https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103808
--- Comment #6 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Jakub Jelinek <ja...@gcc.gnu.org>: https://gcc.gnu.org/g:52441f18db7e051c16f2e6e12f415b93cb5450c4 commit r12-6153-g52441f18db7e051c16f2e6e12f415b93cb5450c4 Author: Jakub Jelinek <ja...@redhat.com> Date: Thu Dec 30 14:35:06 2021 +0100 emit-rtl: Fix a -fcompare-debug issue due to var-tracking [PR103808] We get a -fcompare-debug FAIL on the following testcase. The problem is that during cprop we get when a TImode pseudo holding x is being constructed: (debug_insn 111 59 103 7 (var_location:TI D#2 (clobber (const_int 0 [0]))) -1 (nil)) (insn 103 111 110 7 (clobber (reg/v:TI 89 [ x ])) "pr103808.c":8:9 -1 (nil)) (debug_insn 110 103 104 7 (var_location:TI D#2 (subreg:TI (reg:DI 111 [ x ]) 0)) -1 (nil)) (insn 104 110 109 7 (set (subreg:DI (reg/v:TI 89 [ x ]) 0) (reg:DI 111 [ x ])) "pr103808.c":8:9 80 {*movdi_internal} (expr_list:REG_DEAD (reg:DI 111 [ x ]) (nil))) Now, during RA that paradoxical subreg in a debug insn obviously can't affect where pseudo 111 is allocated and RA puts it into the bp register, so we have: (debug_insn 110 111 109 4 (var_location:TI D#2 (reg:TI 6 bp [orig:111 x ] [111])) -1 (nil)) Now, during var-tracking when we for: (debug_insn 25 23 26 3 (var_location:TI x (concatn/v:TI [ (reg:DI 6 bp [orig:111 x ] [111]) (subreg:DI (debug_expr:TI D#2) 8) ])) "pr103808.c":8:9 -1 (nil)) try to simplify the highpart subreg of bp, gen_rtx_REG_offset is called in: if (HARD_REGISTER_NUM_P (final_regno)) { rtx x = gen_rtx_REG_offset (op, outermode, final_regno, subreg_memory_offset (outermode, innermode, byte)); and that unfortunately sets REG_ATTRS on stack_pointer_rtx, because gen_rtx_REG_offset uses gen_rtx_REG which for Pmode STACK_POINTER_REGNUM returns stack_pointer_rtx rather than newly created register. The clobbering of REG_ATTRS on the shared stack_pointer_rtx then shows up in the dumps as (reg/f:DI 7 sp [ x+8 ]) instead of (reg/f:DI 7 sp) that shows up without var-tracking. Clobbering of REG_ATTRS on the shared *_pointer_rtx looks just wrong. So, IMHO either simplify_gen_subreg -> gen_rtx_REG_offset should call gen_raw_REG to make sure we get a new non-shared REG we can set REG_ATTRS on, or we should make sure that we don't overwrite the REG_ATTRS on the shared REGs (but then simplify_gen_subreg shouldn't try to overwrite ORIGINAL_REGNO on those either). For non-DEBUG_INSNs, I'd hope this never happens, the RA shouldn't allocate multi-word regs overlapping with stack pointer, hard frame pointer etc. 2021-12-30 Jakub Jelinek <ja...@redhat.com> PR debug/103808 * emit-rtl.c (gen_rtx_REG_offset): Use gen_raw_REG instead of gen_rtx_REG. * gcc.dg/pr103808.c: New test.
