re PR middle-end/31029 (Fold does not fold C - a == a)

2009-03-31  Richard Guenther  <rguenther@suse.de>

	PR middle-end/31029
	* fold-const.c (fold_binary): Fold X +- Y CMP X to Y CMP 0 for
	equality comparisons.  Fold C - X CMP X if C % 2 == 1.

	* gcc.dg/fold-compare-4.c: New testcase.
	* gcc.dg/fold-compare-5.c: Likewise.

From-SVN: r145345

5 files changed, 77 insertions, 11 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 0f81767..e389951 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,5 +1,11 @@
 2009-03-31  Richard Guenther  <rguenther@suse.de>
 
+	PR middle-end/31029
+	* fold-const.c (fold_binary): Fold X +- Y CMP X to Y CMP 0 for
+	equality comparisons.  Fold C - X CMP X if C % 2 == 1.
+
+2009-03-31  Richard Guenther  <rguenther@suse.de>
+
 	* tree.h (div_if_zero_remainder): Declare.
 	* fold-const.c (div_if_zero_remainder): Export.
 	* tree-ssa-forwprop.c
diff --git a/gcc/fold-const.c b/gcc/fold-const.c
index 4951600..ec06954 100644
--- a/gcc/fold-const.c
+++ b/gcc/fold-const.c
@@ -12191,22 +12191,33 @@ fold_binary (enum tree_code code, tree type, tree op0, tree op1)
 					 fold_convert (TREE_TYPE (arg0), arg1),
 					 TREE_OPERAND (arg0, 1)));
 
-      /* Transform comparisons of the form X +- C CMP X.  */
-      if ((TREE_CODE (arg0) == PLUS_EXPR || TREE_CODE (arg0) == MINUS_EXPR)
+      /* Transform comparisons of the form X +- Y CMP X to Y CMP 0.  */
+      if ((TREE_CODE (arg0) == PLUS_EXPR
+	   || TREE_CODE (arg0) == POINTER_PLUS_EXPR
+	   || TREE_CODE (arg0) == MINUS_EXPR)
 	  && operand_equal_p (TREE_OPERAND (arg0, 0), arg1, 0)
-	  && TREE_CODE (TREE_OPERAND (arg0, 1)) == INTEGER_CST
 	  && (INTEGRAL_TYPE_P (TREE_TYPE (arg0))
 	      || POINTER_TYPE_P (TREE_TYPE (arg0))))
 	{
-	  tree cst = TREE_OPERAND (arg0, 1);
+	  tree val = TREE_OPERAND (arg0, 1);
+	  return omit_two_operands (type,
+				    fold_build2 (code, type,
+						 val,
+						 build_int_cst (TREE_TYPE (val),
+								0)),
+				    TREE_OPERAND (arg0, 0), arg1);
+	}
 
-	  if (code == EQ_EXPR
-	      && !integer_zerop (cst))
-	    return omit_two_operands (type, boolean_false_node,
-				      TREE_OPERAND (arg0, 0), arg1);
-	  else
-	    return omit_two_operands (type, boolean_true_node,
-				      TREE_OPERAND (arg0, 0), arg1);
+      /* Transform comparisons of the form C - X CMP X if C % 2 == 1.  */
+      if (TREE_CODE (arg0) == MINUS_EXPR
+	  && TREE_CODE (TREE_OPERAND (arg0, 0)) == INTEGER_CST
+	  && operand_equal_p (TREE_OPERAND (arg0, 1), arg1, 0)
+	  && (TREE_INT_CST_LOW (TREE_OPERAND (arg0, 0)) & 1) == 1)
+	{
+	  return omit_two_operands (type,
+				    code == NE_EXPR
+				    ? boolean_true_node : boolean_false_node,
+				    TREE_OPERAND (arg0, 1), arg1);
 	}
 
       /* If we have X - Y == 0, we can convert that to X == Y and similarly
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 9b1aef3..19cf3d6 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,5 +1,11 @@
 2009-03-31  Richard Guenther  <rguenther@suse.de>
 
+	PR middle-end/31029
+	* gcc.dg/fold-compare-4.c: New testcase.
+	* gcc.dg/fold-compare-5.c: Likewise.
+
+2009-03-31  Richard Guenther  <rguenther@suse.de>
+
 	* gcc.dg/tree-ssa/forwprop-12.c: New testcase.
 
 2009-03-31  Joseph Myers  <joseph@codesourcery.com>
diff --git a/gcc/testsuite/gcc.dg/fold-compare-4.c b/gcc/testsuite/gcc.dg/fold-compare-4.c
new file mode 100644
index 0000000..d4bb64a
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/fold-compare-4.c
@@ -0,0 +1,23 @@
+/* { dg-do compile } */
+/* { dg-options "-fdump-tree-original" } */
+
+int test1 (int a, int b)
+{
+  return a - b == a;
+}
+int test2 (int a, int b)
+{
+  return a + b == a;
+}
+int test3 (int a)
+{
+  return a + 5 == a;
+}
+int test4 (int a)
+{
+  return a - 5 == a;
+}
+
+/* { dg-final { scan-tree-dump-times "b == 0" 2 "original" } } */
+/* { dg-final { scan-tree-dump-times "return 0" 2 "original" } } */
+/* { dg-final { cleanup-tree-dump "original" } } */
diff --git a/gcc/testsuite/gcc.dg/fold-compare-5.c b/gcc/testsuite/gcc.dg/fold-compare-5.c
new file mode 100644
index 0000000..9ec8c33
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/fold-compare-5.c
@@ -0,0 +1,20 @@
+/* { dg-do compile } */
+/* { dg-options "-fdump-tree-original" } */
+
+int test1 (int a)
+{
+  return 2 - a == a;
+}
+int test2 (int a)
+{
+  return 1 - a == a;
+}
+int test3 (int a)
+{
+  return 1 - a != a;
+}
+
+/* { dg-final { scan-tree-dump-times "return 2 - a == a" 1 "original" } } */
+/* { dg-final { scan-tree-dump-times "return 0" 1 "original" } } */
+/* { dg-final { scan-tree-dump-times "return 1" 1 "original" } } */
+/* { dg-final { cleanup-tree-dump "original" } } */