2006-10-21 Richard Guenther <rguenther@suse.de>

	PR middle-end/26898
	* fold-const.c (fold_comparison): Fold signed comparisons
	of the form X +- C1 CMP Y +- C2.

	* gcc.dg/torture/pr26898-1.c: New testcase.
	* gcc.dg/torture/pr26898-2.c: Likewise.


git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@117931 138bc75d-0d04-0410-961f-82ee72b054a4

5 files changed, 80 insertions, 0 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 0bb59aab9b1..fdaa244cfe5 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,5 +1,11 @@
 2006-10-21  Richard Guenther  <rguenther@suse.de>
 
+	PR middle-end/26898
+	* fold-const.c (fold_comparison): Fold signed comparisons
+	of the form X +- C1 CMP Y +- C2.
+
+2006-10-21  Richard Guenther  <rguenther@suse.de>
+
 	PR target/19116
 	* config/i386/i386.c (override_options): Do not set MASK_IEEE_FP
 	if flag_unsafe_math_optimizations is specified.  We have
diff --git a/gcc/fold-const.c b/gcc/fold-const.c
index 30efccd7ea7..b04022e1086 100644
--- a/gcc/fold-const.c
+++ b/gcc/fold-const.c
@@ -7835,6 +7835,48 @@ fold_comparison (enum tree_code code, tree type, tree op0, tree op1)
 	}
     }
 
+  /* Transform comparisons of the form X +- C1 CMP Y +- C2 to
+     X CMP Y +- C2 +- C1 for signed X, Y.  This is valid if
+     the resulting offset is smaller in absolute value than the
+     original one.  */
+  if (!(flag_wrapv || flag_trapv)
+      && !TYPE_UNSIGNED (TREE_TYPE (arg0))
+      && (TREE_CODE (arg0) == PLUS_EXPR || TREE_CODE (arg0) == MINUS_EXPR)
+      && (TREE_CODE (TREE_OPERAND (arg0, 1)) == INTEGER_CST
+	  && !TREE_OVERFLOW (TREE_OPERAND (arg0, 1)))
+      && (TREE_CODE (arg1) == PLUS_EXPR || TREE_CODE (arg1) == MINUS_EXPR)
+      && (TREE_CODE (TREE_OPERAND (arg1, 1)) == INTEGER_CST
+	  && !TREE_OVERFLOW (TREE_OPERAND (arg1, 1))))
+    {
+      tree const1 = TREE_OPERAND (arg0, 1);
+      tree const2 = TREE_OPERAND (arg1, 1);
+      tree variable1 = TREE_OPERAND (arg0, 0);
+      tree variable2 = TREE_OPERAND (arg1, 0);
+      tree cst;
+
+      /* Put the constant on the side where it doesn't overflow and is
+	 of lower absolute value than before.  */
+      cst = int_const_binop (TREE_CODE (arg0) == TREE_CODE (arg1)
+			     ? MINUS_EXPR : PLUS_EXPR,
+			     const2, const1, 0);
+      if (!TREE_OVERFLOW (cst)
+	  && tree_int_cst_compare (const2, cst) == tree_int_cst_sgn (const2))
+	return fold_build2 (code, type,
+			    variable1,
+			    fold_build2 (TREE_CODE (arg1), TREE_TYPE (arg1),
+					 variable2, cst));
+
+      cst = int_const_binop (TREE_CODE (arg0) == TREE_CODE (arg1)
+			     ? MINUS_EXPR : PLUS_EXPR,
+			     const1, const2, 0);
+      if (!TREE_OVERFLOW (cst)
+	  && tree_int_cst_compare (const1, cst) == tree_int_cst_sgn (const1))
+	return fold_build2 (code, type,
+			    fold_build2 (TREE_CODE (arg0), TREE_TYPE (arg0),
+					 variable1, cst),
+			    variable2);
+    }
+
   if (FLOAT_TYPE_P (TREE_TYPE (arg0)))
     {
       tree targ0 = strip_float_extensions (arg0);
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 8634b8e41ec..55d336cc162 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,9 @@
+2006-10-21  Richard Guenther  <rguenther@suse.de>
+
+	PR middle-end/26898
+	* gcc.dg/torture/pr26898-1.c: New testcase.
+	* gcc.dg/torture/pr26898-2.c: Likewise.
+
 2006-10-20  Lee Millward  <lee.millward@codesourcery.com>
         
         PR c++/28053
diff --git a/gcc/testsuite/gcc.dg/torture/pr26898-1.c b/gcc/testsuite/gcc.dg/torture/pr26898-1.c
new file mode 100644
index 00000000000..12ca1f38a91
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr26898-1.c
@@ -0,0 +1,14 @@
+/* { dg-do link } */
+
+#include <limits.h>
+
+extern void link_error(void);
+int main()
+{
+  int i0, i1;
+  if (!(i0 + 1 < i1 + 1 == i0 < i1))
+    link_error ();
+  if (!(i0 + INT_MIN < i1 - INT_MAX == i0 < i1 - -1))
+    link_error ();
+  return 0;
+}
diff --git a/gcc/testsuite/gcc.dg/torture/pr26898-2.c b/gcc/testsuite/gcc.dg/torture/pr26898-2.c
new file mode 100644
index 00000000000..508fde4ce7d
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr26898-2.c
@@ -0,0 +1,12 @@
+/* { dg-do run } */
+
+#include <limits.h>
+
+int a = 0, b = INT_MAX - 1;
+extern void abort(void);
+int main()
+{
+  if (a - 1 > b + 1)
+    abort();
+  return 0;
+}