On Thu, 2 Sep 2021, Jakub Jelinek wrote:
> Hi!
>
> The overflow builtins work on infinite precision integers and then convert
> to the result type's precision, so any argument promotions are useless.
> The expand_arith_overflow expansion is able to demote the arguments itself
> through get_range_pos_neg and get_min_precision calls and if needed promote
> to whatever mode it decides to perform the operations in, but if there are
> any promotions it demoted, those are already expanded. Normally combine
> would remove the useless sign or zero extensions when it sees the result
> of those is only used in a lowpart subreg, but typically those lowpart
> subregs appear multiple times in the pattern so that they describe properly
> the overflow behavior and combine gives up, so we end up with e.g.
> movswl %si, %esi
> movswl %di, %edi
> imulw %si, %di
> seto %al
> where both movswl insns are useless.
>
> The following patch fixes it by demoting operands of the ifns (only gets
> rid of integral to integral conversions that increase precision).
> While IFN_{ADD,MUL}_OVERFLOW are commutative and just one simplify would be
> enough, IFN_SUB_OVERFLOW is not, therefore two simplifications.
>
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
It appears we're careful to accept different typed operands on
those IFNs at least in the few places I found, thus OK.
Thanks,
Richard.
> 2021-09-02 Jakub Jelinek <ja...@redhat.com>
>
> PR tree-optimization/99591
> * match.pd: Demote operands of IFN_{ADD,SUB,MUL}_OVERFLOW if they
> were promoted.
>
> * gcc.target/i386/pr99591.c: New test.
> * gcc.target/i386/pr97950.c: Match or reject setb or jn?b instructions
> together with seta or jn?a.
>
> --- gcc/match.pd.jj 2021-08-30 08:36:11.226516509 +0200
> +++ gcc/match.pd 2021-09-01 10:43:15.072908430 +0200
> @@ -5587,6 +5587,21 @@ (define_operator_list COND_TERNARY
> (with { tree t = TREE_TYPE (@0), cpx = build_complex_type (t); }
> (cmp (imagpart (IFN_MUL_OVERFLOW:cpx @0 @1)) { build_zero_cst (t); })))))
>
> +/* Demote operands of IFN_{ADD,SUB,MUL}_OVERFLOW. */
> +(for ovf (IFN_ADD_OVERFLOW IFN_SUB_OVERFLOW IFN_MUL_OVERFLOW)
> + (simplify
> + (ovf (convert@2 @0) @1)
> + (if (INTEGRAL_TYPE_P (TREE_TYPE (@0))
> + && INTEGRAL_TYPE_P (TREE_TYPE (@2))
> + && TYPE_PRECISION (TREE_TYPE (@2)) > TYPE_PRECISION (TREE_TYPE (@0)))
> + (ovf @0 @1)))
> + (simplify
> + (ovf @1 (convert@2 @0))
> + (if (INTEGRAL_TYPE_P (TREE_TYPE (@0))
> + && INTEGRAL_TYPE_P (TREE_TYPE (@2))
> + && TYPE_PRECISION (TREE_TYPE (@2)) > TYPE_PRECISION (TREE_TYPE (@0)))
> + (ovf @1 @0))))
> +
> /* Simplification of math builtins. These rules must all be optimizations
> as well as IL simplifications. If there is a possibility that the new
> form could be a pessimization, the rule should go in the canonicalization
> --- gcc/testsuite/gcc.target/i386/pr99591.c.jj 2021-09-01
> 10:49:32.286556087 +0200
> +++ gcc/testsuite/gcc.target/i386/pr99591.c 2021-09-01 10:49:17.450766597
> +0200
> @@ -0,0 +1,32 @@
> +/* PR tree-optimization/99591 */
> +/* { dg-do compile } */
> +/* { dg-options "-O2" } */
> +/* { dg-final { scan-assembler-not "\tmovs\[bw]l\t" } } */
> +
> +int
> +foo (signed char a, signed char b)
> +{
> + signed char r;
> + return __builtin_add_overflow (a, b, &r);
> +}
> +
> +int
> +bar (short a, short b)
> +{
> + short r;
> + return __builtin_add_overflow (a, b, &r);
> +}
> +
> +int
> +baz (signed char a, signed char b)
> +{
> + signed char r;
> + return __builtin_add_overflow ((int) a, (int) b, &r);
> +}
> +
> +int
> +qux (short a, short b)
> +{
> + short r;
> + return __builtin_add_overflow ((int) a, (int) b, &r);
> +}
> --- gcc/testsuite/gcc.target/i386/pr97950.c.jj 2020-11-24
> 23:16:27.601004905 +0100
> +++ gcc/testsuite/gcc.target/i386/pr97950.c 2021-09-02 09:28:06.934382216
> +0200
> @@ -1,10 +1,10 @@
> /* PR target/95950 */
> /* { dg-do compile } */
> /* { dg-options "-O2 -mtune=generic" } */
> -/* { dg-final { scan-assembler-times "\tseta\t" 4 } } */
> +/* { dg-final { scan-assembler-times "\tset\[ab]\t" 4 } } */
> /* { dg-final { scan-assembler-times "\tseto\t" 16 } } */
> /* { dg-final { scan-assembler-times "\tsetc\t" 4 } } */
> -/* { dg-final { scan-assembler-not "\tjn?a\t" } } */
> +/* { dg-final { scan-assembler-not "\tjn?\[ab]\t" } } */
> /* { dg-final { scan-assembler-not "\tjn?o\t" } } */
> /* { dg-final { scan-assembler-not "\tjn?c\t" } } */
>
>
> Jakub
>
>
--
Richard Biener <rguent...@suse.de>
SUSE Software Solutions Germany GmbH, Maxfeldstrasse 5, 90409 Nuernberg,
Germany; GF: Felix Imendörffer; HRB 36809 (AG Nuernberg)
