[4.9] GCC 4.9.0 official release refresh

Change-Id: Ic99a7da8b44b789a48aeec93b33e93944d6e6767

1 files changed, 15 insertions, 1 deletions

diff --git a/gcc-4.9/gcc/tree-vect-stmts.c b/gcc-4.9/gcc/tree-vect-stmts.c
index 884e769c8..1a51d6d7b 100644
--- a/gcc-4.9/gcc/tree-vect-stmts.c
+++ b/gcc-4.9/gcc/tree-vect-stmts.c
@@ -7848,7 +7848,21 @@ supportable_widening_operation (enum tree_code code, gimple stmt,
 					     stmt, vectype_out, vectype_in,
 					     code1, code2, multi_step_cvt,
 					     interm_types))
-	return true;
+        {
+          /* Elements in a vector with vect_used_by_reduction property cannot
+             be reordered if the use chain with this property does not have the
+             same operation.  One such an example is s += a * b, where elements
+             in a and b cannot be reordered.  Here we check if the vector defined
+             by STMT is only directly used in the reduction statement.  */
+          tree lhs = gimple_assign_lhs (stmt);
+          use_operand_p dummy;
+          gimple use_stmt;
+          stmt_vec_info use_stmt_info = NULL;
+          if (single_imm_use (lhs, &dummy, &use_stmt)
+              && (use_stmt_info = vinfo_for_stmt (use_stmt))
+              && STMT_VINFO_DEF_TYPE (use_stmt_info) == vect_reduction_def)
+            return true;
+        }
       c1 = VEC_WIDEN_MULT_LO_EXPR;
       c2 = VEC_WIDEN_MULT_HI_EXPR;
       break;