[Bug debug/103808] [12 Regression] '-fcompare-debug' failure (length) w/ -O2 -ftrapv since r12-5944-ga7acb6dca941db2b

["cvs-commit at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

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 <jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:52441f18db7e051c16f2e6e12f415b93cb5450c4

commit r12-6153-g52441f18db7e051c16f2e6e12f415b93cb5450c4
Author: Jakub Jelinek <jakub@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  <jakub@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.