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int main(int argc, char** argv) {
    constexpr const char a = 'A';
    // mov eax,65
    // movsx eax, al
    // mov esi, eax
    printf("%c\n",foo<-1>::test());
    // mov esi, 65
    printf("%c\n",a);
    return 0;
}

honey the codewitch wrote:

Yeah, that's not really the issue I'm having though.

main:                                   # @main
        push    rax
        mov     edi, .L.str
        mov     esi, 65
        xor     eax, eax
        call    printf
        mov     edi, .L.str
        mov     esi, 65
        xor     eax, eax
        call    printf
        xor     eax, eax
        pop     rcx
        ret
.L.str:
        .asciz  "%c\n"

.LC0:
        .string "%c\n"
main:
        sub     rsp, 8
        mov     esi, 65
        mov     edi, OFFSET FLAT:.LC0
        mov     eax, 0
        call    printf
        mov     esi, 65
        mov     edi, OFFSET FLAT:.LC0
        mov     eax, 0
        call    printf
        mov     eax, 0
        add     rsp, 8
        ret

main:
.LFB31:
  .cfi_startproc
  endbr64
  subq  $8, %rsp
  .cfi_def_cfa_offset 16
  movl  $65, %edx
  leaq  .LC0(%rip), %rsi
  movl  $1, %edi
  movl  $0, %eax
  call  __printf_chk@PLT
  movl  $65, %edx
  leaq  .LC0(%rip), %rsi
  movl  $1, %edi
  movl  $0, %eax
  call  __printf_chk@PLT
  movl  $0, %eax
  addq  $8, %rsp
  .cfi_def_cfa_offset 8
  ret

honey the codewitch wrote:

The thing is, all the documentation you've pointed me to suggests it should be doing the same thing in both cases.

• The rules of default argument promotion.
• The rules of passing arguments to variadic functions.

printf("%c\n",65);

printf("%c\n",foo<-1>::test());

push    rbp
mov     rbp, rsp
sub     rsp, 16
mov     DWORD PTR [rbp-4], edi
mov     QWORD PTR [rbp-16], rsi
mov     eax, 65 ; ***
movsx   eax, al ; ***
mov     edi, eax ;***
call    putchar
mov     edi, 65  ;***
call    putchar
mov     eax, 0
leave
ret

honey the codewitch wrote:

#pragma GCC optimize("Os")

It fixes it

honey the codewitch wrote:

I wish I could actually check my production code, but it relies on the Arduino framework, and I can't run that at godbolt. I've tried disassembler extensions in VSCode but none work with platformIO because it makes its own CMake/ninja scripts for everything on the fly.