Hi!
As mentioned in the PR, for boolean x we currently optimize
in phiopt x ? 0 : -1 into -(int)!x but it can be optimized as
(int) x - 1 which is one less operation both in GIMPLE and in x86 assembly.
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
And/or, shall we have a match.pd optimization to turn that -(type)!x
for BOOLEAN_TYPE (or other 1 bit unsigned precision values) into
(type) - 1.
2020-12-05 Jakub Jelinek <ja...@redhat.com>
PR tree-optimization/96232
* tree-ssa-phiopt.c (conditional_replacement): Optimize
x ? 0 : -1 as (int) x - 1 rather than -(int)!x.
* gcc.dg/tree-ssa/pr96232-1.c: New test.
--- gcc/tree-ssa-phiopt.c.jj 2020-11-04 11:58:58.670252748 +0100
+++ gcc/tree-ssa-phiopt.c 2020-12-04 17:27:53.472837921 +0100
@@ -827,10 +827,24 @@ conditional_replacement (basic_block con
if (neg)
{
- cond = fold_convert_loc (gimple_location (stmt),
- TREE_TYPE (result), cond);
- cond = fold_build1_loc (gimple_location (stmt),
- NEGATE_EXPR, TREE_TYPE (cond), cond);
+ if (TREE_CODE (cond) == TRUTH_NOT_EXPR
+ && INTEGRAL_TYPE_P (TREE_TYPE (nonzero_arg)))
+ {
+ /* x ? 0 : -1 is better optimized as (int) x - 1 than
+ -(int)!x. */
+ cond = fold_convert_loc (gimple_location (stmt),
+ TREE_TYPE (result),
+ TREE_OPERAND (cond, 0));
+ cond = fold_build2_loc (gimple_location (stmt), PLUS_EXPR,
+ TREE_TYPE (result), cond, nonzero_arg);
+ }
+ else
+ {
+ cond = fold_convert_loc (gimple_location (stmt),
+ TREE_TYPE (result), cond);
+ cond = fold_build1_loc (gimple_location (stmt),
+ NEGATE_EXPR, TREE_TYPE (cond), cond);
+ }
}
else if (shift)
{
--- gcc/testsuite/gcc.dg/tree-ssa/pr96232-1.c.jj 2020-12-04
17:32:40.607615276 +0100
+++ gcc/testsuite/gcc.dg/tree-ssa/pr96232-1.c 2020-12-04 17:33:09.914286354
+0100
@@ -0,0 +1,11 @@
+/* PR tree-optimization/96232 */
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-optimized" } */
+/* { dg-final { scan-tree-dump " \\+ -1;" "optimized" } } */
+/* { dg-final { scan-tree-dump-not "~x_\[0-9]*\\\(D\\\)" "optimized" } } */
+
+int
+foo (_Bool x)
+{
+ return x ? 0 : -1;
+}
Jakub
