Re: [PATCH] reassoc: Fix up another ICE with returns_twice call [PR109410]

[Richard Biener <rguenther@suse.de>]

> Am 12.04.2023 um 16:37 schrieb Jakub Jelinek via Gcc-patches <gcc-patches@gcc.gnu.org>:
> 
> Hi!
> 
> The following testcase ICEs in reassoc, unlike the last case I've fixed
> there here SSA_NAME_USED_IN_ABNORMAL_PHI is not the case anywhere.
> build_and_add_sum places new statements after the later appearing definition
> of an operand but if both operands are default defs or constants, we place
> statement at the start of the function.
> 
> If the very first statement of a function is a call to returns_twice
> function, this doesn't work though, because that call has to be the first
> thing in its basic block, so the following patch splits the entry successor
> edge such that the new statements are added into a different block from the
> returns_twice call.
> 
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

Ok.

> I think we should in stage1 reconsider such placements, I think it
> unnecessarily enlarges the lifetime of the new lhs if its operand(s)
> are used more than once in the function.  Unless something sinks those
> again.  Would be nice to place it closer to the actual uses (or where
> they will be placed).

IStR there is code to do that in reassoc already.

> 
> 2023-04-12  Jakub Jelinek  <jakub@redhat.com>
> 
>    PR tree-optimization/109410
>    * tree-ssa-reassoc.cc (build_and_add_sum): Split edge from entry
>    block if first statement of the function is a call to returns_twice
>    function.
> 
>    * gcc.dg/pr109410.c: New test.
> 
> --- gcc/tree-ssa-reassoc.cc.jj    2023-02-18 12:40:42.739131728 +0100
> +++ gcc/tree-ssa-reassoc.cc    2023-04-12 13:23:49.083979843 +0200
> @@ -1564,6 +1564,15 @@ build_and_add_sum (tree type, tree op1,
>       && (!op2def || gimple_nop_p (op2def)))
>     {
>       gsi = gsi_after_labels (single_succ (ENTRY_BLOCK_PTR_FOR_FN (cfun)));
> +      if (!gsi_end_p (gsi)
> +      && is_gimple_call (gsi_stmt (gsi))
> +      && (gimple_call_flags (gsi_stmt (gsi)) & ECF_RETURNS_TWICE))
> +    {
> +      /* Don't add statements before a returns_twice call at the start
> +         of a function.  */
> +      split_edge (single_succ_edge (ENTRY_BLOCK_PTR_FOR_FN (cfun)));
> +      gsi = gsi_after_labels (single_succ (ENTRY_BLOCK_PTR_FOR_FN (cfun)));
> +    }
>       if (gsi_end_p (gsi))
>    {
>      gimple_stmt_iterator gsi2
> --- gcc/testsuite/gcc.dg/pr109410.c.jj    2023-04-12 13:42:41.759751843 +0200
> +++ gcc/testsuite/gcc.dg/pr109410.c    2023-04-12 13:42:27.249959585 +0200
> @@ -0,0 +1,19 @@
> +/* PR tree-optimization/109410 */
> +/* { dg-do compile } */
> +/* { dg-options "-O2" } */
> +
> +__attribute__((returns_twice)) int baz (int, int);
> +
> +int
> +bar (int x)
> +{
> +  return x;
> +}
> +
> +int
> +foo (int x, int y)
> +{
> +  baz (x, y);
> +  int a = bar (x);
> +  return y || a == 42 || a > 42;
> +}
> 
>    Jakub
>