fold_const (fold_binary): Fold X % (2**N) to X & (2**N - 1) for nonnegative values of X.

2005-06-18  James A. Morrison  <phython@gcc.gnu.org>

        * fold_const (fold_binary): Fold X % (2**N) to X & (2**N - 1) for
        nonnegative values of X.

From-SVN: r101163

gcc/ChangeLog

+2005-06-18  James A. Morrison  <phython@gcc.gnu.org>
+
+	* fold_const (fold_binary): Fold X % (2**N) to X & (2**N - 1) for
+	nonnegative values of X.
+
 2005-06-18  Uros Bizjak  <uros@kss-loka.si>
 
 	* doc/md.texi (Standard Names): Change insn pattern name

gcc/fold-const.c

@@ -8337,11 +8337,11 @@ fold_binary (enum tree_code code, tree type, tree op0, tree op1)
 	  && TREE_INT_CST_HIGH (arg1) == -1)
 	return omit_one_operand (type, integer_zero_node, arg0);
 
-      /* Optimize unsigned TRUNC_MOD_EXPR by a power of two into a
-	 BIT_AND_EXPR, i.e. "X % C" into "X & C2".  */
-      if (code == TRUNC_MOD_EXPR
-	  && TYPE_UNSIGNED (type)
-	  && integer_pow2p (arg1))
+      /* Optimize TRUNC_MOD_EXPR by a power of two into a BIT_AND_EXPR,
+         i.e. "X % C" into "X & C2", if X and C are positive.  */
+      if ((code == TRUNC_MOD_EXPR || code == FLOOR_MOD_EXPR)
+	  && (TYPE_UNSIGNED (type) || tree_expr_nonnegative_p (arg0))
+	  && integer_pow2p (arg1) && tree_int_cst_sgn (arg1) >= 0)
 	{
 	  unsigned HOST_WIDE_INT high, low;
 	  tree mask;

gcc/testsuite/ChangeLog

+2005-06-18  James A Morrison  <phython@gcc.gnu.org>
+
+	* gcc.dg/fold-mod-1.c: New test.
+
 2005-06-18  Steven G. Kargl  <kargls@comcast.net>
 
 	PR fortran/19926

gcc/testsuite/gcc.dg/fold-mod-1.c

+/* { dg-do compile } */
+/* { dg-options "-fdump-tree-gimple" } */
+
+#define ABS(x) (x > 0 ? x : -x)
+
+unsigned int f (unsigned int a) {
+	/* (unsigned)-8 is not a power of 2.  */
+	return a % -8;
+}
+
+int g (int b) {
+	return ABS (b) % -8;
+}
+
+int h (int c) {
+	return ABS (c) % 8;
+}
+
+unsigned int k (unsigned int d) {
+	return d % 8;
+}
+
+/* { dg-final { scan-tree-dump "a % 4294967288" "gimple" } } */
+/* { dg-final { scan-tree-dump-times " & 7" 3 "gimple" } } */
+/* { dg-final { cleanup-tree-dump "gimple" } } */