On Wed, 14 Feb 2024, Tamar Christina wrote:
> Hi All,
>
> Attaching a pragma to a loop which has a complex condition often gets the
> pragma
> dropped. e.g.
>
> #pragma GCC novector
> while (i < N && parse_tables_n--)
>
> before lowering this is represented as:
>
> if (ANNOTATE_EXPR <i <= 305 && parse_tables_n-- != 0, no-vector>) ...
>
> But after lowering the condition is broken appart and attached to the final
> component of the expression:
>
> if (parse_tables_n.2_2 != 0) goto <D.4456>; else goto <D.4453>;
> <D.4456>:
> iftmp.1D.4452 = 1;
> goto <D.4454>;
> <D.4453>:
> iftmp.1D.4452 = 0;
> <D.4454>:
> D.4451 = .ANNOTATE (iftmp.1D.4452, 2, 0);
> if (D.4451 != 0) goto <D.4442>; else goto <D.4440>;
> <D.4440>:
>
> and it's never heard from again because during replace_loop_annotate we only
> inspect the loop header and latch for annotations.
>
> Since annotations were supposed to apply to the loop as a whole this fixes it
> by also checking the loop exit src blocks for annotations.
>
> Bootstrapped Regtested on aarch64-none-linux-gnu and no issues.
>
> Ok for master?
I think this isn't entirely good. For simple cases for
do {} while the condition ends up in the latch while for while () {}
loops it ends up in the header. In your case the latch isn't empty
so it doesn't end up with the conditional.
I think your patch is OK to the point of looking at all loop exit
sources but you should elide the special-casing of header and
latch since it's really only exit conditionals that matter.
Richard.
> Thanks,
> Tamar
>
> gcc/ChangeLog:
>
> * tree-cfg.cc (replace_loop_annotate): Inspect loop edges for
> annotations.
>
> gcc/testsuite/ChangeLog:
>
> * gcc.dg/vect/vect-novect_gcond.c: New test.
>
> --- inline copy of patch --
> diff --git a/gcc/testsuite/gcc.dg/vect/vect-novect_gcond.c
> b/gcc/testsuite/gcc.dg/vect/vect-novect_gcond.c
> new file mode 100644
> index
> 0000000000000000000000000000000000000000..01e69cbef9d51b234c08a400c78dc078d53252f1
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/vect/vect-novect_gcond.c
> @@ -0,0 +1,39 @@
> +/* { dg-add-options vect_early_break } */
> +/* { dg-require-effective-target vect_early_break_hw } */
> +/* { dg-require-effective-target vect_int } */
> +/* { dg-additional-options "-O3" } */
> +
> +/* { dg-final { scan-tree-dump-not "LOOP VECTORIZED" "vect" } } */
> +
> +#include "tree-vect.h"
> +
> +#define N 306
> +#define NEEDLE 136
> +
> +int table[N];
> +
> +__attribute__ ((noipa))
> +int foo (int i, unsigned short parse_tables_n)
> +{
> + parse_tables_n >>= 9;
> + parse_tables_n += 11;
> +#pragma GCC novector
> + while (i < N && parse_tables_n--)
> + table[i++] = 0;
> +
> + return table[NEEDLE];
> +}
> +
> +int main ()
> +{
> + check_vect ();
> +
> +#pragma GCC novector
> + for (int j = 0; j < N; j++)
> + table[j] = -1;
> +
> + if (foo (0, 0xFFFF) != 0)
> + __builtin_abort ();
> +
> + return 0;
> +}
> diff --git a/gcc/tree-cfg.cc b/gcc/tree-cfg.cc
> index
> cdd439fe7506e7bc33654ffa027b493f23d278ac..a29681bffb902d2d05e3f18764ab519aacb3c5bc
> 100644
> --- a/gcc/tree-cfg.cc
> +++ b/gcc/tree-cfg.cc
> @@ -327,6 +327,10 @@ replace_loop_annotate (void)
> if (loop->latch)
> replace_loop_annotate_in_block (loop->latch, loop);
>
> + /* Then also check all other exits. */
> + for (auto e : get_loop_exit_edges (loop))
> + replace_loop_annotate_in_block (e->src, loop);
> +
> /* Push the global flag_finite_loops state down to individual loops.
> */
> loop->finite_p = flag_finite_loops;
> }
>
>
>
>
>
--
Richard Biener <rguent...@suse.de>
SUSE Software Solutions Germany GmbH,
Frankenstrasse 146, 90461 Nuernberg, Germany;
GF: Ivo Totev, Andrew McDonald, Werner Knoblich; (HRB 36809, AG Nuernberg)
