = gimple_build_call_vec (else_func_addr, nargs);
+
+  lhs_result = gimple_call_lhs (stmt);
+
+  if (lhs_result != NULL_TREE)
+    {
+      tree ssa_var;
+      tree return_type;
+      return_type = TREE_TYPE (lhs_result);
+      tmp_var = create_tmp_var (return_type, NULL);
+      add_referenced_var (tmp_var);
+
+      init_stmt = gimple_build_assign (tmp_var, integer_zero_node);
+      ssa_var = make_ssa_name (tmp_var, init_stmt);
+      gimple_assign_set_lhs (init_stmt, ssa_var);
+      mark_symbols_for_renaming (init_stmt);
+
+      ssa_if_name = make_ssa_name (tmp_var, init_stmt);
+      ssa_else_name = make_ssa_name (tmp_var, init_stmt);
+      gimple_call_set_lhs (if_part, ssa_if_name);
+      gimple_call_set_lhs (else_part, ssa_else_name);
+    }
+  mark_symbols_for_renaming (if_part);
+  mark_symbols_for_renaming (else_part);
+
+  /* Set the lexical block to be the same as the dispatch call. */
+  gcc_assert (feature_test_call);
+  gimple_set_block (feature_test_call, gimple_block (stmt));
+
+  if (init_stmt)
+    gimple_set_block (init_stmt, gimple_block (stmt));
+
+  gimple_set_block (if_else_stmt, gimple_block (stmt));
+  gimple_set_block (if_part, gimple_block (stmt));
+  gimple_set_block (else_part, gimple_block (stmt));
+
+  gsi_insert_before_without_update (&gsi, feature_test_call, GSI_SAME_STMT);
+  gimple_set_bb (feature_test_call, bb);
+
+  if (init_stmt)
+    {
+      gsi_insert_before_without_update (&gsi, init_stmt,
+                                        GSI_SAME_STMT);
+      gimple_set_bb (init_stmt, bb);
+    }
+
+  gsi_insert_before_without_update (&gsi, if_else_stmt, GSI_SAME_STMT);
+  gsi_insert_before_without_update (&gsi, if_part, GSI_SAME_STMT);
+  gsi_insert_before_without_update (&gsi, else_part, GSI_SAME_STMT);
+
+  /* Remove the builtin_dispatch call after the expansion. */
+  unlink_stmt_vdef (stmt);
+  gsi_remove (&gsi, true);
+
+  bb1end = if_else_stmt;
+  bb2end = if_part;
+  bb3end = else_part;
+  bb1 = bb;
+  e12 = split_block (bb1, bb1end);
+  bb2 = e12->dest;
+  e23 = split_block (bb2, bb2end);
+  bb3 = e23->dest;
+  e34 = split_block (bb3, bb3end);
+  bb4 = e34->dest;
+
+  e12->flags &= ~EDGE_FALLTHRU;
+  e12->flags |= EDGE_TRUE_VALUE;
+  e13 = make_edge (bb1, bb3, EDGE_FALSE_VALUE);
+  gcc_assert (e13);
+  e24 = make_edge (bb2, bb4, EDGE_FALLTHRU);
+  gcc_assert (e24);
+  remove_edge (e23);
+
+  if (tmp_var)
+    {
+      gimple assign_stmt;
+      phinode = create_phi_node (tmp_var, bb4);
+      add_phi_arg (phinode, ssa_if_name, e24, UNKNOWN_LOCATION);
+      add_phi_arg (phinode, ssa_else_name, e34, UNKNOWN_LOCATION);
+      mark_symbols_for_renaming (phinode);
+      gcc_assert (lhs_result);
+      assign_stmt
+        = gimple_build_assign (lhs_result, gimple_phi_result (phinode));
+      mark_symbols_for_renaming (assign_stmt);
+      gsi = gsi_start_bb (bb4);
+      gsi_insert_before_without_update (&gsi, assign_stmt, GSI_SAME_STMT);
+      gimple_set_bb (assign_stmt, bb4);
+    }
+
+  if (dump_file)
+    {
+      fprintf (dump_file, "Converted __builtin_dispatch :\n");
+      dump_function_to_file (current_function_decl, dump_file, TDF_BLOCKS);
+    }
+
+  return 0;
+}
+
+/* This function does two things.
+
+   1) For a feature-test function marked with attribute "version_selector",
+      it creates a constructor that calls the feature-test function and a
+      global that holds the result.  The global's result will be used
+      to lower any __builtin_dispatch statement that refers to this feature
+      test function.  The __builtin_dispatch statement and the feature test
+      function can be in different modules.
+
+   2) It lowers __builtin_dispatch statements. */
+
+static unsigned int
+do_convert_builtin_dispatch (void)
+{
+  basic_block bb;
+  gimple_stmt_iterator gsi;
+  VEC (gimple, heap) *builtin_stmt_list = NULL;
+  int ix;
+  gimple builtin_stmt;
+
+  /* Allocate hashtab mapping name to decl. */
+  if (name_decl_htab == NULL)
+    name_decl_htab = htab_create (10, name_decl_htab_hash_descriptor,
+		                  name_decl_htab_eq_descriptor, NULL);
+
+  /* Look for functions with attribute "version_selector" and make a
+     constructor which calls the function and saves the result in a
+     global.  Disabled for LTO as it needs more work. */
+
+  if (!flag_lto
+      && lookup_attribute ("version_selector",
+                           DECL_ATTRIBUTES (current_function_decl)) != NULL)
+    {
+      if (dump_file)
+        fprintf (dump_file, "Function with version_selector attribute found :"
+                 " %s.  Making constructor for it.\n",
+		 current_function_name ());
+
+      handle_version_selector_attr_function (current_function_decl);
+      /* Assume there are no __builtin_dispatch calls in feature test
+	 functions.  So it is safe to return. */
+      return 0;
+    }
+
+  /* Find and lower __builtin_dispatch calls. */
+
+  FOR_EACH_BB_FN (bb, DECL_STRUCT_FUNCTION (current_function_decl))
+    {
+      for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi))
+        {
+          gimple stmt = gsi_stmt (gsi);
+          tree call_decl;
+
+          if (!is_gimple_call (stmt))
+            continue;
+
+          call_decl = gimple_call_fndecl (stmt);
+
+	  if (call_decl == NULL)
+            continue;
+
+          if (strstr (cgraph_node_name (cgraph_node (call_decl)),
+                      "__builtin_dispatch") == NULL)
+            continue;
+
+	  if (dump_file)
+            {
+	      fprintf (dump_file, "Converting __builtin_dispatch stmt in:%s\n",
+		       current_function_name ());
+              print_gimple_stmt (dump_file, stmt, 0, TDF_VOPS);
+            }
+
+	  if (builtin_stmt_list == NULL)
+              builtin_stmt_list = VEC_alloc (gimple, heap, 2);
+
+          gcc_assert (builtin_stmt_list != NULL);
+	  VEC_safe_push (gimple, heap, builtin_stmt_list, stmt);
+        }
+    }
+
+  if (!builtin_stmt_list)
+    return 0;
+ 
+  for (ix = 0; VEC_iterate (gimple, builtin_stmt_list, ix, builtin_stmt);
+       ++ix)
+    convert_builtin_dispatch (builtin_stmt);
+
+  compute_inline_parameters (cgraph_node (current_function_decl));
+ 
+  VEC_free (gimple, heap, builtin_stmt_list); 
+  
+  return 0;
+}
+
+static bool
+gate_convert_builtin_dispatch (void)
+{
+  return true;
+}
+
+struct gimple_opt_pass pass_tree_convert_builtin_dispatch =
+{
+ {
+  GIMPLE_PASS,
+  "convert_builtin_dispatch",	        /* name */
+  gate_convert_builtin_dispatch,	/* gate */
+  do_convert_builtin_dispatch,		/* execute */
+  NULL,					/* sub */
+  NULL,					/* next */
+  0,					/* static_pass_number */
+  TV_MVERSN_DISPATCH,			/* tv_id */
+  PROP_cfg,				/* properties_required */
+  PROP_cfg,				/* properties_provided */
+  0,					/* properties_destroyed */
+  0,					/* todo_flags_start */
+  TODO_verify_stmts | TODO_dump_func |	/* todo_flags_finish */
+  TODO_cleanup_cfg | TODO_dump_cgraph |
+  TODO_update_ssa | TODO_verify_ssa
+ }
+};
Index: timevar.def
===================================================================
--- timevar.def	(revision 173122)
+++ timevar.def	(working copy)
@@ -106,6 +106,7 @@ DEFTIMEVAR (TV_LEX		     , "lexical analysis")
 DEFTIMEVAR (TV_PARSE                 , "parser")
 DEFTIMEVAR (TV_NAME_LOOKUP           , "name lookup")
 DEFTIMEVAR (TV_INLINE_HEURISTICS     , "inline heuristics")
+DEFTIMEVAR (TV_MVERSN_DISPATCH       , "multiversion dispatch")
 DEFTIMEVAR (TV_INTEGRATION           , "integration")
 DEFTIMEVAR (TV_TREE_GIMPLIFY	     , "tree gimplify")
 DEFTIMEVAR (TV_TREE_EH		     , "tree eh")
Index: common.opt
===================================================================
--- common.opt	(revision 173122)
+++ common.opt	(working copy)
@@ -2191,6 +2191,10 @@ ftree-builtin-call-dce
 Common Report Var(flag_tree_builtin_call_dce) Init(0) Optimization
 Enable conditional dead code elimination for builtin calls
 
+fclone-hot-version-paths
+Common Report Var(flag_clone_hot_version_paths) Init(0)
+Enable cloning and hoisting of hot multiversioned paths
+
 fwhole-program
 Common Report Var(flag_whole_program) Init(0) Optimization
 Perform whole program optimizations
Index: Makefile.in
===================================================================
--- Makefile.in	(revision 173122)
+++ Makefile.in	(working copy)
@@ -1304,6 +1304,7 @@ OBJS-common = \
 	mcf.o \
 	mode-switching.o \
 	modulo-sched.o \
+	mversn-dispatch.o \
 	omega.o \
 	omp-low.o \
 	optabs.o \
@@ -3097,6 +3098,11 @@ implicit-zee.o : implicit-zee.c $(CONFIG_H) $(SYST
    $(DF_H) $(TIMEVAR_H) tree-pass.h $(RECOG_H) $(EXPR_H) \
    $(REGS_H) $(TREE_H) $(TM_P_H) insn-config.h $(INSN_ATTR_H) $(DIAGNOSTIC_CORE_H) \
    $(TARGET_H) $(OPTABS_H) insn-codes.h rtlhooks-def.h $(PARAMS_H) $(CGRAPH_H)
+mversn-dispatch.o : mversn-dispatch.c $(CONFIG_H) $(SYSTEM_H) coretypes.h $(TM_H) \
+   $(TREE_H) langhooks.h $(TREE_INLINE_H) $(FLAGS_H) $(CGRAPH_H) intl.h \
+   $(DIAGNOSTIC_H) $(FIBHEAP_H) $(PARAMS_H) $(TIMEVAR_H) tree-pass.h \
+   $(HASHTAB_H) $(COVERAGE_H) $(GGC_H) $(TREE_FLOW_H) $(RTL_H) $(IPA_PROP_H) \
+   $(BASIC_BLOCK_H) $(TOPLEV_H) $(TREE_DUMP_H)
 gcse.o : gcse.c $(CONFIG_H) $(SYSTEM_H) coretypes.h $(TM_H) $(RTL_H) \
    $(REGS_H) hard-reg-set.h $(FLAGS_H) insn-config.h $(GGC_H) \
    $(RECOG_H) $(EXPR_H) $(BASIC_BLOCK_H) $(FUNCTION_H) output.h toplev.h $(DIAGNOSTIC_CORE_H) \
Index: passes.c
===================================================================
--- passes.c	(revision 173122)
+++ passes.c	(working copy)
@@ -796,6 +796,15 @@ init_optimization_passes (void)
     }
   NEXT_PASS (pass_ipa_increase_alignment);
   NEXT_PASS (pass_ipa_matrix_reorg);
+  NEXT_PASS (pass_ipa_multiversion_dispatch);
+    {
+      struct opt_pass **p = &pass_ipa_multiversion_dispatch.pass.sub;
+      NEXT_PASS (pass_tree_convert_builtin_dispatch);
+      /* Rebuilding cgraph edges is necessary as the above passes change
+         the call graph.  Otherwise, future optimizations use the old
+	 call graph and make wrong decisions sometimes.*/
+      NEXT_PASS (pass_rebuild_cgraph_edges);
+    }
   NEXT_PASS (pass_ipa_lower_emutls);
   *p = NULL;
 
Index: params.def
===================================================================
--- params.def	(revision 173122)
+++ params.def	(working copy)
@@ -929,6 +929,17 @@ DEFPARAM (CXX_MAX_NAMESPACES_FOR_DIAGNOSTIC_HELP,
 	  "name lookup fails",
 	  1000, 0, 0)
 
+DEFPARAM (PARAM_NUMBER_OF_MVERSN_CLONES,
+          "num-mversn-clones",
+	  "maximum number of functions to be cloned while doing "
+          "multiversioning",
+	  10, 0, 1000)
+
+DEFPARAM (PARAM_MVERSN_CLONE_CGRAPH_DEPTH,
+          "mversn-clone-depth",
+	  "maximum length of the call graph path to be cloned "
+          "while doing multiversioning",
+	  2, 0, 5)
 /*
 Local variables:
 mode:c
