Re: [PATCH] PR middle-end/126775: ICE optimizing (T)0.0 - x with -ffinite-math-only

On Wed, Aug 19, 2026 at 10:22 PM Roger Sayle <[email protected]> wrote:
>
>
> This patch fixes PR middle-end/126775, an ICE caused by my recent change
> to match.pd around tweaking the conditions under which 0.0 - x can
> safely be transformed into -x.  Unfortunately, that change assumed
> that real_zerop@0 implies that TREE_CODE(@0) == REAL_CST.  Alas things
> aren't that simple, so this fix introduces a new real_negzerop predicate
> that in addition to REAL_CST also handles VECTOR_CST and COMPLEX_CST,
> and most importantly fails gracefully on TREE_CODEs that it isn't
> expecting.
>
> This patch has been tested on x86_64-pc-linux-gnu with make bootstrap
> and make -k check, both with and without --target_board=unix{-m32}
> with no new failures.  Ok for mainline?

OK.

Thanks,
Richard.

>
> 2026-08-19  Roger Sayle  <[email protected]>
>
> gcc/ChangeLog
>         PR middle-end/126775
>         * match.pd (0.0 - x -> -x): Use new real_negzerop function.
>         * tree.cc (real_negzerop): New predicate function to test if
>         a tree expression is -0.0 or equivalent (like real_zerop).
>         * tree.h (real_negzerop): Prototype here.
>
> gcc/testsuite/ChangeLog
>         PR middle-end/126775
>         * gcc.dg/pr126775.c: New test case.
>
>
> Thanks again, and apologies for any inconvenice.
> Roger
> --
>