https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116389
--- Comment #10 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The releases/gcc-15 branch has been updated by Georg-Johann Lay <g...@gcc.gnu.org>: https://gcc.gnu.org/g:61789b5abec3079d02ee9eaa7468015ab1f6f701 commit r15-9837-g61789b5abec3079d02ee9eaa7468015ab1f6f701 Author: Georg-Johann Lay <a...@gjlay.de> Date: Sat Jun 14 19:57:18 2025 +0200 AVR: Fix PR120423 / PR116389. The problem with PR120423 and PR116389 is that reload might assign an invalid hard register to a paradoxical subreg. For example with the test case from the PR, it assigns (REG:QI 31) to the inner of (subreg:HI (QI) 0) which is valid, but the subreg will be turned into (REG:HI 31) which is invalid and triggers an ICE in postreload. The problem only occurs with the old reload pass. The patch maps the paradoxical subregs to a zero-extends which will be allocated correctly. For the 120423 testcases, the code is the same like with -mlra (which doesn't implement the fix), so the patch doesn't even introduce a performance penalty. The patch is only needed for v15: v14 is not affected, and in v16 reload will be removed. PR rtl-optimization/120423 PR rtl-optimization/116389 gcc/ * config/avr/avr.md [-mno-lra]: Add pre-reload split to transform (left shift of) a paradoxical subreg to a (left shift of) zero-extend. gcc/testsuite/ * gcc.target/avr/torture/pr120423-1.c: New test. * gcc.target/avr/torture/pr120423-2.c: New test. * gcc.target/avr/torture/pr120423-116389.c: New test.
