[Bug c++/58192] G++ emits incorrect code when passing enum classes as function parameters

["ubizjak at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58192

--- Comment #9 from UroÅ Bizjak <ubizjak at gmail dot com> ---
Looking at dumps, obtained with -m32 -O1, we have following sequence before the
call to _ZN2S1Ut_3setE3Foo:

_.dfinit:

(insn 7 3 8 2 (parallel [
            (set (reg:SI 88)
                (lshiftrt:SI (reg/v:SI 86 [ t ])
                    (const_int 16 [0x10])))
            (clobber (reg:CC 17 flags))
        ]) 539 {*lshrsi3_1}
     (nil))
(insn 8 7 9 2 (parallel [
            (set (reg:QI 85 [ t$2 ])
                (and:QI (subreg:QI (reg:SI 88) 0)
                    (const_int -1 [0xffffffffffffffff])))
            (clobber (reg:CC 17 flags))
        ]) 379 {*andqi_1}
     (nil))

...

(insn 10 9 11 2 (set (reg:QI 1 dx)
        (reg:QI 85 [ t$2 ])) gcc-bug.cc:72 93 {*movqi_internal}
     (nil))

...

(call_insn 12 11 13 2 (call (mem:QI (symbol_ref:SI ("_ZN2S1Ut_3setE3Foo")
[flags 0x3]  <function_decl 0x2ad94c491438 set>) [0 set S1 A8])
        (const_int 0 [0])) gcc-bug.cc:72 651 {*call}
     (expr_list:REG_EH_REGION (const_int 0 [0])
        (nil))
    (expr_list:SI (use (reg:SI 0 ax))
        (expr_list:QI (use (reg:QI 1 dx))
            (nil))))

_.cse1 mangles argument setup to:

(insn 8 7 9 2 (set (reg:QI 85 [ t$2 ])
        (subreg:QI (reg:SI 88) 0)) 93 {*movqi_internal}
     (expr_list:REG_DEAD (reg:SI 88)
        (expr_list:REG_UNUSED (reg:CC 17 flags)
            (nil))))

...

(insn 10 9 11 2 (set (reg:QI 1 dx)
        (subreg:QI (reg:SI 88) 0)) gcc-bug.cc:72 93 {*movqi_internal}
     (nil))

and _.fwprop1 merges both to:

(insn 10 9 11 2 (set (reg:QI 1 dx)
        (subreg:QI (reg:SI 88) 0)) gcc-bug.cc:72 93 {*movqi_internal}
     (nil))

resulting in:

#(insn 10 9 34 2 (set (reg:QI 1 dx)
#        (reg:QI 3 bx [88])) gcc-bug.cc:72 93 {*movqi_internal}
#     (nil))
    movl    %ebx, %edx    # 10    *movqi_internal/1    [length = 2]

However, x86 ABI mandates that arguments should be properly extended in the
call to the function. I don't think original (insn 8) is correct, as it is
effectively a NOP.