[Bug target/84530] New: -mfunction-return=thunk does not work for simple_return_pop_internal insn

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84530

            Bug ID: 84530
           Summary: -mfunction-return=thunk does not work for
                    simple_return_pop_internal insn
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: marxin at gcc dot gnu.org
                CC: hjl at gcc dot gnu.org, hubicka at ucw dot cz
  Target Milestone: ---
            Target: i586

i386.md contains:

 13100  (define_insn "simple_return_pop_internal"
 13101    [(simple_return)
 13102     (use (match_operand:SI 0 "const_int_operand"))]
 13103    "reload_completed"
 13104    "%!ret\t%0"
 13105    [(set_attr "length" "3")
 13106     (set_attr "atom_unit" "jeu")
 13107     (set_attr "length_immediate" "2")
 13108     (set_attr "modrm" "0")
 13109     (set_attr "maybe_prefix_bnd" "1")])

Thus:

$ cat stdarg.c 
struct s { _Complex unsigned short x; };
struct s gs = { 100 + 200i };
struct s __attribute__((noinline)) foo (void) { return gs; }

$ gcc stdarg.c -S -O2 -m32 -o/dev/stdout  -mfunction-return=thunk
        .file   "stdarg.c"
        .text
        .p2align 4,,15
        .globl  foo
        .type   foo, @function
foo:
.LFB0:
        .cfi_startproc
        movl    4(%esp), %eax
        movl    gs, %edx
        movl    %edx, (%eax)
        ret     $4
        .cfi_endproc
.LFE0:
        .size   foo, .-foo
        .globl  gs
        .data
        .align 4
        .type   gs, @object
        .size   gs, 4
gs:
        .value  100
        .value  200
        .ident  "GCC: (GNU) 8.0.1 20180223 (experimental)"
        .section        .note.GNU-stack,"",@progbits

While x86-64 works:
gcc stdarg.c -S -O2  -o/dev/stdout  -mfunction-return=thunk
        .file   "stdarg.c"
        .text
        .p2align 4,,15
        .globl  foo
        .type   foo, @function
foo:
.LFB0:
        .cfi_startproc
        movzwl  gs+2(%rip), %eax
        sall    $16, %eax
        movl    %eax, %edx
        movzwl  gs(%rip), %eax
        orl     %edx, %eax
        jmp     __x86_return_thunk
        .cfi_endproc
.LFE0:
        .size   foo, .-foo
        .globl  gs
        .data
        .align 2
        .type   gs, @object
        .size   gs, 4
gs:
        .value  100
        .value  200
        .section       
.text.__x86_indirect_thunk,"axG",@progbits,__x86_indirect_thunk,comdat
        .globl  __x86_indirect_thunk
        .hidden __x86_indirect_thunk
        .type   __x86_indirect_thunk, @function
__x86_indirect_thunk:
        .set    __x86_return_thunk,__x86_indirect_thunk
        .globl  __x86_return_thunk
        .hidden __x86_return_thunk
.LFB1:
        .cfi_startproc
        call    .LIND1
.LIND0:
        pause
        lfence
        jmp     .LIND0
.LIND1:
        lea     8(%rsp), %rsp
        ret
        .cfi_endproc
.LFE1:
        .ident  "GCC: (GNU) 8.0.1 20180223 (experimental)"
        .section        .note.GNU-stack,"",@progbits