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

[Richard Guenther <richard.guenther@gmail.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" } } */
>