https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105116
--- Comment #3 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:d00acdc3ecff20ce0591103364be86505c382af6 commit r17-1954-gd00acdc3ecff20ce0591103364be86505c382af6 Author: Kyrylo Tkachov <[email protected]> Date: Wed Jun 17 07:25:31 2026 -0700 LRA: reload non-representable subregs of hard registers through memory [PR105116] PR target/105116 is an aarch64 ICE in lra_split_hard_reg_for ("unable to find a register to spill"). A wide vector value (OImode, a pair of Q registers) is pinned to FP registers via asm register variables and an operation with no Advanced SIMD form (an integer vector divide or modulo) is scalarised by vector lowering. The scalar pieces read non-lowpart scalar subregs of the OImode register, e.g. (subreg:DI (reg:OI v2) 8), the high 64 bits of the first Q register. Such a subreg is not representable as a hard register (subreg_get_info returns representable_p == false), but the hard-register branch of simplify_operand_subreg only called alter_subreg, which resolves it to the wrong part of the register. For GENERAL_REGS uses, curr_insn_transform then tried to reload the whole OImode inner register into GENERAL_REGS, which is impossible (aarch64_hard_regno_mode_ok is false for OImode in GENERAL_REGS) and gave the ICE; for FP-context uses the bad subreg survived to final and silently read the wrong bytes (a latent wrong-code bug). Handle this in simplify_operand_subreg: when a narrowing subreg of a hard register is not representable, reload the inner register through memory (NO_REGS) so that the correct bytes are accessed, mirroring the existing handling for pseudos. The frame, arg and stack pointers are left alone, as simplify_subreg_regno can reject them merely because reload is not finished. This only affects the already non-representable case; representable subregs are unchanged. Bootstrapped and tested on aarch64-none-linux-gnu and x86_64-linux. Signed-off-by: Kyrylo Tkachov <[email protected]> gcc/ChangeLog: PR target/105116 * lra-constraints.cc (simplify_operand_subreg): Reload a non-representable narrowing subreg of a hard register through memory instead of resolving it lossily. gcc/testsuite/ChangeLog: PR target/105116 * gcc.target/aarch64/sve/pr105116.c: New test. * gcc.target/aarch64/sve/pr105116-run.c: New test.
