Re: [PATCH] tree-ssa-math-opts: Fix up uaddc/usubc pattern matching [PR110271]

[Richard Biener <rguenther@suse.de>]

> Am 16.06.2023 um 16:23 schrieb Jakub Jelinek <jakub@redhat.com>:
> 
> Hi!
> 
> The following testcase ICEs, because I misremembered what the return value
> from match_arith_overflow is.  It isn't true if __builtin_*_overflow was
> matched, but it is true only in the BIT_NOT_EXPR case if stmt was removed.
> 
> So, if match_arith_overflow matches something, gsi_stmt (gsi) will not
> be stmt and match_uaddc_usubc will be confused and can ICE.
> 
> The following patch fixes it by checking if gsi_stmt (gsi) == stmt,
> in that case we know it is still a PLUS_EXPR/MINUS_EXPR and we can try to
> pattern match it further as UADDC/USUBC.
> 
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

Ok

Richard 

> 2023-06-16  Jakub Jelinek  <jakub@redhat.com>
> 
>    PR tree-optimization/110271
>    * tree-ssa-math-opts.cc (math_opts_dom_walker::after_dom_children)
>    <case PLUS_EXPR>: Ignore return value from match_arith_overflow,
>    instead call match_uaddc_usubc only if gsi_stmt (gsi) is still stmt.
> 
>    * gcc.c-torture/compile/pr110271.c: New test.
> 
> --- gcc/tree-ssa-math-opts.cc.jj    2023-06-15 09:12:28.777829348 +0200
> +++ gcc/tree-ssa-math-opts.cc    2023-06-16 10:44:31.231798664 +0200
> @@ -5558,9 +5558,12 @@ math_opts_dom_walker::after_dom_children
> 
>        case PLUS_EXPR:
>        case MINUS_EXPR:
> -          if (!convert_plusminus_to_widen (&gsi, stmt, code)
> -          && !match_arith_overflow (&gsi, stmt, code, m_cfg_changed_p))
> -        match_uaddc_usubc (&gsi, stmt, code);
> +          if (!convert_plusminus_to_widen (&gsi, stmt, code))
> +        {
> +          match_arith_overflow (&gsi, stmt, code, m_cfg_changed_p);
> +          if (gsi_stmt (gsi) == stmt)
> +            match_uaddc_usubc (&gsi, stmt, code);
> +        }
>          break;
> 
>        case BIT_NOT_EXPR:
> --- gcc/testsuite/gcc.c-torture/compile/pr110271.c.jj    2023-06-16 10:57:32.757621687 +0200
> +++ gcc/testsuite/gcc.c-torture/compile/pr110271.c    2023-06-16 10:57:15.298871335 +0200
> @@ -0,0 +1,24 @@
> +/* PR tree-optimization/110271 */
> +
> +unsigned a, b, c, d, e;
> +
> +void
> +foo (unsigned *x, int y, unsigned int *z)
> +{
> +  for (int i = 0; i < y; i++)
> +    {
> +      b += d;
> +      a += b < d;
> +      a += c = (__PTRDIFF_TYPE__) x > 3;
> +      d = z[1] + (a < c);
> +      a += e;
> +      d += a < e;
> +    }
> +}
> +
> +void
> +bar (unsigned int *z)
> +{
> +  unsigned *x = x;
> +  foo (x, 9, z);
> +}
> 
>    Jakub
>