Patchwork loop-unroll.c TLC 2/4

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Submitter Jan Hubicka
Date Oct. 20, 2012, 3:53 p.m.
Message ID <20121020155323.GA4688@kam.mff.cuni.cz>
Download mbox | patch
Permalink /patch/192924/
State New
Headers show

Comments

Jan Hubicka - Oct. 20, 2012, 3:53 p.m.
Hi,
this patch fixes heuristic on decide_unroll_constant_iterations to take into
account the profile: even when the loop is known to have constant loop
iteration bound, it doesn't need to really iterate many times.  So use profile
and loop_max to double check that this is the case.

Bootstrapped/regtested x86_64-linux, comitted.

Honza

	* loop-unroll.c (decide_unroll_constant_iterations): Don't
	perform unrolling for loops with low iterations bounds or estimates.

Patch

Index: loop-unroll.c
===================================================================
--- loop-unroll.c	(revision 192632)
+++ loop-unroll.c	(working copy)
@@ -519,6 +519,7 @@  decide_unroll_constant_iterations (struc
 {
   unsigned nunroll, nunroll_by_av, best_copies, best_unroll = 0, n_copies, i;
   struct niter_desc *desc;
+  double_int iterations;
 
   if (!(flags & UAP_UNROLL))
     {
@@ -561,8 +562,14 @@  decide_unroll_constant_iterations (struc
       return;
     }
 
-  /* Check whether the loop rolls enough to consider.  */
-  if (desc->niter < 2 * nunroll)
+  /* Check whether the loop rolls enough to consider.  
+     Consult also loop bounds and profile; in the case the loop has more
+     than one exit it may well loop less than determined maximal number
+     of iterations.  */
+  if (desc->niter < 2 * nunroll
+      || ((estimated_loop_iterations (loop, &iterations)
+	   || max_loop_iterations (loop, &iterations))
+	  && iterations.ult (double_int::from_shwi (2 * nunroll))))
     {
       if (dump_file)
 	fprintf (dump_file, ";; Not unrolling loop, doesn't roll\n");
Index: testsuite/gcc.dg/tree-prof/unroll-1.c
===================================================================
--- testsuite/gcc.dg/tree-prof/unroll-1.c	(revision 0)
+++ testsuite/gcc.dg/tree-prof/unroll-1.c	(revision 0)
@@ -0,0 +1,24 @@ 
+/* { dg-options "-O3 -fdump-rtl-loop2_unroll -funroll-loops -fno-peel-loops" } */
+void abort ();
+
+int a[1000];
+int
+__attribute__ ((noinline))
+t()
+{
+  int i;
+  for (i=0;i<1000;i++)
+    if (!a[i])
+      return 1;
+  abort ();
+}
+main()
+{
+  int i;
+  for (i=0;i<1000;i++)
+    t();
+  return 0;
+}
+/* { dg-final-use { scan-rtl-dump "Considering unrolling loop with constant number of iterations" "loop2_unroll" } } */
+/* { dg-final-use { cleanup-rtl-dump "Not unrolling loop, doesn't roll" } } */
+/* { dg-options "-O3 -fdump-rtl-loop2_unroll -funroll-loops -fno-peel-loops" } */