On Tue, Apr 13, 2021 at 3:50 PM Richard Biener <rguent...@suse.de> wrote:
>
> This adds disambiguation of the access size vs. the decl size
> in the pointer based vs. decl based disambiguator. We have
> a TBAA based check like this already but that's fend off when
> seeing alias-sets of zero or when -fno-strict-aliasing is in
> effect. Also the perceived dynamic type could be smaller than
> the actual access.
>
> Bootstrapped and tested on x86_64-unknown-linux-gnu, queued for stage1.
g:d1d01a66012a93cc8cb7dafbe1b5ec453ec96b59
> 2021-04-13 Richard Biener <rguent...@suse.de>
>
> PR tree-optimization/100051
> * tree-ssa-alias.c (indirect_ref_may_alias_decl_p): Add
> disambiguator based on access size vs. decl size.
>
> * gcc.dg/tree-ssa/ssa-fre-92.c: New testcase.
> ---
> gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-92.c | 21 +++++++++++++++++++++
> gcc/tree-ssa-alias.c | 11 +++++++++++
> 2 files changed, 32 insertions(+)
> create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-92.c
>
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-92.c
> b/gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-92.c
> new file mode 100644
> index 00000000000..c67fcea5e93
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-92.c
> @@ -0,0 +1,21 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -fdump-tree-fre1" } */
> +
> +extern void foo(void);
> +int a, c, *f, **d = &f;
> +char b;
> +int main()
> +{
> + if (a) {
> + b = 0;
> + int *g = &c;
> + *g = 0;
> + f = *d;
> + *d = f;
> + if ((2 ^ b) == 0)
> + foo();
> + }
> + return 0;
> +}
> +
> +/* { dg-final { scan-tree-dump-not "foo" "fre1" } } */
> diff --git a/gcc/tree-ssa-alias.c b/gcc/tree-ssa-alias.c
> index ebb3f49c86c..6c7d2f1b7e0 100644
> --- a/gcc/tree-ssa-alias.c
> +++ b/gcc/tree-ssa-alias.c
> @@ -2034,6 +2034,17 @@ indirect_ref_may_alias_decl_p (tree ref1
> ATTRIBUTE_UNUSED, tree base1,
> if (TREE_CODE (base1) != TARGET_MEM_REF
> && !ranges_maybe_overlap_p (offset1 + moff, -1, offset2, max_size2))
> return false;
> +
> + /* If the pointer based access is bigger than the variable they cannot
> + alias. This is similar to the check below where we use TBAA to
> + increase the size of the pointer based access based on the dynamic
> + type of a containing object we can infer from it. */
> + poly_int64 dsize2;
> + if (known_size_p (size1)
> + && poly_int_tree_p (DECL_SIZE (base2), &dsize2)
> + && known_lt (dsize2, size1))
> + return false;
> +
> /* They also cannot alias if the pointer may not point to the decl. */
> if (!ptr_deref_may_alias_decl_p (ptr1, base2))
> return false;
> --
> 2.26.2
