re PR tree-optimization/64910 (tree reassociation results in poor code)

	PR tree-optimization/64910
	* tree-ssa-reassoc.c (reassociate_bb): Restrict last change to
	cases where we have 3 or more operands.

From-SVN: r251751

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 5363790..1b3bddb 100644 (file)
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,9 @@
+2017-09-05  Jeff Law  <law@redhat.com>
+
+       PR tree-optimization/64910
+       * tree-ssa-reassoc.c (reassociate_bb): Restrict last change to
+       cases where we have 3 or more operands.
+
 2017-09-05  Jakub Jelinek  <jakub@redhat.com>
 
        PR middle-end/81768

diff --git a/gcc/tree-ssa-reassoc.c b/gcc/tree-ssa-reassoc.c
index 7604819..2fb6aef 100644 (file)
--- a/gcc/tree-ssa-reassoc.c
+++ b/gcc/tree-ssa-reassoc.c
@@ -5763,14 +5763,15 @@ reassociate_bb (basic_block bb)
                             "Width = %d was chosen for reassociation\n", width);
 
 
-                 /* For binary bit operations, if the last operand in
-                    OPS is a constant, move it to the front.  This
-                    helps ensure that we generate (X & Y) & C rather
-                    than (X & C) & Y.  The former will often match
-                    a canonical bit test when we get to RTL.  */
-                 if ((rhs_code == BIT_AND_EXPR
-                      || rhs_code == BIT_IOR_EXPR
-                      || rhs_code == BIT_XOR_EXPR)
+                 /* For binary bit operations, if there are at least 3
+                    operands and the last last operand in OPS is a constant,
+                    move it to the front.  This helps ensure that we generate
+                    (X & Y) & C rather than (X & C) & Y.  The former will
+                    often match a canonical bit test when we get to RTL.  */
+                 if (ops.length () != 2
+                     && (rhs_code == BIT_AND_EXPR
+                         || rhs_code == BIT_IOR_EXPR
+                         || rhs_code == BIT_XOR_EXPR)
                      && TREE_CODE (ops.last ()->op) == INTEGER_CST)
                    std::swap (*ops[0], *ops[ops_num - 1]);