match.pd: reassociate multiplications

	* match.pd ((X * CST) * Y): Reassociate to (X * Y) * CST.
testsuite/
	* gcc.dg/tree-ssa/assoc-2.c: New testcase.

From-SVN: r250523

gcc/ChangeLog

-2017-07-07  Torsten Duwe  <duwe@suse.de>
+2017-07-25  Alexander Monakov  <amonakov@ispras.ru>
+
+	* match.pd ((X * CST) * Y): Reassociate to (X * Y) * CST.
+
+2017-07-25  Torsten Duwe  <duwe@suse.de>
 
 	* common.opt: Introduce -fpatchable-function-entry
 	command line option, and its variables function_entry_patch_area_size

gcc/match.pd

@@ -2213,6 +2213,14 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
  (mult @0 integer_minus_onep)
  (negate @0))
 
+/* Reassociate (X * CST) * Y to (X * Y) * CST.  This does not introduce
+   signed overflow for CST != 0 && CST != -1.  */
+(simplify
+ (mult:c (mult:s @0 INTEGER_CST@1) @2)
+ (if (TREE_CODE (@2) != INTEGER_CST
+      && !integer_zerop (@1) && !integer_minus_onep (@1))
+  (mult (mult @0 @2) @1)))
+
 /* True if we can easily extract the real and imaginary parts of a complex
    number.  */
 (match compositional_complex

gcc/testsuite/ChangeLog

-2017-07-07  Torsten Duwe  <duwe@suse.de>
+2017-07-25  Alexander Monakov  <amonakov@ispras.ru>
+
+	* gcc.dg/tree-ssa/assoc-2.c: New testcase.
+
+2017-07-25  Torsten Duwe  <duwe@suse.de>
 
 	* c-c++-common/patchable_function_entry-default.c: New test.
 	* c-c++-common/patchable_function_entry-decl.c: Likewise.

gcc/testsuite/gcc.dg/tree-ssa/assoc-2.c

+/* { dg-do compile } */
+/* { dg-options "-O -fdump-tree-gimple-raw -fdump-tree-optimized-raw" } */
+
+int f0(int a, int b){
+  return a * 33 * b * 55;
+}
+
+/* { dg-final { scan-tree-dump-times "mult_expr" 2 "gimple" } } */