PR53979: add transform (a ^ b) | a -> a | b

[Prathamesh Kulkarni]

Hi Richard,
The attached patch adds the transform (a ^ b) | a -> a | b suggested in PR53979.
Bootstrap+tested on x86_64-unknown-linux-gnu.
OK to commit ?

Thanks,
Prathamesh

2016-10-20  Prathamesh Kulkarni  <prathamesh.kulka...@linaro.org>

        PR tree-optimization/53979
        * match.pd ((a ^ b) | a -> a | b): New pattern.

testsuite/
        * gcc.dg/pr53979-1.c: New test-case.
        * gcc.dg/pr53979-2.c: Likewise.

diff --git a/gcc/match.pd b/gcc/match.pd
index b782a1e..7888459 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -541,6 +541,12 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
  (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)))
+
+/* PR53979: Transform ((a ^ b) | a) -> (a | b) */
+(simplify
+  (bit_ior:c (bit_xor:c @0 @1) @0)
+  (bit_ior @0 @1))
+
 /* Simplify (~X & Y) to X ^ Y if we know that (X & ~Y) is 0.  */
 #if GIMPLE
 (simplify
diff --git a/gcc/testsuite/gcc.dg/pr53979-1.c b/gcc/testsuite/gcc.dg/pr53979-1.c
new file mode 100644
index 0000000..aee54f5
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr53979-1.c
@@ -0,0 +1,9 @@
+/* { dg-do compile } */
+/* { dg-options "-fdump-tree-gimple" } */
+
+unsigned f1(unsigned a, unsigned b)
+{
+  return (a ^ b) | a; 
+}
+
+/* { dg-final { scan-tree-dump "a | b" "gimple" } } */
diff --git a/gcc/testsuite/gcc.dg/pr53979-2.c b/gcc/testsuite/gcc.dg/pr53979-2.c
new file mode 100644
index 0000000..be2607a
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr53979-2.c
@@ -0,0 +1,11 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-forwprop-details" } */
+
+unsigned f(unsigned a, unsigned b)
+{
+  unsigned t1 = a ^ b;
+  unsigned t2 = t1 | a;
+  return t2;
+}
+
+/* { dg-final { scan-tree-dump "gimple_simplified to t2_\[0-9\] = 
a_\[0-9\]*\\(D\\) | b_\[0-9\]*\\(D\\)" "forwprop1" } } */