[Bug tree-optimization/86010] [7/8 Regression] redundant memset with smaller size not eliminated

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86010

Martin Sebor <msebor at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |missed-optimization

--- Comment #1 from Martin Sebor <msebor at gcc dot gnu.org> ---
The difference is better seen in the assembly output for the two functions:

g:
        .cfi_startproc
        subq    $24, %rsp
        .cfi_def_cfa_offset 32
        movq    $0, 8(%rsp)
        leaq    8(%rsp), %rdi
        call    f
        addq    $24, %rsp
        .cfi_def_cfa_offset 8
        ret
        .cfi_endproc

h:
        .cfi_startproc
        subq    $24, %rsp
        .cfi_def_cfa_offset 32
        xorl    %eax, %eax
        xorl    %edx, %edx
        leaq    8(%rsp), %rdi
        movw    %ax, 14(%rsp)
        movl    $0, 8(%rsp)
        movw    %dx, 12(%rsp)
        call    f
        addq    $24, %rsp
        .cfi_def_cfa_offset 8
        ret
        .cfi_endproc


Clang 6 emits the following:

g():
  push rax
  mov qword ptr [rsp], 0
  mov rdi, rsp
  call f(void*)
  pop rax
  ret

h():
  push rax
  mov qword ptr [rsp], 0
  mov rdi, rsp
  call f(void*)
  pop rax
  ret