Hi Richard,
On 7 November 2016 at 09:01, Richard Biener <rguent...@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 <rguent...@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)
Christophe
