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[PATCH, Fix PR 31098] a*C == b*C is not foldded to a == b with --fast-math/floating point


Hi,
Could somebody please review this patch which is a proposed fix for PR 31098.


2007-10-07 Pranav Bhandarkar <pranav.bhandarkar@celunite.com>

  * fold-const.c (fold_comparison): fold (a OP c) CMP (b OP c) -> a
  CMP b, iff c is not zero
  * testsuite/pr31098.c: New

Thanks,
Pranav

--
Pranav Bhandarkar
GNU Tools
Celunite, Inc.
(www.celunite.com)
+91-98220 82881

Index: fold-const.c
===================================================================
--- fold-const.c	(revision 128907)
+++ fold-const.c	(working copy)
@@ -9048,6 +9048,23 @@
 	return fold_build2 (code, type, TREE_OPERAND (arg1, 0),
 			    TREE_OPERAND (arg0, 0));
 
+      /* (a OP c) CMP (b OP c) -> a CMP b, iff c is not zero */
+      if (fast_math_flags_set_p () && (TREE_CODE (arg0) == TREE_CODE (arg1)) 
+	  && BINARY_CLASS_P (arg0) && !real_zerop (TREE_OPERAND (arg0,1)))
+	{
+	  if (TREE_CODE (TREE_OPERAND (arg0, 1)) == REAL_CST
+	      && TREE_CODE (TREE_OPERAND (arg1, 1)) == REAL_CST )
+	    {
+	      REAL_VALUE_TYPE *cst0, *cst1;
+	      cst0 = &TREE_REAL_CST (TREE_OPERAND (arg0, 1));
+	      cst1 = &TREE_REAL_CST (TREE_OPERAND (arg1, 1));
+	      
+	      if (real_compare (EQ_EXPR, cst0, cst1))
+		return fold_build2 (code, type, TREE_OPERAND (arg0,0), TREE_OPERAND (arg1,0));
+
+	    }
+	}
+
       if (TREE_CODE (arg1) == REAL_CST)
 	{
 	  REAL_VALUE_TYPE cst;
--- /dev/null	2006-05-22 19:55:23.000000000 +0530
+++ pr31098.c	2007-10-07 21:01:37.000000000 +0530
@@ -0,0 +1,11 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-original --fast-math" } */
+
+int f(float a, float b)
+{
+  return a*10 == b*10;
+}
+
+
+/* { dg-final { scan-tree-dump-times "return a == b" 1 "original" } } */
+/* { dg-final { cleanup-tree-dump "original" } } */

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