* fold-const.c (fold): Transform (c1 - x) cmp c2, where cmp is a

	comparison operation and c1/c2 are floating point constants into
	x swap(cmp) (c1 - c2).

	* gcc.dg/20030414-2.c: New test case.


git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@65584 138bc75d-0d04-0410-961f-82ee72b054a4

4 files changed, 62 insertions, 1 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 05b01f98a32..bf118416c75 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,9 @@
+2003-04-14  Roger Sayle  <roger@eyesopen.com>
+
+	* fold-const.c (fold):  Transform (c1 - x) cmp c2, where cmp is a
+	comparison operation and c1/c2 are floating point constants into
+	x swap(cmp) (c1 - c2).
+
 2003-04-14  Vladimir Makarov  <vmakarov@redhat.com>
 
 	* genautomata.c (output_translate_vect): Fix a typo in loop
@@ -1376,7 +1382,7 @@ Thu Apr  3 00:18:49 CEST 2003  Jan Hubicka  <jh@suse.cz>
 2003-04-01  Roger Sayle  <roger@eyesopen.com>
 
 	PR fortran/9974
-	* gcse.c (reg_killed_on_egde): New function to test whether the
+	* gcse.c (reg_killed_on_edge): New function to test whether the
 	given reg is overwritten by any instruction queued on an edge.
 	(bypass_block): Ignore substitutions killed on incoming edges.
 	Don't bypass outgoing edges that have queued instructions.
diff --git a/gcc/fold-const.c b/gcc/fold-const.c
index ebb87e27a5e..95812a2e13c 100644
--- a/gcc/fold-const.c
+++ b/gcc/fold-const.c
@@ -6484,6 +6484,19 @@ fold (expr)
 	      && ! TREE_CONSTANT_OVERFLOW (tem))
 	    return fold (build (code, type, TREE_OPERAND (arg0, 0), tem));
 
+	  /* Likewise, we can simplify a comparison of a real constant with
+	     a MINUS_EXPR whose first operand is also a real constant, i.e.
+	     (c1 - x) < c2 becomes x > c1-c2.  */
+	  if (flag_unsafe_math_optimizations
+	      && TREE_CODE (arg1) == REAL_CST
+	      && TREE_CODE (arg0) == MINUS_EXPR
+	      && TREE_CODE (TREE_OPERAND (arg0, 0)) == REAL_CST
+	      && 0 != (tem = const_binop (MINUS_EXPR, TREE_OPERAND (arg0, 0),
+					  arg1, 0))
+	      && ! TREE_CONSTANT_OVERFLOW (tem))
+	    return fold (build (swap_tree_comparison (code), type,
+				TREE_OPERAND (arg0, 1), tem));
+
 	  /* Fold comparisons against built-in math functions.  */
 	  if (TREE_CODE (arg1) == REAL_CST
 	      && flag_unsafe_math_optimizations
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 214ed1a2075..1fc22eecce1 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,7 @@
+2003-04-14  Roger Sayle  <roger@eyesopen.com>
+
+	* gcc.dg/20030414-2.c: New test case.
+
 2003-04-14  Hans-Peter Nilsson  <hp@axis.com>
 
 	PR target/10377
diff --git a/gcc/testsuite/gcc.dg/20030414-2.c b/gcc/testsuite/gcc.dg/20030414-2.c
new file mode 100644
index 00000000000..f4eb8bf36ec
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/20030414-2.c
@@ -0,0 +1,38 @@
+/* Copyright (C) 2003 Free Software Foundation.
+
+   Check that constant folding (c1 - x) op c2 into x swap(op) c1-c2
+   doesn't break anything.
+
+   Written by Roger Sayle, 27th March 2003.  */
+
+/* { dg-do run } */
+/* { dg-options "-O2 -ffast-math" } */
+
+extern void abort (void);
+
+int foo(double x)
+{
+  return (10.0 - x) > 3.0;
+}
+
+int bar (double x)
+{
+  return (10.0 - x) == 5.0;
+}
+
+int main()
+{
+  if (foo (8.0))
+    abort ();
+
+  if (! foo (6.0))
+    abort ();
+
+  if (bar (1.0))
+    abort ();
+
+  if (! bar (5.0))
+    abort ();
+  return 0;
+}
+