re PR middle-end/19988 (pessimizes fp multiply-add/subtract combo)

2010-01-21  Richard Guenther  <rguenther@suse.de>

	PR middle-end/19988
	* fold-const.c (negate_expr_p): Pretend only negative
	real constants are easily negatable.

	* gcc.dg/pr19988.c: New testcase.

From-SVN: r156152

gcc/ChangeLog

+2010-01-21  Richard Guenther  <rguenther@suse.de>
+
+	PR middle-end/19988
+	* fold-const.c (negate_expr_p): Pretend only negative
+	real constants are easily negatable.
+
 2010-01-20  Janis Johnson  <janis187@us.ibm.com>
 	    Jason Merrill  <jason@redhat.com>
 

gcc/fold-const.c

@@ -1129,10 +1129,14 @@ negate_expr_p (tree t)
 	      && TYPE_OVERFLOW_WRAPS (type));
 
     case FIXED_CST:
-    case REAL_CST:
     case NEGATE_EXPR:
       return true;
 
+    case REAL_CST:
+      /* We want to canonicalize to positive real constants.  Pretend
+         that only negative ones can be easily negated.  */
+      return REAL_VALUE_NEGATIVE (TREE_REAL_CST (t));
+
     case COMPLEX_CST:
       return negate_expr_p (TREE_REALPART (t))
 	     && negate_expr_p (TREE_IMAGPART (t));

gcc/testsuite/ChangeLog

+2010-01-21  Richard Guenther  <rguenther@suse.de>
+
+	PR middle-end/19988
+	* gcc.dg/pr19988.c: New testcase.
+
 2010-01-20  Janis Johnson  <janis187@us.ibm.com>
 
 	* g++.dg/compat/decimal/compat-common.h: New file.

gcc/testsuite/gcc.dg/pr19988.c

+/* { dg-do compile } */
+/* { dg-options "-O -fdump-tree-optimized -fdump-tree-original" } */
+
+double foo(double x, double y)
+{
+  return ((x + 0.1234 * y) * (x - 0.1234 * y));
+}
+
+/* Keep positive constants during folding.  */
+/* { dg-final { scan-tree-dump-times " 1.23" 2 "original" } } */
+/* CSE one multiplication.  */
+/* { dg-final { scan-tree-dump-times " \\\* " 2 "optimized" } } */
+/* { dg-final { cleanup-tree-dump "original" } } */
+/* { dg-final { cleanup-tree-dump "optimized" } } */