https://gcc.gnu.org/bugzilla/show_bug.cgi?id=55212
--- Comment #481 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Oleg Endo <[email protected]>: https://gcc.gnu.org/g:746bdda47afbbe4b7cf5581e1f6d86824fdc10b6 commit r17-2076-g746bdda47afbbe4b7cf5581e1f6d86824fdc10b6 Author: Kaz Kojima <[email protected]> Date: Fri Oct 18 11:09:37 2024 +0900 LRA: Add cannot_substitute_const_equiv_p target hook On SH fp constant load special instructions 'fldi0' and 'fldi1' are only valid for single-precision fp mode and thus depend on mode-switiching. LRA is not aware of that (or any mode-switching constraints) and would emit such constant loads in the wrong mode by changing fp-move related insn alternative without validating fp-mode attributes. This new target hook allows rejecting such potentially unsafe substitutions. This patch has been proposed here https://gcc.gnu.org/pipermail/gcc-patches/2026-March/709649.html but was initially rejected, as it's just papering over the real problem. Further discussion has clarified that this is a general issue in GCC, not only limited to LRA. Everything that runs after the mode-switching pass can make potentially unsafe insn transformations because nothing is validating the insn mode requirements against the current cpu/fpu mode state. After some reconsideration, this patch was approved https://gcc.gnu.org/pipermail/gcc-patches/2026-June/722024.html gcc/ChangeLog: PR target/117182 PR target/55212 * target.def (cannot_substitute_const_equiv_p): New target hook. * doc/tm.texi.in: Add it. * lra-constraints.cc (get_equiv): Use it. * config/sh/sh.cc (sh_cannot_substitute_const_equiv_p): Override it. * doc/tm.texi: Re-generate.
