[Bug rtl-optimization/79450] [5/6/7 Regression] wrong code with loop at -O1

[ubizjak at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79450

Uroš Bizjak <ubizjak at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|target                      |rtl-optimization

--- Comment #2 from Uroš Bizjak <ubizjak at gmail dot com> ---
(In reply to Jakub Jelinek from comment #1)

> Things go wrong during combine.

(insn 34 33 35 4 (set (reg:SI 116 [ p1 ])
        (zero_extend:SI (reg/v:QI 96 [ p1 ]))) "pr79450.c":14 134
{*zero_extendqisi2}
     (expr_list:REG_DEAD (reg/v:QI 96 [ p1 ])
        (nil)))
(insn 35 34 40 4 (parallel [
            (set (reg:SI 115)
                (plus:SI (reg:SI 116 [ p1 ])
                    (subreg:SI (reg/v:DI 98 [ p2 ]) 0)))
            (clobber (reg:CC 17 flags))
        ]) "pr79450.c":14 215 {*addsi_1}
     (expr_list:REG_DEAD (reg:SI 116 [ p1 ])
        (expr_list:REG_DEAD (reg/v:DI 98 [ p2 ])
            (expr_list:REG_UNUSED (reg:CC 17 flags)
                (nil)))))

combine converts this to:

Trying 34 -> 35:
Failed to match this instruction:
(parallel [
        (set (reg:SI 115)
            (subreg:SI (reg/v:DI 98 [ p2 ]) 0))
        (clobber (reg:CC 17 flags))
    ])
Successfully matched this instruction:
(set (reg:SI 115)
    (subreg:SI (reg/v:DI 98 [ p2 ]) 0))
allowing combination of insns 34 and 35