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Re: [PATCH] Fix PR78189
On 10 November 2016 at 09:34, Richard Biener <rguenther@suse.de> wrote:
> On Wed, 9 Nov 2016, Christophe Lyon wrote:
>
>> On 9 November 2016 at 09:36, Bin.Cheng <amker.cheng@gmail.com> wrote:
>> > On Tue, Nov 8, 2016 at 9:11 AM, Richard Biener <rguenther@suse.de> wrote:
>> >> On Mon, 7 Nov 2016, Christophe Lyon wrote:
>> >>
>> >>> Hi Richard,
>> >>>
>> >>>
>> >>> On 7 November 2016 at 09:01, Richard Biener <rguenther@suse.de> wrote:
>> >>> >
>> >>> > The following fixes an oversight when computing alignment in the
>> >>> > vectorizer.
>> >>> >
>> >>> > Bootstrapped and tested on x86_64-unknown-linux-gnu, applied to trunk.
>> >>> >
>> >>> > Richard.
>> >>> >
>> >>> > 2016-11-07 Richard Biener <rguenther@suse.de>
>> >>> >
>> >>> > PR tree-optimization/78189
>> >>> > * tree-vect-data-refs.c (vect_compute_data_ref_alignment): Fix
>> >>> > alignment computation.
>> >>> >
>> >>> > * g++.dg/torture/pr78189.C: New testcase.
>> >>> >
>> >>> > Index: gcc/testsuite/g++.dg/torture/pr78189.C
>> >>> > ===================================================================
>> >>> > --- gcc/testsuite/g++.dg/torture/pr78189.C (revision 0)
>> >>> > +++ gcc/testsuite/g++.dg/torture/pr78189.C (working copy)
>> >>> > @@ -0,0 +1,41 @@
>> >>> > +/* { dg-do run } */
>> >>> > +/* { dg-additional-options "-ftree-slp-vectorize -fno-vect-cost-model" } */
>> >>> > +
>> >>> > +#include <cstddef>
>> >>> > +
>> >>> > +struct A
>> >>> > +{
>> >>> > + void * a;
>> >>> > + void * b;
>> >>> > +};
>> >>> > +
>> >>> > +struct alignas(16) B
>> >>> > +{
>> >>> > + void * pad;
>> >>> > + void * misaligned;
>> >>> > + void * pad2;
>> >>> > +
>> >>> > + A a;
>> >>> > +
>> >>> > + void Null();
>> >>> > +};
>> >>> > +
>> >>> > +void B::Null()
>> >>> > +{
>> >>> > + a.a = nullptr;
>> >>> > + a.b = nullptr;
>> >>> > +}
>> >>> > +
>> >>> > +void __attribute__((noinline,noclone))
>> >>> > +NullB(void * misalignedPtr)
>> >>> > +{
>> >>> > + B* b = reinterpret_cast<B*>(reinterpret_cast<char *>(misalignedPtr) - offsetof(B, misaligned));
>> >>> > + b->Null();
>> >>> > +}
>> >>> > +
>> >>> > +int main()
>> >>> > +{
>> >>> > + B b;
>> >>> > + NullB(&b.misaligned);
>> >>> > + return 0;
>> >>> > +}
>> >>> > diff --git gcc/tree-vect-data-refs.c b/gcc/tree-vect-data-refs.c
>> >>> > index 9346cfe..b03cb1e 100644
>> >>> > --- gcc/tree-vect-data-refs.c
>> >>> > +++ gcc/tree-vect-data-refs.c
>> >>> > @@ -773,10 +773,25 @@ vect_compute_data_ref_alignment (struct data_reference *dr)
>> >>> > base = ref;
>> >>> > while (handled_component_p (base))
>> >>> > base = TREE_OPERAND (base, 0);
>> >>> > + unsigned int base_alignment;
>> >>> > + unsigned HOST_WIDE_INT base_bitpos;
>> >>> > + get_object_alignment_1 (base, &base_alignment, &base_bitpos);
>> >>> > + /* As data-ref analysis strips the MEM_REF down to its base operand
>> >>> > + to form DR_BASE_ADDRESS and adds the offset to DR_INIT we have to
>> >>> > + adjust things to make base_alignment valid as the alignment of
>> >>> > + DR_BASE_ADDRESS. */
>> >>> > if (TREE_CODE (base) == MEM_REF)
>> >>> > - base = build2 (MEM_REF, TREE_TYPE (base), base_addr,
>> >>> > - build_int_cst (TREE_TYPE (TREE_OPERAND (base, 1)), 0));
>> >>> > - unsigned int base_alignment = get_object_alignment (base);
>> >>> > + {
>> >>> > + base_bitpos -= mem_ref_offset (base).to_short_addr () * BITS_PER_UNIT;
>> >>> > + base_bitpos &= (base_alignment - 1);
>> >>> > + }
>> >>> > + if (base_bitpos != 0)
>> >>> > + base_alignment = base_bitpos & -base_bitpos;
>> >>> > + /* Also look at the alignment of the base address DR analysis
>> >>> > + computed. */
>> >>> > + unsigned int base_addr_alignment = get_pointer_alignment (base_addr);
>> >>> > + if (base_addr_alignment > base_alignment)
>> >>> > + base_alignment = base_addr_alignment;
>> >>> >
>> >>> > if (base_alignment >= TYPE_ALIGN (TREE_TYPE (vectype)))
>> >>> > DR_VECT_AUX (dr)->base_element_aligned = true;
>> >>>
>> >>> Since you committed this patch (r241892), I'm seeing execution failures:
>> >>> gcc.dg/vect/pr40074.c -flto -ffat-lto-objects execution test
>> >>> gcc.dg/vect/pr40074.c execution test
>> >>> on armeb-none-linux-gnueabihf --with-mode=arm --with-cpu=cortex-a9
>> >>> --with-fpu=neon-fp16
>> >>> (using qemu as simulator)
>> >>
>> >> The difference is that we now vectorize the testcase with versioning
>> >> for alignment (but it should never execute the vectorized variant).
>> >> I need arm peoples help to understand what is wrong.
>> > Hi All,
>> > I will look at it.
>> >
>>
>> Hi,
>>
>> This is causing new regressions on armeb:
>> gcc.dg/vect/vect-strided-a-u8-i2-gap.c -flto -ffat-lto-objects
>> scan-tree-dump-times vect "vectorized 2 loops" 1
>> gcc.dg/vect/vect-strided-a-u8-i2-gap.c scan-tree-dump-times vect
>> "vectorized 2 loops" 1
>
> It's actually an improvement as armeb can't do unaligned loads.
> Before the patch we versioned both loops for alignment (they
> can't be possibly both aligned by luck). After the patch we
> align 'arr' and thus the first loop becomes known-aligned and
> vectorized while the 2nd one is now known unaligned (and thus
> not vectorized because we can't do unaligned accesses).
>
> I suppose the following will fix it. Can you test that on
> some arm variants please?
>
> It works ok on x86_64/i?86 so please commit if it fixes the issue
> for you.
>
Well, it works on armeb (the test now passes), but regresses on
arm-* :(
Christophe
> Thanks,
> Richard.
>
> diff --git a/gcc/testsuite/gcc.dg/vect/vect-strided-a-u8-i2-gap.c b/gcc/testsuite/gcc.dg/vect/vect-strided-a-u8-i2-gap.c
> index 52fdcf6..3752600 100644
> --- a/gcc/testsuite/gcc.dg/vect/vect-strided-a-u8-i2-gap.c
> +++ b/gcc/testsuite/gcc.dg/vect/vect-strided-a-u8-i2-gap.c
> @@ -71,5 +71,5 @@ int main (void)
> return 0;
> }
>
> -/* { dg-final { scan-tree-dump-times "vectorized 2 loops" 1 "vect" { target vect_strided2 } } } */
> -
> +/* { dg-final { scan-tree-dump-times "vectorized 1 loops" 1 "vect" { target { vect_strided2 && { ! vect_hw_misalign } } } } } */
> +/* { dg-final { scan-tree-dump-times "vectorized 2 loops" 1 "vect" { target { vect_strided2 && vect_hw_misalign } } } } */