On Wed, Aug 22, 2018 at 11:31 AM Richard Sandiford
<richard.sandif...@arm.com> wrote:
>
> This patch is the first part of the fix for PR 86725. We would
> treat x_1 in:
>
> outer1:
> x_1 = PHI <x_4(outer2), ...>;
> ...
>
> inner:
> x_2 = ...x_1...;
> ...
> x_3 = ...;
> ...
>
> outer2:
> x_4 = PHI <x_3(inner)>;
> ...
>
> as a double reduction without checking what kind of statement x_2 is.
> In practice it has to be a phi, since for other x_2, x_1 would simply
> be a loop invariant that gets used for every inner loop iteration.
>
> The idea with doing this patch first is that, by checking x_2 really
> is a phi, we can hand off the validation of the rest of the reduction
> to the phi analysis in the inner loop.
>
> The test case is a variant of the one in the PR.
>
> Tested on aarch64-linux-gnu (with and without SVE), aarch64_be-elf
> and x86_64-linux-gnu. OK for trunk and GCC 8?
OK.
Thanks,
Richard.
> Richard
>
>
> 2018-08-22 Richard Sandiford <richard.sandif...@arm.com>
>
> gcc/
> PR tree-optimization/86725
> * tree-vect-loop.c (vect_is_simple_reduction): When treating
> an outer loop phi as a double reduction, make sure that the
> single user of the phi result is an inner loop phi.
>
> gcc/testsuite/
> PR tree-optimization/86725
> * gcc.dg/vect/no-scevccp-pr86725-1.c: New test.
>
> Index: gcc/tree-vect-loop.c
> ===================================================================
> --- gcc/tree-vect-loop.c 2018-08-21 14:47:07.047174151 +0100
> +++ gcc/tree-vect-loop.c 2018-08-22 10:25:06.682099699 +0100
> @@ -2992,6 +2992,7 @@ vect_is_simple_reduction (loop_vec_info
> && loop->inner
> && flow_bb_inside_loop_p (loop->inner, gimple_bb (def1))
> && is_gimple_assign (def1)
> + && is_a <gphi *> (phi_use_stmt)
> && flow_bb_inside_loop_p (loop->inner, gimple_bb (phi_use_stmt)))
> {
> if (dump_enabled_p ())
> Index: gcc/testsuite/gcc.dg/vect/no-scevccp-pr86725-1.c
> ===================================================================
> --- /dev/null 2018-07-26 10:26:13.137955424 +0100
> +++ gcc/testsuite/gcc.dg/vect/no-scevccp-pr86725-1.c 2018-08-22
> 10:25:06.682099699 +0100
> @@ -0,0 +1,26 @@
> +/* { dg-do compile } */
> +/* { dg-additional-options "-O -w" } */
> +
> +int foo;
> +int
> +nr (int xe, int z)
> +{
> + int oo, wo = 0;
> +
> + for (oo = 0; oo < 4; ++oo)
> + {
> + int qq;
> +
> + int old_wo = wo;
> + for (qq = 0; qq < 2; ++qq)
> + {
> + wo = z + qq + old_wo;
> + xe += wo;
> + }
> + }
> + foo = wo;
> + return xe;
> +}
> +
> +/* { dg-final { scan-tree-dump-not "double reduction: wo" "vect" } } */
> +/* { dg-final { scan-tree-dump-not "OUTER LOOP VECTORIZED" "vect" } } */
