[Bug rtl-optimization/64682] [5 Regression] wrong code at -O2 and -O3 on x86_64-linux-gnu

["jakub at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64682

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |law at gcc dot gnu.org

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Ah, so the thing is probably that:
(insn 28 27 29 7 (parallel [
            (set (reg:SI 102)
                (udiv:SI (reg:SI 100)
                    (reg:SI 90 [ D.1884 ])))
            (set (reg:SI 101 [ D.1886 ])
                (umod:SI (reg:SI 100)
                    (reg:SI 90 [ D.1884 ])))
            (clobber (reg:CC 17 flags))
        ]) pr64682.c:21 351 {*udivmodsi4}
     (expr_list:REG_DEAD (reg:SI 100)
        (expr_list:REG_DEAD (reg:SI 90 [ D.1884 ])
            (expr_list:REG_UNUSED (reg:SI 102)
                (expr_list:REG_UNUSED (reg:CC 17 flags)
                    (nil))))))
(insn 29 28 30 7 (parallel [
            (set (reg:SI 90 [ D.1884 ])
                (ior:SI (reg:SI 101 [ D.1886 ])
                    (const_int 5 [0x5])))
            (clobber (reg:CC 17 flags))
        ]) pr64682.c:21 398 {*iorsi_1}
     (expr_list:REG_DEAD (reg:SI 101 [ D.1886 ])
        (expr_list:REG_UNUSED (reg:CC 17 flags)
            (nil))))
(insn 30 29 31 7 (set (mem/c:SI (symbol_ref:DI ("b") [flags 0x2] <var_decl
0x7ffff1867cf0 b>) [1 b+0 S4 A32])
        (reg:SI 90 [ D.1884 ])) pr64682.c:21 90 {*movsi_internal}
     (nil))
we combine these 3 into:
(note 28 27 29 7 NOTE_INSN_DELETED)
(insn 29 28 30 7 (set (reg:SI 90 [ D.1884 ])
        (const_int 5 [0x5])) pr64682.c:21 90 {*movsi_internal}
     (nil))
(insn 30 29 31 7 (set (mem/c:SI (symbol_ref:DI ("b") [flags 0x2] <var_decl
0x7ffff1867cf0 b>) [1 b+0 S4 A32])
        (const_int 5 [0x5])) pr64682.c:21 90 {*movsi_internal}
     (nil))
and then try to distribute notes, and as there was a REG_DEAD note for pseudo
90 (correct IMHO) in insn 28, but insn 29 set it again to something else, when
we try to distribute the REG_DEAD note onto the new insn 29 (or 30), we delete
insn 29 as dead.  Giving up, not familiar enough with the dead note
distribution in the combiner.