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Re: [PATCH] Move A - (A & B) -> ~B & A

On Fri, 17 Jul 2015, Marek Polacek wrote:


On Fri, Jul 17, 2015 at 02:23:50PM +0200, Richard Biener wrote:

+/* Fold A - (A & B) into ~B & A.  */
+(simplify
+ (minus (convert? @0) (convert? (bit_and:c @0 @1)))


I think you want :s on the bit_and and its convert?


Ok, I keep forgetting about this :(.


Are you sure you don't need to check for a nop conversion here?


I thought I didn't need it here, and couldn't find a testcase which
would break without tree_nop_conversion_p checks, but that doesn't mean
much.  So for extra safety I put the checks there.
I believe you were right that we don't need the checks, it should also be valid for narrowing / extending conversions.
Note that the equivalent "(X & Y) ^ Y as ~X & Y" does not have the optional converts. 


Bootstrapped/regtested on x86_64-linux, ok for trunk?

2015-07-17  Marek Polacek  <polacek@redhat.com>

	* fold-const.c (fold_binary_loc): Move A - (A & B) into ~B & A ...
	* match.pd: ... here.

	* gcc.dg/fold-minus-7.c: New test.

diff --git gcc/fold-const.c gcc/fold-const.c
index 93dd29d..fa321f4 100644
--- gcc/fold-const.c
+++ gcc/fold-const.c
@@ -9777,30 +9777,6 @@ fold_binary_loc (location_t loc,

      if (! FLOAT_TYPE_P (type))
	{
-	  /* Fold A - (A & B) into ~B & A.  */
-	  if (!TREE_SIDE_EFFECTS (arg0)
-	      && TREE_CODE (arg1) == BIT_AND_EXPR)
-	    {
-	      if (operand_equal_p (arg0, TREE_OPERAND (arg1, 1), 0))
-		{
-		  tree arg10 = fold_convert_loc (loc, type,
-						 TREE_OPERAND (arg1, 0));
-		  return fold_build2_loc (loc, BIT_AND_EXPR, type,
-				      fold_build1_loc (loc, BIT_NOT_EXPR,
-						   type, arg10),
-				      fold_convert_loc (loc, type, arg0));
-		}
-	      if (operand_equal_p (arg0, TREE_OPERAND (arg1, 0), 0))
-		{
-		  tree arg11 = fold_convert_loc (loc,
-						 type, TREE_OPERAND (arg1, 1));
-		  return fold_build2_loc (loc, BIT_AND_EXPR, type,
-				      fold_build1_loc (loc, BIT_NOT_EXPR,
-						   type, arg11),
-				      fold_convert_loc (loc, type, arg0));
-		}
-	    }
-
	  /* Fold (A & ~B) - (A & B) into (A ^ B) - B, where B is
	     any power of 2 minus 1.  */
	  if (TREE_CODE (arg0) == BIT_AND_EXPR
diff --git gcc/match.pd gcc/match.pd
index c335ada..700a692 100644
--- gcc/match.pd
+++ gcc/match.pd
@@ -662,6 +662,12 @@ along with GCC; see the file COPYING3.  If not see
 (bit_ior:c (bit_and:cs @0 (bit_not @2)) (bit_and:cs @1 @2))
 (bit_xor (bit_and (bit_xor @0 @1) @2) @0))

+/* Fold A - (A & B) into ~B & A.  */
+(simplify
+ (minus (convert? @0) (convert?:s (bit_and:cs @0 @1)))
+ (if (tree_nop_conversion_p (type, TREE_TYPE (@0))
+      && tree_nop_conversion_p (type, TREE_TYPE (@1)))
+  (convert (bit_and (bit_not @1) @0))))

/* Associate (p +p off1) +p off2 as (p +p (off1 + off2)).  */
(simplify
diff --git gcc/testsuite/gcc.dg/fold-minus-7.c gcc/testsuite/gcc.dg/fold-minus-7.c
index e69de29..7a49faa 100644
--- gcc/testsuite/gcc.dg/fold-minus-7.c
+++ gcc/testsuite/gcc.dg/fold-minus-7.c
@@ -0,0 +1,36 @@
+/* { dg-do compile } */
+/* { dg-options "-O -fdump-tree-cddce1" } */
+
+int
+f1 (int a, int b)
+{
+  int tem = a & b;
+  return a - tem;
+}
+
+int
+f2 (int a, int b)
+{
+  int tem = b & a;
+  return a - tem;
+}
+
+int
+f3 (unsigned int a, int b)
+{
+  return a - (a & b);
+}
+
+int
+f4 (int a, unsigned int b)
+{
+  return a - (a & b);
+}
+
+int
+f5 (int a, int b)
+{
+  return a - (unsigned) (b & a);
+}
+
+/* { dg-final { scan-tree-dump-not " - " "cddce1" } } */

	Marek



--
Marc Glisse
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