On Tue, May 1, 2018 at 8:34 PM, Richard Sandiford
<richard.sandif...@linaro.org> wrote:
> The problem in this PR was that we didn't consider aliases between
> writes in the same strided group. After tightening the early exit
> we get the expected abs(step) >= 2 versioning check.
>
> Tested on aarch64-linux-gnu and x86_64-linux-gnu. OK for trunk
> and GCC 8?
OK for trunk and branch.
Thanks,
Richard.
> Thanks,
> Richard
>
>
> 2018-05-01 Richard Sandiford <richard.sandif...@linaro.org>
>
> gcc/
> PR tree-optimization/85586
> * tree-vect-data-refs.c (vect_analyze_data_ref_dependence): Only
> exit early for statements in the same group if the accesses are
> not strided.
>
> gcc/testsuite/
> PR tree-optimization/85586
> * gcc.dg/vect/pr85586.c: New test.
>
> Index: gcc/tree-vect-data-refs.c
> ===================================================================
> --- gcc/tree-vect-data-refs.c 2018-05-01 19:30:22.344979421 +0100
> +++ gcc/tree-vect-data-refs.c 2018-05-01 19:32:10.404466158 +0100
> @@ -305,9 +305,11 @@ vect_analyze_data_ref_dependence (struct
> return false;
>
> /* We do not have to consider dependences between accesses that belong
> - to the same group. */
> + to the same group, unless the stride could be smaller than the
> + group size. */
> if (GROUP_FIRST_ELEMENT (stmtinfo_a)
> - && GROUP_FIRST_ELEMENT (stmtinfo_a) == GROUP_FIRST_ELEMENT
> (stmtinfo_b))
> + && GROUP_FIRST_ELEMENT (stmtinfo_a) == GROUP_FIRST_ELEMENT (stmtinfo_b)
> + && !STMT_VINFO_STRIDED_P (stmtinfo_a))
> return false;
>
> /* Even if we have an anti-dependence then, as the vectorized loop covers
> at
> Index: gcc/testsuite/gcc.dg/vect/pr85586.c
> ===================================================================
> --- /dev/null 2018-04-20 16:19:46.369131350 +0100
> +++ gcc/testsuite/gcc.dg/vect/pr85586.c 2018-05-01 19:32:10.403466206 +0100
> @@ -0,0 +1,43 @@
> +#define N 100
> +
> +void __attribute__ ((noipa))
> +foo (int *out, int *in, int step)
> +{
> + for (int i = 0; i < N; ++i)
> + {
> + out[0] = in[i];
> + out[1] = 2;
> + out += step;
> + }
> +}
> +
> +int in[N];
> +int out[N * 2];
> +
> +int
> +main (void)
> +{
> + for (int i = 0; i < N; ++i)
> + {
> + in[i] = i * (i + 1);
> + asm volatile ("" ::: "memory");
> + }
> +
> + foo (out, in, 1);
> + for (int i = 0; i < N; ++i)
> + if (out[i] != in[i])
> + __builtin_abort ();
> + if (out[N] != 2)
> + __builtin_abort ();
> +
> + foo (out + N - 1, in, -1);
> + if (out[0] != in[N - 1])
> + __builtin_abort ();
> + for (int i = 1; i <= N; ++i)
> + if (out[i] != 2)
> + __builtin_abort ();
> +
> + return 0;
> +}
> +
> +/* { dg-final { scan-tree-dump-times "LOOP VECTORIZED" 1 "vect" { target
> vect_int } } } */
