[PR25530] Convert (unsigned t / 2) * 2 into (unsigned t & ~1)

["Hurugalawadi, Naveen" <Naveen.Hurugalawadi@caviumnetworks.com>]

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Hi,

Please find attached the patch PR25530.patch that converts the pattern:-
(unsigned / 2) * 2 is into (unsigned & ~1).

Please review and let me know if its okay.

Regression tested on AARH64 and x86_64.

Thanks,
Naveen

gcc/testsuite/ChangeLog:

2015-07-07  Naveen H.S  <Naveen.Hurugalawadi@caviumnetworks.com>

	PR middle-end/25530
	* gcc.dg/pr25530.c: New test.

gcc/ChangeLog:

2015-07-07  Naveen H.S  <Naveen.Hurugalawadi@caviumnetworks.com>

	PR middle-end/25530
	* match.pd (mult (div @0 INTEGER_CST@1) INTEGER_CST@1) : 
	New simplifier.

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diff --git a/gcc/match.pd b/gcc/match.pd
index 53e911a..2c9e408 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -529,6 +529,17 @@ along with GCC; see the file COPYING3.  If not see
   (bitop (bit_and:c @0 @1) (bit_and @2 @1))
   (bit_and (bitop @0 @2) @1)))
 
+/* Simplify (unsigned t / 2) * 2 -> unsigned t & ~1.  */
+/* PR25530.  */
+(for div (trunc_div ceil_div floor_div round_div exact_div)
+ (simplify
+  (mult (div @0 INTEGER_CST@1) INTEGER_CST@1)
+  (with { tree n2 = build_int_cst (TREE_TYPE (@0),
+				   wi::exact_log2 (@1)); }
+  (if (TYPE_UNSIGNED (TREE_TYPE (@0)))
+   (bit_and @0 (lshift (rshift { build_minus_one_cst (TREE_TYPE (@0)); }
+			       { n2; }) { n2; }))))))
+
 /* (x | CST1) & CST2 -> (x & CST2) | (CST1 & CST2) */
 (simplify
   (bit_and (bit_ior @0 CONSTANT_CLASS_P@1) CONSTANT_CLASS_P@2)
diff --git a/gcc/testsuite/gcc.dg/pr25530.c b/gcc/testsuite/gcc.dg/pr25530.c
new file mode 100644
index 0000000..61e19cc
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr25530.c
@@ -0,0 +1,10 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-optimized" } */
+
+int
+f (unsigned t)
+{
+  return (t / 2) * 2;
+}
+
+/* { dg-final { scan-tree-dump "\& -2" "optimized" } } */