match.pd: ~X & Y to X ^ Y in some cases

[Marc Glisse <marc dot glisse at inria dot fr>]

Hello,

maybe this would fit better in VRP, but it is easier (and not completely 
useless) to put it in match.pd.

Since the transformation is restricted to GIMPLE, I think I don't need to 
check that @0 is SSA_NAME. I didn't test if @0 has pointer type before 
calling get_range_info because we are doing bit_not on it, but it looks 
like I should because we can do bitops on pointers?

Adjustment for pr69270.c is exactly the same as in the previous patch from 
today :-)

Bootstrap+regtest on powerpc64le-unknown-linux-gnu.


2016-05-16  Marc Glisse  <marc.glisse@inria.fr>

gcc/
	* match.pd (~X & Y): New transformation.

gcc/testsuite/
	* gcc.dg/tree-ssa/pr69270.c: Adjust.
	* gcc.dg/tree-ssa/andnot-1.c: New testcase.


--
Marc Glisse

Index: gcc/match.pd
===================================================================
--- gcc/match.pd	(revision 236194)
+++ gcc/match.pd	(working copy)
@@ -496,20 +496,27 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
   (minus @1 (bit_xor @0 @1)))
 
 /* Simplify (X & ~Y) | (~X & Y) -> X ^ Y.  */
 (simplify
  (bit_ior (bit_and:c @0 (bit_not @1)) (bit_and:c (bit_not @0) @1))
   (bit_xor @0 @1))
 (simplify
  (bit_ior:c (bit_and @0 INTEGER_CST@2) (bit_and (bit_not @0) INTEGER_CST@1))
  (if (wi::bit_not (@2) == @1)
   (bit_xor @0 @1)))
+/* Simplify (~X & Y) to X ^ Y if we know that (X & ~Y) is 0.  */
+#if GIMPLE
+(simplify
+ (bit_and (bit_not @0) INTEGER_CST@1)
+ (if ((get_nonzero_bits (@0) & wi::bit_not (@1)) == 0)
+  (bit_xor @0 @1)))
+#endif
 
 /* X % Y is smaller than Y.  */
 (for cmp (lt ge)
  (simplify
   (cmp (trunc_mod @0 @1) @1)
   (if (TYPE_UNSIGNED (TREE_TYPE (@0)))
    { constant_boolean_node (cmp == LT_EXPR, type); })))
 (for cmp (gt le)
  (simplify
   (cmp @1 (trunc_mod @0 @1))
Index: gcc/testsuite/gcc.dg/tree-ssa/andnot-1.c
===================================================================
--- gcc/testsuite/gcc.dg/tree-ssa/andnot-1.c	(revision 0)
+++ gcc/testsuite/gcc.dg/tree-ssa/andnot-1.c	(working copy)
@@ -0,0 +1,12 @@
+/* { dg-do compile } */
+/* { dg-options "-O -fdump-tree-optimized-raw" } */
+
+unsigned f(unsigned i){
+  i >>= __SIZEOF_INT__ * __CHAR_BIT__ - 3;
+  i = ~i;
+  return i & 7;
+}
+
+/* { dg-final { scan-tree-dump "bit_xor_expr" "optimized" } } */
+/* { dg-final { scan-tree-dump-not "bit_not_expr" "optimized" } } */
+/* { dg-final { scan-tree-dump-not "bit_and_expr" "optimized" } } */
Index: gcc/testsuite/gcc.dg/tree-ssa/pr69270.c
===================================================================
--- gcc/testsuite/gcc.dg/tree-ssa/pr69270.c	(revision 236194)
+++ gcc/testsuite/gcc.dg/tree-ssa/pr69270.c	(working copy)
@@ -1,21 +1,19 @@
 /* { dg-do compile } */
 /* { dg-options "-O2 -fsplit-paths -fdump-tree-dom3-details" } */
 
 /* There should be two references to bufferstep that turn into
    constants.  */
 /* { dg-final { scan-tree-dump-times "Replaced .bufferstep_\[0-9\]+. with constant .0." 1 "dom3"} } */
 /* { dg-final { scan-tree-dump-times "Replaced .bufferstep_\[0-9\]+. with constant .1." 1 "dom3"} } */
 
 /* And some assignments ought to fold down to constants.  */
-/* { dg-final { scan-tree-dump-times "Folded to: _\[0-9\]+ = -1;" 1 "dom3"} } */
-/* { dg-final { scan-tree-dump-times "Folded to: _\[0-9\]+ = -2;" 1 "dom3"} } */
 /* { dg-final { scan-tree-dump-times "Folded to: _\[0-9\]+ = 1;" 1 "dom3"} } */
 /* { dg-final { scan-tree-dump-times "Folded to: _\[0-9\]+ = 0;" 1 "dom3"} } */
 
 /* The XOR operations should have been optimized to constants.  */
 /* { dg-final { scan-tree-dump-not "bit_xor" "dom3"} } */
 
 
 extern int *stepsizeTable;
 
 void