[Bug rtl-optimization/82628] [8 Regression] wrong code at -Os on x86_64-linux-gnu in the 32-bit mode

[ubizjak at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82628

Uroš Bizjak <ubizjak at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |segher at gcc dot gnu.org
          Component|tree-optimization           |rtl-optimization

--- Comment #3 from Uroš Bizjak <ubizjak at gmail dot com> ---
Looks like combine failure to me:

---cut here--
(insn 17 15 18 4 (set (reg:SI 93)
        (const_int 1 [0x1])) "pr82628.c":14 82 {*movsi_internal}
     (nil))
...
(insn 19 18 20 4 (set (reg:CC 17 flags)
        (compare:CC (reg:SI 93)
            (subreg:SI (reg/v:DI 89 [ d ]) 0))) "pr82628.c":14 7 {*cmpsi_1}
     (expr_list:REG_DEAD (reg:SI 93)
        (expr_list:REG_EQUAL (compare:CC (const_int 1 [0x1])
                (subreg:SI (reg/v:DI 89 [ d ]) 0))
            (nil))))
(insn 20 19 21 4 (parallel [
            (set (reg:CCGZ 17 flags)
                (compare:CCGZ (reg:SI 94)
                    (plus:SI (ltu:SI (reg:CC 17 flags)
                            (const_int 0 [0]))
                        (subreg:SI (reg/v:DI 89 [ d ]) 4))))
            (clobber (scratch:SI))
        ]) "pr82628.c":14 307 {subsi3_carry_ccgz}
     (expr_list:REG_DEAD (reg:SI 94)
        (expr_list:REG_EQUAL (compare:CCGZ (const_int 0 [0])
                (plus:SI (ltu:SI (reg:CC 17 flags)
                        (const_int 0 [0]))
                    (subreg:SI (reg/v:DI 89 [ d ]) 4)))
            (nil))))
(jump_insn 21 20 22 4 (set (pc)
        (if_then_else (geu (reg:CCGZ 17 flags)
                (const_int 0 [0]))
            (label_ref 16)
            (pc))) "pr82628.c":14 664 {*jcc}
     (expr_list:REG_DEAD (reg:CCGZ 17 flags)
        (int_list:REG_BR_PROB 912680552 (nil)))
 -> 16)
---cut here--

combines with:

Trying 17 -> 19:
Successfully matched this instruction:
(set (reg:CC 17 flags)
    (compare:CC (subreg:SI (reg/v:DI 89 [ d ]) 0)
        (const_int 1 [0x1])))

and further with:

Trying 19 -> 20:

Successfully matched this instruction:
(set (pc)
    (label_ref 16))

I don't think that combining:

(set (reg:CC 17 flags)
    (compare:CC (subreg:SI (reg/v:DI 89 [ d ]) 0)
        (const_int 1 [0x1])))

with

(insn 20 19 21 4 (parallel [
            (set (reg:CCGZ 17 flags)
                (compare:CCGZ (reg:SI 94)
                    (plus:SI (ltu:SI (reg:CC 17 flags)
                            (const_int 0 [0]))
                        (subreg:SI (reg/v:DI 89 [ d ]) 4))))
            (clobber (scratch:SI))

should result in unconditional jump:

(set (pc)
    (label_ref 16))