Patchwork Reload/i386 patch for secondary memory vs subregs

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Submitter Bernd Schmidt
Date Aug. 3, 2012, 2:33 p.m.
Message ID <501BE12F.2000205@codesourcery.com>
Download mbox | patch
Permalink /patch/175003/
State New
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Comments

Bernd Schmidt - Aug. 3, 2012, 2:33 p.m.
There are a number of problems in the interaction between secondary
memory and subregs. If we reload the inner of a subreg, we forget about
this when deciding whether to use secondary memory, and just use
REGNO_REG_CLASS on the (now reloaded) inner.

Also, we don't really know what to do if we get a subreg of something
that's not a register, such as a symbol_ref. This is another part of the
patch below, using a variant of find_valid_class that works in this case.

The original testcase we had was the artificial test included in the
patch, which involves reinterpreting a pointer to a string constant as a
floating point value. Since then, we've also found a larger Altivec
testcase which crashes the compiler without this patch.

Bootstrapped and tested on i686-linux. It's also been in several of our
internal trees, going back to even 4.4-based ones IIRC, and has had
testing for several architectures. Ok for the i386 part? I intend to
check the reload bits in soon if there are no objections.


Bernd
John David Anglin - Aug. 11, 2012, 2:20 p.m.
> 	* reload1.c (replaced_subreg): New static function.
> 	(gen_reload): Use it when deciding whether to use secondary
> 	memory.

This causes the following on hppa*-*-* (32-bit):

../../gcc/gcc/reload1.c: In function 'rtx_def* gen_reload(rtx, rtx, int, reload_
type)':
../../gcc/gcc/reload1.c:8494:12: error: unused variable 'tem1' [-Werror=unused-v
ariable]
   rtx tem, tem1, tem2;
	       ^
	       ../../gcc/gcc/reload1.c:8494:18: error: unused variable 'tem2' [-Werror=unused-variable]
		  rtx tem, tem1, tem2;
				    ^
				    ../../gcc/gcc/reload1.c: At global scope:
				    ../../gcc/gcc/reload1.c:8477:1: error: 'rtx_def* replaced_subreg(rtx)' defined but not used [-Werror=unused-function]
				     replaced_subreg (rtx x)
				      ^
				      cc1plus: all warnings being treated as errors
				      make[3]: *** [reload1.o] Error 1

Dave

Patch

	* reload.c (find_valid_class_1): New static function.
	(push_reload): Use it when reloading a SYMBOL_REG as the inner
	of a subreg.  Keep better track of needed classes for the
	secondary memory case.
	* config/i386/i386.h (LIMIT_RELOAD_CLASS): Limit INT_SSE_REGS to
	GENERAL_REGS.
	* reload1.c (replaced_subreg): New static function.
	(gen_reload): Use it when deciding whether to use secondary
	memory.

Index: gcc/reload.c
===================================================================
--- gcc/reload.c	(revision 189284)
+++ gcc/reload.c	(working copy)
@@ -707,6 +707,55 @@  find_valid_class (enum machine_mode oute
 
   return best_class;
 }
+
+/* We are trying to reload a subreg of something that is not a register.
+   Find the largest class which has at least one register valid in
+   mode MODE.  OUTER is the mode of the subreg, DEST_CLASS the class in
+   which we would eventually like to obtain the object.  */
+
+static enum reg_class
+find_valid_class_1 (enum machine_mode outer ATTRIBUTE_UNUSED,
+		    enum machine_mode mode ATTRIBUTE_UNUSED,
+		    enum reg_class dest_class ATTRIBUTE_UNUSED)
+{
+  int best_cost = -1;
+  int rclass;
+  int regno;
+  enum reg_class best_class = NO_REGS;
+  unsigned int best_size = 0;
+  int cost;
+
+  for (rclass = 1; rclass < N_REG_CLASSES; rclass++)
+    {
+      int bad = 0;
+      for (regno = 0; regno < FIRST_PSEUDO_REGISTER && !bad; regno++)
+	if (TEST_HARD_REG_BIT (reg_class_contents[rclass], regno)
+	    && !HARD_REGNO_MODE_OK (regno, mode))
+	  bad = 1;
+
+      if (bad)
+	continue;
+
+      cost = register_move_cost (outer, (enum reg_class) rclass, dest_class);
+
+      if ((reg_class_size[rclass] > best_size
+	   && (best_cost < 0 || best_cost >= cost))
+	  || best_cost > cost)
+	{
+	  best_class = (enum reg_class) rclass;
+	  best_size = reg_class_size[rclass];
+	  best_cost = register_move_cost (outer, (enum reg_class) rclass,
+					  dest_class);
+	}
+    }
+
+  gcc_assert (best_size != 0);
+
+#ifdef LIMIT_RELOAD_CLASS
+  best_class = LIMIT_RELOAD_CLASS (mode, best_class);
+#endif
+  return best_class;
+}
 
 /* Return the number of a previously made reload that can be combined with
    a new one, or n_reloads if none of the existing reloads can be used.
@@ -925,6 +974,8 @@  push_reload (rtx in, rtx out, rtx *inloc
   int secondary_in_reload = -1, secondary_out_reload = -1;
   enum insn_code secondary_in_icode = CODE_FOR_nothing;
   enum insn_code secondary_out_icode = CODE_FOR_nothing;
+  enum reg_class subreg_in_class ATTRIBUTE_UNUSED;
+  subreg_in_class = NO_REGS;
 
   /* INMODE and/or OUTMODE could be VOIDmode if no mode
      has been specified for the operand.  In that case,
@@ -1091,16 +1142,18 @@  push_reload (rtx in, rtx out, rtx *inloc
 
   if (in != 0 && reload_inner_reg_of_subreg (in, inmode, false))
     {
-      enum reg_class in_class = rclass;
-
       if (REG_P (SUBREG_REG (in)))
-	in_class
+	subreg_in_class
 	  = find_valid_class (inmode, GET_MODE (SUBREG_REG (in)),
 			      subreg_regno_offset (REGNO (SUBREG_REG (in)),
 						   GET_MODE (SUBREG_REG (in)),
 						   SUBREG_BYTE (in),
 						   GET_MODE (in)),
 			      REGNO (SUBREG_REG (in)));
+      else if (GET_CODE (SUBREG_REG (in)) == SYMBOL_REF)
+	subreg_in_class = find_valid_class_1 (inmode,
+					      GET_MODE (SUBREG_REG (in)),
+					      rclass);
 
       /* This relies on the fact that emit_reload_insns outputs the
 	 instructions for input reloads of type RELOAD_OTHER in the same
@@ -1108,7 +1161,7 @@  push_reload (rtx in, rtx out, rtx *inloc
 	 RELOAD_OTHER, we are guaranteed that this inner reload will be
 	 output before the outer reload.  */
       push_reload (SUBREG_REG (in), NULL_RTX, &SUBREG_REG (in), (rtx *) 0,
-		   in_class, VOIDmode, VOIDmode, 0, 0, opnum, type);
+		   subreg_in_class, VOIDmode, VOIDmode, 0, 0, opnum, type);
       dont_remove_subreg = 1;
     }
 
@@ -1327,13 +1380,15 @@  push_reload (rtx in, rtx out, rtx *inloc
 	 So add an additional reload.  */
 
 #ifdef SECONDARY_MEMORY_NEEDED
-      /* If a memory location is needed for the copy, make one.  */
-      if (in != 0
+      if (subreg_in_class == NO_REGS
+	  && in != 0
 	  && (REG_P (in)
 	      || (GET_CODE (in) == SUBREG && REG_P (SUBREG_REG (in))))
-	  && reg_or_subregno (in) < FIRST_PSEUDO_REGISTER
-	  && SECONDARY_MEMORY_NEEDED (REGNO_REG_CLASS (reg_or_subregno (in)),
-				      rclass, inmode))
+	  && reg_or_subregno (in) < FIRST_PSEUDO_REGISTER)
+	subreg_in_class = REGNO_REG_CLASS (reg_or_subregno (in));
+      /* If a memory location is needed for the copy, make one.  */
+      if (subreg_in_class != NO_REGS
+	  && SECONDARY_MEMORY_NEEDED (subreg_in_class, rclass, inmode))
 	get_secondary_mem (in, inmode, opnum, type);
 #endif
 
Index: gcc/testsuite/gcc.c-torture/compile/20120727-1.c
===================================================================
--- gcc/testsuite/gcc.c-torture/compile/20120727-1.c	(revision 0)
+++ gcc/testsuite/gcc.c-torture/compile/20120727-1.c	(revision 0)
@@ -0,0 +1,11 @@ 
+union {
+  char *p;
+  float f;
+} u;
+
+void
+f (void)
+{
+  u.p = "";
+  u.f += 1.1;
+}
Index: gcc/config/i386/i386.h
===================================================================
--- gcc/config/i386/i386.h	(revision 189284)
+++ gcc/config/i386/i386.h	(working copy)
@@ -1376,7 +1376,8 @@  enum reg_class
   ((MODE) == QImode && !TARGET_64BIT				\
    && ((CLASS) == ALL_REGS || (CLASS) == GENERAL_REGS		\
        || (CLASS) == LEGACY_REGS || (CLASS) == INDEX_REGS)	\
-   ? Q_REGS : (CLASS))
+   ? Q_REGS							\
+   : (CLASS) == INT_SSE_REGS ? GENERAL_REGS : (CLASS))
 
 /* If we are copying between general and FP registers, we need a memory
    location. The same is true for SSE and MMX registers.  */
Index: gcc/reload1.c
===================================================================
--- gcc/reload1.c	(revision 189284)
+++ gcc/reload1.c	(working copy)
@@ -8468,6 +8468,18 @@  emit_insn_if_valid_for_reload (rtx insn)
   return NULL;
 }
 
+/* If X is not a subreg, return it unmodified.  If it is a subreg,
+   look up whether we made a replacement for the SUBREG_REG.  Return
+   either the replacement or the SUBREG_REG.  */
+
+static rtx
+replaced_subreg (rtx x)
+{
+  if (GET_CODE (x) == SUBREG)
+    return find_replacement (&SUBREG_REG (x));
+  return x;
+}
+
 /* Emit code to perform a reload from IN (which may be a reload register) to
    OUT (which may also be a reload register).  IN or OUT is from operand
    OPNUM with reload type TYPE.
@@ -8478,7 +8490,7 @@  static rtx
 gen_reload (rtx out, rtx in, int opnum, enum reload_type type)
 {
   rtx last = get_last_insn ();
-  rtx tem;
+  rtx tem, tem1, tem2;
 
   /* If IN is a paradoxical SUBREG, remove it and try to put the
      opposite SUBREG on OUT.  Likewise for a paradoxical SUBREG on OUT.  */
@@ -8615,14 +8627,12 @@  gen_reload (rtx out, rtx in, int opnum,
 
 #ifdef SECONDARY_MEMORY_NEEDED
   /* If we need a memory location to do the move, do it that way.  */
-  else if ((REG_P (in)
-            || (GET_CODE (in) == SUBREG && REG_P (SUBREG_REG (in))))
-	   && reg_or_subregno (in) < FIRST_PSEUDO_REGISTER
-	   && (REG_P (out)
-	       || (GET_CODE (out) == SUBREG && REG_P (SUBREG_REG (out))))
-	   && reg_or_subregno (out) < FIRST_PSEUDO_REGISTER
-	   && SECONDARY_MEMORY_NEEDED (REGNO_REG_CLASS (reg_or_subregno (in)),
-				       REGNO_REG_CLASS (reg_or_subregno (out)),
+  else if ((tem1 = replaced_subreg (in), tem2 = replaced_subreg (out),
+	    (REG_P (tem1) && REG_P (tem2)))
+	   && REGNO (tem1) < FIRST_PSEUDO_REGISTER
+	   && REGNO (tem2) < FIRST_PSEUDO_REGISTER
+	   && SECONDARY_MEMORY_NEEDED (REGNO_REG_CLASS (REGNO (tem1)),
+				       REGNO_REG_CLASS (REGNO (tem2)),
 				       GET_MODE (out)))
     {
       /* Get the memory to use and rewrite both registers to its mode.  */