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

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 90061ec7f5a87aa184cd559caca0c154421809eb..207d68088d3965e6d0d560219fcb96c7aca37e7f 100644 (file)
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,9 @@
+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>
 

diff --git a/gcc/fold-const.c b/gcc/fold-const.c
index 9d249cc3b2fcbe57819c60caeaed950ea197f290..e7a4b8c8f49556d7fe9634935902a0bc0f194040 100644 (file)
--- a/gcc/fold-const.c
+++ b/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));

diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 9c89203d503b65436858adfd7dd02546c69af290..2bfa419d8031ae2798280fb94b871126a5b25662 100644 (file)
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+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.

diff --git a/gcc/testsuite/gcc.dg/pr19988.c b/gcc/testsuite/gcc.dg/pr19988.c
new file mode 100644 (file)
index 0000000..aa2fed1
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr19988.c
@@ -0,0 +1,14 @@
+/* { 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" } } */