[PATCH 2/4] match.pd: Add x & ~(x & y) -> x & ~y pattern

[Rasmus Villemoes <rv at rasmusvillemoes dot dk>]

gcc.dg/20150120-2.c: New test

Clearing a certain subset of bits, for example to round down x to a
multiple of a power of 2, is sometimes written x & ~(x & y), where y
may or may not be a constant. It is shorter to use x & ~y,
particularly when y is a constant. gcc already does this when it is
spelled x - (x & y) or x ^ (x & y).

Signed-off-by: Rasmus Villemoes <rv@rasmusvillemoes.dk>
---
 gcc/match.pd                      |  6 ++++++
 gcc/testsuite/gcc.dg/20150120-2.c | 32 ++++++++++++++++++++++++++++++++
 2 files changed, 38 insertions(+)
 create mode 100644 gcc/testsuite/gcc.dg/20150120-2.c

diff --git gcc/match.pd gcc/match.pd
index ecefcfb..d25fc3a 100644
--- gcc/match.pd
+++ gcc/match.pd
@@ -261,6 +261,12 @@ along with GCC; see the file COPYING3.  If not see
  (if (TREE_CODE (@2) != SSA_NAME || has_single_use (@2))
   (bit_and (plus @0 @1) (bit_not @1))))
 
+/* x & ~(x & y) -> x & ~y */
+(simplify
+ (bit_and:c @0 (bit_not (bit_and:c@2 @0 @1)))
+ (if (TREE_CODE (@2) != SSA_NAME || has_single_use (@2))
+  (bit_and @0 (bit_not @1))))
+
 (simplify
  (abs (negate @0))
  (abs @0))
diff --git gcc/testsuite/gcc.dg/20150120-2.c gcc/testsuite/gcc.dg/20150120-2.c
new file mode 100644
index 0000000..976b654
--- /dev/null
+++ gcc/testsuite/gcc.dg/20150120-2.c
@@ -0,0 +1,32 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-original" } */
+
+/* x & ~(x & y) -> x & ~y */
+int fn1 (int x, int y)
+{
+	return x & ~(x & y);
+}
+int fn2 (int x, int y)
+{
+	return ~(x & y) & x;
+}
+int fn3 (int x, int y)
+{
+	return x & ~(y & x);
+}
+int fn4 (int x, int y)
+{
+	return ~(y & x) & x;
+}
+int fn5 (int z)
+{
+	return z & ~(z & 3);
+}
+int fn6 (int z)
+{
+	return ~(z & 3) & z;
+}
+
+
+/* { dg-final { scan-tree-dump-times "~y & x" 4 "original" } } */
+/* { dg-final { scan-tree-dump-times "z & -4" 2 "original" } } */
-- 
2.1.3