Hi Richard,
On 3 May 2017 at 10:19, Richard Biener <rguent...@suse.de> wrote:
>
> The following extends the very simplistic cost modeling I added somewhen
> late in the release process to, for all unknown misaligned refs, also
> apply this model for loops containing stores.
>
> The model basically says it's useless to peel for alignment if there's
> only a single DR that is affected or if, in case we'll end up using
> hw-supported misaligned loads, the cost of misaligned loads is the same
> as of aligned ones. Previously we'd usually align one of the stores
> with the theory that this improves (precious) store-bandwith.
>
> Note this is only a so slightly conservative (aka less peeling). We'll
> still apply peeling for alignment if you make the testcase use +=
> because then we'll align both the load and the store from v1.
>
> Bootstrap / regtest running on x86_64-unknown-linux-gnu.
>
> Richard.
>
> 2017-05-03 Richard Biener <rguent...@suse.de>
>
> * tree-vect-data-refs.c (vect_enhance_data_refs_alignment):
> When all DRs have unknown misaligned do not always peel
> when there is a store but apply the same costing model as if
> there were only loads.
>
> * gcc.dg/vect/costmodel/x86_64/costmodel-alignpeel.c: New testcase.
>
This patch (r247544) caused regressions on aarch64 and arm:
- PASS now FAIL [PASS => FAIL]:
Executed from: gcc.dg/vect/vect.exp
gcc.dg/vect/vect-44.c -flto -ffat-lto-objects
scan-tree-dump-times vect "Alignment of access forced using peeling" 1
gcc.dg/vect/vect-44.c -flto -ffat-lto-objects
scan-tree-dump-times vect "Vectorizing an unaligned access" 2
gcc.dg/vect/vect-44.c scan-tree-dump-times vect "Alignment of
access forced using peeling" 1
gcc.dg/vect/vect-44.c scan-tree-dump-times vect "Vectorizing an
unaligned access" 2
gcc.dg/vect/vect-50.c -flto -ffat-lto-objects
scan-tree-dump-times vect "Alignment of access forced using peeling" 1
gcc.dg/vect/vect-50.c -flto -ffat-lto-objects
scan-tree-dump-times vect "Vectorizing an unaligned access" 2
gcc.dg/vect/vect-50.c scan-tree-dump-times vect "Alignment of
access forced using peeling" 1
gcc.dg/vect/vect-50.c scan-tree-dump-times vect "Vectorizing an
unaligned access" 2
Thanks,
Christophe
> Index: gcc/tree-vect-data-refs.c
> ===================================================================
> --- gcc/tree-vect-data-refs.c (revision 247498)
> +++ gcc/tree-vect-data-refs.c (working copy)
> @@ -1715,18 +1741,18 @@ vect_enhance_data_refs_alignment (loop_v
> dr0 = first_store;
> }
>
> - /* In case there are only loads with different unknown misalignments,
> use
> - peeling only if it may help to align other accesses in the loop or
> + /* Use peeling only if it may help to align other accesses in the loop
> or
> if it may help improving load bandwith when we'd end up using
> unaligned loads. */
> tree dr0_vt = STMT_VINFO_VECTYPE (vinfo_for_stmt (DR_STMT (dr0)));
> - if (!first_store
> - && !STMT_VINFO_SAME_ALIGN_REFS (
> - vinfo_for_stmt (DR_STMT (dr0))).length ()
> + if (STMT_VINFO_SAME_ALIGN_REFS
> + (vinfo_for_stmt (DR_STMT (dr0))).length () == 0
> && (vect_supportable_dr_alignment (dr0, false)
> != dr_unaligned_supported
> - || (builtin_vectorization_cost (vector_load, dr0_vt, 0)
> - == builtin_vectorization_cost (unaligned_load, dr0_vt,
> -1))))
> + || (DR_IS_READ (dr0)
> + && (builtin_vectorization_cost (vector_load, dr0_vt, 0)
> + == builtin_vectorization_cost (unaligned_load,
> + dr0_vt, -1)))))
> do_peeling = false;
> }
>
>
> Index: gcc/testsuite/gcc.dg/vect/costmodel/x86_64/costmodel-alignpeel.c
> ===================================================================
> --- gcc/testsuite/gcc.dg/vect/costmodel/x86_64/costmodel-alignpeel.c
> (nonexistent)
> +++ gcc/testsuite/gcc.dg/vect/costmodel/x86_64/costmodel-alignpeel.c
> (working copy)
> @@ -0,0 +1,9 @@
> +/* { dg-do compile } */
> +
> +void func(double * __restrict__ v1, double * v2, unsigned n)
> +{
> + for (unsigned i = 0; i < n; ++i)
> + v1[i] = v2[i];
> +}
> +
> +/* { dg-final { scan-tree-dump-not "Alignment of access forced using
> peeling" "vect" } } */
