fold-const.c (fold_binary_loc): Fold (X * CST1) & CST2 to zero or to (X * CST1) ...

2012-05-08  Richard Guenther  <rguenther@suse.de>

	* fold-const.c (fold_binary_loc): Fold (X * CST1) & CST2
	to zero or to (X * CST1) & CST2' when CST1 has trailing zeros.

	* gcc.dg/fold-bitand-4.c: New testcase.

From-SVN: r187280

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index a140b83847b61a447e639d68693885bb0c741188..b71e988e1003a5681e8e2c17f59d774f78db2a98 100644 (file)
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,8 @@
+2012-05-08  Richard Guenther  <rguenther@suse.de>
+
+       * fold-const.c (fold_binary_loc): Fold (X * CST1) & CST2
+       to zero or to (X * CST1) & CST2' when CST1 has trailing zeros.
+
 2012-05-08  Georg-Johann Lay  <avr@gjlay.de>
 
        * Makefile.in (TEXI_GCC_FILES): Add avr-mmcu.texi.

diff --git a/gcc/fold-const.c b/gcc/fold-const.c
index f8b31b7d1134d969dbb3d0beb58458cb7a54adfb..5bb75d490d9845e172c5c28a70d18c8fdf446817 100644 (file)
--- a/gcc/fold-const.c
+++ b/gcc/fold-const.c
@@ -11449,6 +11449,30 @@ fold_binary_loc (location_t loc,
            return fold_convert_loc (loc, type, arg0);
        }
 
+      /* Fold (X * CST1) & CST2 to zero if we can, or drop known zero
+         bits from CST2.  */
+      if (TREE_CODE (arg1) == INTEGER_CST
+         && TREE_CODE (arg0) == MULT_EXPR
+         && TREE_CODE (TREE_OPERAND (arg0, 1)) == INTEGER_CST)
+       {
+         int arg1tz
+           = double_int_ctz (tree_to_double_int (TREE_OPERAND (arg0, 1)));
+         if (arg1tz > 0)
+           {
+             double_int arg1mask, masked;
+             arg1mask = double_int_not (double_int_mask (arg1tz));
+             arg1mask = double_int_ext (arg1mask, TYPE_PRECISION (type),
+                                        TYPE_UNSIGNED (type));
+             masked = double_int_and (arg1mask, tree_to_double_int (arg1));
+             if (double_int_zero_p (masked))
+               return omit_two_operands_loc (loc, type, build_zero_cst (type),
+                                             arg0, arg1);
+             else if (!double_int_equal_p (masked, tree_to_double_int (arg1)))
+               return fold_build2_loc (loc, code, type, op0,
+                                       double_int_to_tree (type, masked));
+           }
+       }
+
       /* For constants M and N, if M == (1LL << cst) - 1 && (N & M) == M,
         ((A & N) + B) & M -> (A + B) & M
         Similarly if (N & M) == 0,

diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index f9ef02a8278f045bf013c40a12c7b7da00962078..ca4bcf89c6e4ffacac5b35eb2ebb6689f959aa7c 100644 (file)
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,7 @@
+2012-05-08  Richard Guenther  <rguenther@suse.de>
+
+       * gcc.dg/fold-bitand-4.c: New testcase.
+
 2012-05-08  Dehao Chen  <dehao@google.com>
 
        * gcc.dg/predict-1.c: Check if LOOP_IV_COMPARE static predict

diff --git a/gcc/testsuite/gcc.dg/fold-bitand-4.c b/gcc/testsuite/gcc.dg/fold-bitand-4.c
new file mode 100644 (file)
index 0000000..dba8361
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/fold-bitand-4.c
@@ -0,0 +1,16 @@
+/* { dg-do compile } */
+/* { dg-options "-O -fdump-tree-original" } */
+
+int foo (int i)
+{
+  return (i * 8) & 5;
+}
+
+unsigned bar (unsigned i)
+{
+  return (i * 6) & 5;
+}
+
+/* { dg-final { scan-tree-dump-times "\\\&" 1 "original" } } */
+/* { dg-final { scan-tree-dump-times "\\\& 4;" 1 "original" } } */
+/* { dg-final { cleanup-tree-dump "original" } } */