re PR middle-end/23673 (fold does not fold (a^b) != 0 to a != b)

	PR middle-end/23673
	* fold-const.c (fold_binary) <EQ_EXPR>:  Fold (X^Y) == 0 as X == Y
	and (X^Y) != 0 as X != Y.  Fold (X^Y) == Y as X == 0, and some
	symmetry related transformations.  Fold (X^C1) == C2 as
	X == (C1^C2).

	* gcc.dg/fold-eqxor-1.c: New test case.
	* gcc.dg/fold-eqxor-2.c: Likewise.
	* gcc.dg/fold-eqxor-3.c: Likewise.

From-SVN: r111442

6 files changed, 125 insertions, 0 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 2c42abf..b2abdce 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,11 @@
+2006-02-25  Roger Sayle  <roger@eyesopen.com>
+
+	PR middle-end/23673
+	* fold-const.c (fold_binary) <EQ_EXPR>:  Fold (X^Y) == 0 as X == Y
+	and (X^Y) != 0 as X != Y.  Fold (X^Y) == Y as X == 0, and some
+	symmetry related transformations.  Fold (X^C1) == C2 as
+	X == (C1^C2).
+
 2006-02-25  Juergen Weigert  <jw@suse.de>
 	Richard Guenther  <rguenther@suse.de>
 
diff --git a/gcc/fold-const.c b/gcc/fold-const.c
index 04a8fab..3c3852b 100644
--- a/gcc/fold-const.c
+++ b/gcc/fold-const.c
@@ -9767,6 +9767,32 @@ fold_binary (enum tree_code code, tree type, tree op0, tree op1)
 	    }
 	}
 
+      /* (X ^ Y) == 0 becomes X == Y, and (X ^ Y) != 0 becomes X != Y.  */
+      if (integer_zerop (arg1)
+	  && TREE_CODE (arg0) == BIT_XOR_EXPR)
+	return fold_build2 (code, type, TREE_OPERAND (arg0, 0),
+			    TREE_OPERAND (arg0, 1));
+
+      /* (X ^ Y) == Y becomes X == 0.  We know that Y has no side-effects.  */
+      if (TREE_CODE (arg0) == BIT_XOR_EXPR
+	  && operand_equal_p (TREE_OPERAND (arg0, 1), arg1, 0))
+	return fold_build2 (code, type, TREE_OPERAND (arg0, 0),
+			    build_int_cst (TREE_TYPE (arg1), 0));
+      /* Likewise (X ^ Y) == X becomes Y == 0.  X has no side-effects.  */
+      if (TREE_CODE (arg0) == BIT_XOR_EXPR
+	  && operand_equal_p (TREE_OPERAND (arg0, 0), arg1, 0)
+	  && reorder_operands_p (TREE_OPERAND (arg0, 1), arg1))
+	return fold_build2 (code, type, TREE_OPERAND (arg0, 1),
+			    build_int_cst (TREE_TYPE (arg1), 0));
+
+      /* (X ^ C1) op C2 can be rewritten as X op (C1 ^ C2).  */
+      if (TREE_CODE (arg0) == BIT_XOR_EXPR
+	  && TREE_CODE (arg1) == INTEGER_CST
+	  && TREE_CODE (TREE_OPERAND (arg0, 1)) == INTEGER_CST)
+	return fold_build2 (code, type, TREE_OPERAND (arg0, 0),
+			    fold_build2 (BIT_XOR_EXPR, TREE_TYPE (arg1),
+					 TREE_OPERAND (arg0, 1), arg1));
+
       if (integer_zerop (arg1)
 	  && tree_expr_nonzero_p (arg0))
         {
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 387e690..9656f4e 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,10 @@
+2006-02-25  Roger Sayle  <roger@eyesopen.com>
+
+	PR middle-end/23673
+	* gcc.dg/fold-eqxor-1.c: New test case.
+	* gcc.dg/fold-eqxor-2.c: Likewise.
+	* gcc.dg/fold-eqxor-3.c: Likewise.
+
 2006-02-25  Thomas Koenig  <Thomas.Koenig@online.de>
 
 	PR fortran/23092
diff --git a/gcc/testsuite/gcc.dg/fold-eqxor-1.c b/gcc/testsuite/gcc.dg/fold-eqxor-1.c
new file mode 100644
index 0000000..d220e42
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/fold-eqxor-1.c
@@ -0,0 +1,28 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-original" } */
+
+int test1(int a, int b)
+{
+  return (a ^ b) == 0;
+}
+
+int test2(int c, int d)
+{
+  return (c ^ d) != 0;
+}
+
+unsigned int test3(unsigned int e, unsigned int f)
+{
+  return (e ^ f) == 0;
+}
+
+unsigned int test4(unsigned int g, unsigned int h)
+{
+  return (g ^ h) != 0;
+}
+
+/* { dg-final { scan-tree-dump-times "a == b" 1 "original" } } */
+/* { dg-final { scan-tree-dump-times "c != d" 1 "original" } } */
+/* { dg-final { scan-tree-dump-times "e == f" 1 "original" } } */
+/* { dg-final { scan-tree-dump-times "g != h" 1 "original" } } */
+/* { dg-final { cleanup-tree-dump "original" } } */
diff --git a/gcc/testsuite/gcc.dg/fold-eqxor-2.c b/gcc/testsuite/gcc.dg/fold-eqxor-2.c
new file mode 100644
index 0000000..ee5ec9fa
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/fold-eqxor-2.c
@@ -0,0 +1,28 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-original" } */
+
+int test1(int a, int b)
+{
+  return (a ^ b) == a;
+}
+
+int test2(int c, int d)
+{
+  return (c ^ d) != c;
+}
+
+int test3(int e, int f)
+{
+  return (e ^ f) == f;
+}
+
+int test4(int g, int h)
+{
+  return (g ^ h) != h;
+}
+
+/* { dg-final { scan-tree-dump-times "b == 0" 1 "original" } } */
+/* { dg-final { scan-tree-dump-times "d != 0" 1 "original" } } */
+/* { dg-final { scan-tree-dump-times "e == 0" 1 "original" } } */
+/* { dg-final { scan-tree-dump-times "g != 0" 1 "original" } } */
+/* { dg-final { cleanup-tree-dump "original" } } */
diff --git a/gcc/testsuite/gcc.dg/fold-eqxor-3.c b/gcc/testsuite/gcc.dg/fold-eqxor-3.c
new file mode 100644
index 0000000..a087375
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/fold-eqxor-3.c
@@ -0,0 +1,28 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-original" } */
+
+int test1(int a, int b)
+{
+  return (a ^ 2) == 2;
+}
+
+int test2(int c, int d)
+{
+  return (c ^ 4) != 4;
+}
+
+int test3(int e, int f)
+{
+  return (e ^ 2) == 6;
+}
+
+int test4(int g, int h)
+{
+  return (g ^ 6) != 4;
+}
+
+/* { dg-final { scan-tree-dump-times "a == 0" 1 "original" } } */
+/* { dg-final { scan-tree-dump-times "c != 0" 1 "original" } } */
+/* { dg-final { scan-tree-dump-times "e == 4" 1 "original" } } */
+/* { dg-final { scan-tree-dump-times "g != 2" 1 "original" } } */
+/* { dg-final { cleanup-tree-dump "original" } } */