On Thu, Feb 23, 2017 at 6:49 AM, Jeff Law <l...@redhat.com> wrote:
>
> tree-ssa-dse.c needs to verify when two writes have the same base address.
> Right now it uses pointer equality. The testcase in BZ79578 shows that we
> should have been using operand_equal_p.
>
> This one-liner fixes that oversight. Bootstrapped and regression tested on
> x86_64-linux-gnu. Installed on the trunk.
>
> Jeff
>
> commit ef506ec9114a7fe27d9ee892c17edd100f72a963
> Author: law <law@138bc75d-0d04-0410-961f-82ee72b054a4>
> Date: Thu Feb 23 05:47:43 2017 +0000
>
> PR tree-optimization/79578
> * tree-ssa-dse.c (clear_bytes_written_by): Use operand_equal_p
> to compare base operands.
>
> PR tree-optimization/79578
> * g++.dg/tree-ssa/ssa-dse-3.C: New test.
>
> git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@245675
> 138bc75d-0d04-0410-961f-82ee72b054a4
>
> diff --git a/gcc/ChangeLog b/gcc/ChangeLog
> index 7155850..6da1d74 100644
> --- a/gcc/ChangeLog
> +++ b/gcc/ChangeLog
> @@ -1,3 +1,9 @@
> +2017-02-22 Jeff Law <l...@redhat.com>
> +
> + PR tree-optimization/79578
> + * tree-ssa-dse.c (clear_bytes_written_by): Use operand_equal_p
> + to compare base operands.
> +
> 2017-02-22 Segher Boessenkool <seg...@kernel.crashing.org>
>
> PR target/79211
> diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
> index ea5e251..d900cc3 100644
> --- a/gcc/testsuite/ChangeLog
> +++ b/gcc/testsuite/ChangeLog
> @@ -1,3 +1,8 @@
> +2017-02-22 Jeff Law <l...@redhat.com>
> +
> + PR tree-optimization/79578
> + * g++.dg/tree-ssa/ssa-dse-3.C: New test.
> +
> 2017-02-22 Sameera Deshpande <sameera.deshpa...@imgtec.com>
>
> * gcc.target/mips/msa-fp-cc.c: New test.
> diff --git a/gcc/testsuite/g++.dg/tree-ssa/ssa-dse-3.C
> b/gcc/testsuite/g++.dg/tree-ssa/ssa-dse-3.C
> new file mode 100644
> index 0000000..fe8f309
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/tree-ssa/ssa-dse-3.C
> @@ -0,0 +1,28 @@
> +/* { dg-do compile } */
> +/* { dg-options "-std=c++14 -O3 -fdump-tree-dse1-details" } */
> +
> +#include <new>
> +#include <cstdint>
> +
> +struct A
> +{
> + std::uint16_t a, b;
> +};
> +
> +A* f(char* b) __attribute__((noinline));
> +
> +A* f(char* b) {
> + auto a = new(b) A{};
> + a->a = 1;
> + a->b = 2;
> + return a;
> +}
> +
> +int main() {
> + char b[sizeof(A)] alignas(A);
> + f(b);
> +}
> +
> +
> +/* { dg-final { scan-tree-dump "Deleted dead store: " "dse1" } } */
> +
> diff --git a/gcc/tree-ssa-dse.c b/gcc/tree-ssa-dse.c
> index 84c0b11..a82e164 100644
> --- a/gcc/tree-ssa-dse.c
> +++ b/gcc/tree-ssa-dse.c
> @@ -176,7 +176,7 @@ clear_bytes_written_by (sbitmap live_bytes, gimple
> *stmt, ao_ref *ref)
> /* Verify we have the same base memory address, the write
> has a known size and overlaps with REF. */
> if (valid_ao_ref_for_dse (&write)
> - && write.base == ref->base
> + && operand_equal_p (write.base, ref->base, 0)
As you've identified size and offset match you are really interested
in comparing the base addresses and thus should use OEP_ADDRESS_OF.
Richard.
> && write.size == write.max_size
> && ((write.offset < ref->offset
> && write.offset + write.size > ref->offset)
>
