https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126788
--- Comment #3 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Richard Biener <[email protected]>: https://gcc.gnu.org/g:465ee014cb0cf9be62f0fd3de3821c755d37f58d commit r17-3331-g465ee014cb0cf9be62f0fd3de3821c755d37f58d Author: Richard Biener <[email protected]> Date: Thu Aug 13 14:57:56 2026 +0200 middle-end/126788 - more vector folding The last match.pd update for double-conversion folding didn't handle the case where a vector conversion would go away because supportable_convert_operation doesn't consider a noop conversion (or a sign conversion). The following rectifies this, allowing a NOP_EXPR and VIEW_CONVERT_EXPR for same mode types as supportable conversion as we can RTL expand that just fine. This shows that the vectorizer routed sign-conversions through vectorizable_assignment but now vectorizable_conversion would handle it, emitting NOP_EXPRs (which is fine) instead of VIEW_CONVERT_EXPRs (which we declared canonical for vectors). This would confuse some foldings, leading to testsuite FAILs, so make vectorizable_conversion also prefer VIEW_CONVERT_EXPRs here. PR middle-end/126788 * optabs-tree.cc (supportable_convert_operation): For same modes allow NOP_EXPR and VIEW_CONVERT_EXPR. * tree-ssa-forwprop.cc (simplify_vector_constructor): Avoid converting the vector to be used for blending into the result to the type of the permutation. * tree-vect-stmts.cc (vectorizable_conversion): Leave nop-conversions to vectorizable_assignment. * gcc.target/i386/pr126788.c: New testcase.
