https://gcc.gnu.org/bugzilla/show_bug.cgi?id=127483
--- Comment #2 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Kyrylo Tkachov <[email protected]>: https://gcc.gnu.org/g:486c6296ed318d0df27a053d2288b6f4fa47517d commit r17-4989-g486c6296ed318d0df27a053d2288b6f4fa47517d Author: Kyrylo Tkachov <[email protected]> Date: Wed Oct 7 17:29:35 2026 +0200 simplify-rtx: Fix ICE in the VEC_CONCAT halves fold [PR127483] simplify_binary_operation_1 simplifies the concatenation of the two halves of an object to gen_lowpart of the object. get_ref_base_and_offset can return any rtx as the object, such as an UNSPEC, but gen_lowpart asserts for an UNSPEC in another mode. For example, on AArch64 fwprop1 tries to propagate the result of an LD2 into the operands of an ADDP for: uint8x8x2_t v = vld2_u8 (p); return vpadd_u8 (v.val[0], v.val[1]); The ADDP operands then contain: (vec_concat:V16QI (subreg:V8QI (unspec:V2x8QI [(mem:V2x8QI (reg:DI p))] UNSPEC_LD2_DREG) 0) (subreg:V8QI (unspec:V2x8QI [(mem:V2x8QI (reg:DI p))] UNSPEC_LD2_DREG) 8)) and gen_lowpart (V16QImode, (unspec:V2x8QI ...)) fails the assert. The x86_64 testcase in the PR reaches the fold through debug insns. Use rtl_hooks.gen_lowpart_no_emit, like the other simplifications in this file, and do not fold if it fails. Unlike gen_lowpart, the hook also never emits instructions. Bootstrapped and tested on x86_64-pc-linux-gnu. gcc/ChangeLog: PR rtl-optimization/127483 * simplify-rtx.cc (simplify_context::simplify_binary_operation_1) <case VEC_CONCAT>: Use rtl_hooks.gen_lowpart_no_emit rather than gen_lowpart, and do not fold if it fails. gcc/testsuite/ChangeLog: PR rtl-optimization/127483 * gcc.dg/pr127483.c: New test. * gcc.target/aarch64/pr127483.c: Likewise. * gcc.target/aarch64/pr127483-be.c: Likewise. Signed-off-by: Kyrylo Tkachov <[email protected]>
