On Mon, Apr 29, 2024 at 8:52 AM Andrew Pinski wrote:
>
> While moving value replacement part of PHIOPT over
> to use match-and-simplify, I ran into the case where
> we would have an undef use that was conditional become
> unconditional. This prevents that. I can't remember at this
> point what the testcase was though.
>
> Bootstrapped and tested on x86_64-linux-gnu with no regressions.
OK.
Thanks,
Richard.
> gcc/ChangeLog:
>
> * tree-ssa-phiopt.cc (value_replacement): Reject undef variables
> so they don't become unconditional used.
>
> Signed-off-by: Andrew Pinski
> ---
> gcc/tree-ssa-phiopt.cc | 7 +++
> 1 file changed, 7 insertions(+)
>
> diff --git a/gcc/tree-ssa-phiopt.cc b/gcc/tree-ssa-phiopt.cc
> index a2bdcb5eae8..f166c3132cb 100644
> --- a/gcc/tree-ssa-phiopt.cc
> +++ b/gcc/tree-ssa-phiopt.cc
> @@ -1146,6 +1146,13 @@ value_replacement (basic_block cond_bb, basic_block
> middle_bb,
>if (code != NE_EXPR && code != EQ_EXPR)
> return 0;
>
> + /* Do not make conditional undefs unconditional. */
> + if ((TREE_CODE (arg0) == SSA_NAME
> + && ssa_name_maybe_undef_p (arg0))
> + || (TREE_CODE (arg1) == SSA_NAME
> + && ssa_name_maybe_undef_p (arg1)))
> +return false;
> +
>/* If the type says honor signed zeros we cannot do this
> optimization. */
>if (HONOR_SIGNED_ZEROS (arg1))
> --
> 2.43.0
>
