[PATCH] vrp: Handle pointers in maybe_set_nonzero_bits [PR108253]

[Aldy Hernandez]

On PTO until Monday but thinking out loud here....

Shouldn't we put this code in set_nonzero_bits instead, and leave maybe*
alone? That way any possible setters may benefit from your change?

Also, havent looked (AFK) but does this change work with the global range
getter (get_global_range_query...)?

Thoughts?

Aldy


On Wed, Jan 4, 2023, 10:13 Jakub Jelinek <jakub@redhat.com> wrote:

> Hi!
>
> maybe_set_nonzero_bits calls set_nonzero_bits which asserts that
> var doesn't have pointer type.  While we could punt for those
> cases, I think we can handle at least some easy cases.
> Earlier in maybe_set_nonzero_bits we've checked this is on
> (var & cst) == 0
> edge and the other edge is __builtin_unreachable, so if cst
> is say 3 as in the testcase, we want to turn it into 4 byte alignment
> of the pointer.
>
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
>
> 2023-01-04  Jakub Jelinek  <jakub@redhat.com>
>
>         PR tree-optimization/108253
>         * tree-vrp.cc (maybe_set_nonzero_bits): Handle var with pointer
>         types.
>
>         * g++.dg/opt/pr108253.C: New test.
>
> --- gcc/tree-vrp.cc.jj  2023-01-02 09:32:53.634833769 +0100
> +++ gcc/tree-vrp.cc     2023-01-03 15:57:51.613239761 +0100
> @@ -789,8 +789,22 @@ maybe_set_nonzero_bits (edge e, tree var
>         return;
>      }
>    cst = gimple_assign_rhs2 (stmt);
> -  set_nonzero_bits (var, wi::bit_and_not (get_nonzero_bits (var),
> -                                         wi::to_wide (cst)));
> +  if (POINTER_TYPE_P (TREE_TYPE (var)))
> +    {
> +      struct ptr_info_def *pi = SSA_NAME_PTR_INFO (var);
> +      if (pi && pi->misalign)
> +       return;
> +      wide_int w = wi::bit_not (wi::to_wide (cst));
> +      unsigned int bits = wi::ctz (w);
> +      if (bits == 0 || bits >= HOST_BITS_PER_INT)
> +       return;
> +      unsigned int align = 1U << bits;
> +      if (pi == NULL || pi->align < align)
> +       set_ptr_info_alignment (get_ptr_info (var), align, 0);
> +    }
> +  else
> +    set_nonzero_bits (var, wi::bit_and_not (get_nonzero_bits (var),
> +                                           wi::to_wide (cst)));
>  }
>
>  /* Searches the case label vector VEC for the index *IDX of the CASE_LABEL
> --- gcc/testsuite/g++.dg/opt/pr108253.C.jj      2023-01-03
> 16:02:16.366438488 +0100
> +++ gcc/testsuite/g++.dg/opt/pr108253.C 2023-01-03 16:02:33.549191780 +0100
> @@ -0,0 +1,48 @@
> +// PR tree-optimization/108253
> +// { dg-do compile { target c++11 } }
> +// { dg-options "-O2" }
> +
> +struct S
> +{
> +  int *s;
> +  S () : s (new int) {}
> +  S (const S &r) noexcept : s (r.s) { __atomic_fetch_add (r.s, 1, 4); }
> +};
> +struct T
> +{
> +  explicit T (const S &x) : t (x) {}
> +  const S t;
> +};
> +struct U
> +{
> +  operator int () const { new T (u); return 0; }
> +  S u;
> +};
> +bool foo (int matcher);
> +unsigned long bar (unsigned long pos, unsigned long end_pos);
> +struct V
> +{
> +  alignas (4) char v[4];
> +};
> +struct W
> +{
> +  void baz ()
> +  {
> +    if (!w) __builtin_abort ();
> +    if (reinterpret_cast <__UINTPTR_TYPE__> (w->v) % 4 != 0)
> __builtin_abort ();
> +    __builtin_unreachable ();
> +  }
> +  [[gnu::noinline]] void qux (unsigned long) { if (!w) bar (0, x); }
> +  V *w = nullptr;
> +  unsigned x = 0;
> +};
> +
> +void
> +test ()
> +{
> +  W w;
> +  U t;
> +  if (!foo (t))
> +    w.baz ();
> +  w.qux (0);
> +}
>
>         Jakub
>
>