Re: [patch tree-optimization]: allow branch-cost optimization for truth-and/or on mode-expanded simple boolean-operands

[Richard Guenther <richard dot guenther at gmail dot com>]

On Thu, Oct 20, 2011 at 3:08 PM, Kai Tietz <ktietz@redhat.com> wrote:
> Hello,
>
> this patch re-enables the branch-cost optimization on simple boolean-typed operands, which are casted to a wider integral type. ?This happens due casts from
> boolean-types are preserved, but FE might expands simple-expression to wider mode.
>
> I added two tests for already working branch-cost optimization for IA-architecture and
> two for explicit checking for boolean-type.
>
> ChangeLog
>
> 2011-10-20 ?Kai Tietz ?<ktietz@redhat.com>
>
> ? ? ? ?* fold-const.c (simple_operand_p_2): Handle integral
> ? ? ? ?casts from boolean-operands.
>
> 2011-10-20 ?Kai Tietz ?<ktietz@redhat.com>
>
> ? ? ? ?* gcc.target/i386/branch-cost1.c: New test.
> ? ? ? ?* gcc.target/i386/branch-cost2.c: New test.
> ? ? ? ?* gcc.target/i386/branch-cost3.c: New test.
> ? ? ? ?* gcc.target/i386/branch-cost4.c: New test.
>
> Bootstrapped and regression tested on x86_64-unknown-linux-gnu for all languages including Ada and Obj-C++. ?Ok for apply?
>
> Regards,
> Kai
>
> Index: gcc-head/gcc/testsuite/gcc.target/i386/branch-cost2.c
> ===================================================================
> --- /dev/null
> +++ gcc-head/gcc/testsuite/gcc.target/i386/branch-cost2.c
> @@ -0,0 +1,16 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -fdump-tree-gimple -mbranch-cost=2" } */
> +
> +extern int doo (void);
> +
> +int
> +foo (int a, int b)
> +{
> + ?if (a && b)
> + ? return doo ();
> + ?return 0;
> +}
> +
> +/* { dg-final { scan-tree-dump-times "if " 1 "gimple" } } */
> +/* { dg-final { scan-tree-dump-times " & " 1 "gimple" } } */
> +/* { dg-final { cleanup-tree-dump "gimple" } } */
> Index: gcc-head/gcc/testsuite/gcc.target/i386/branch-cost3.c
> ===================================================================
> --- /dev/null
> +++ gcc-head/gcc/testsuite/gcc.target/i386/branch-cost3.c
> @@ -0,0 +1,16 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -fdump-tree-gimple -mbranch-cost=2" } */
> +
> +extern int doo (void);
> +
> +int
> +foo (_Bool a, _Bool b)
> +{
> + ?if (a && b)
> + ? return doo ();
> + ?return 0;
> +}
> +
> +/* { dg-final { scan-tree-dump-times "if " 1 "gimple" } } */
> +/* { dg-final { scan-tree-dump-times " & " 1 "gimple" } } */
> +/* { dg-final { cleanup-tree-dump "gimple" } } */
> Index: gcc-head/gcc/testsuite/gcc.target/i386/branch-cost4.c
> ===================================================================
> --- /dev/null
> +++ gcc-head/gcc/testsuite/gcc.target/i386/branch-cost4.c
> @@ -0,0 +1,16 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -fdump-tree-gimple -mbranch-cost=0" } */
> +
> +extern int doo (void);
> +
> +int
> +foo (_Bool a, _Bool b)
> +{
> + ?if (a && b)
> + ? return doo ();
> + ?return 0;
> +}
> +
> +/* { dg-final { scan-tree-dump-times "if " 2 "gimple" } } */
> +/* { dg-final { scan-tree-dump-not " & " "gimple" } } */
> +/* { dg-final { cleanup-tree-dump "gimple" } } */
> Index: gcc-head/gcc/fold-const.c
> ===================================================================
> --- gcc-head.orig/gcc/fold-const.c
> +++ gcc-head/gcc/fold-const.c
> @@ -3706,6 +3706,19 @@ simple_operand_p_2 (tree exp)
> ? /* Strip any conversions that don't change the machine mode. ?*/
> ? STRIP_NOPS (exp);
>
> + ?/* Handle integral widening casts from boolean-typed
> + ? ? expressions as simple. ?This happens due casts from
> + ? ? boolean-types are preserved, but FE might expands
> + ? ? simple-expression to wider mode. ?*/
> + ?if (INTEGRAL_TYPE_P (TREE_TYPE (exp))
> + ? ? ?&& CONVERT_EXPR_P (exp)
> + ? ? ?&& TREE_CODE (TREE_TYPE (TREE_OPERAND (exp, 0)))
> + ? ? ? ?== BOOLEAN_TYPE)
> + ? ?{
> + ? ? ?exp = TREE_OPERAND (exp, 0);
> + ? ? ?STRIP_NOPS (exp);
> + ? ?}
> +

Huh, well.  I think the above is just too special and you instead should
replace the existing STRIP_NOPS by

while (CONVERT_EXPR_P (exp))
  exp = TREE_OPERAND (exp, 0);

with a comment that conversions are considered simple.

Ok with that change, if it bootstraps & tests ok.

Richard.

> ? code = TREE_CODE (exp);
>
> ? if (TREE_SIDE_EFFECTS (exp)
> Index: gcc-head/gcc/testsuite/gcc.target/i386/branch-cost1.c
> ===================================================================
> --- /dev/null
> +++ gcc-head/gcc/testsuite/gcc.target/i386/branch-cost1.c
> @@ -0,0 +1,16 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -fdump-tree-gimple -mbranch-cost=0" } */
> +
> +extern int doo (void);
> +
> +int
> +foo (int a, int b)
> +{
> + ?if (a && b)
> + ? return doo ();
> + ?return 0;
> +}
> +
> +/* { dg-final { scan-tree-dump-times "if " 2 "gimple" } } */
> +/* { dg-final { scan-tree-dump-not " & " "gimple" } } */
> +/* { dg-final { cleanup-tree-dump "gimple" } } */
>