https://gcc.gnu.org/bugzilla/show_bug.cgi?id=125865
Bug ID: 125865
Summary: Unnecessary branches when expanding memset
Product: gcc
Version: 16.1.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: hjl.tools at gmail dot com
Target Milestone: ---
Target: x86-64
[hjl@gnu-zen4-1 pr125856]$ cat z.c
void
bounded_copy (char *dst, int c, __SIZE_TYPE__ n)
{
if (n <= 15)
__builtin_memset(dst, c, n);
}
[hjl@gnu-zen4-1 pr125856]$ gcc -S -O2 z.c
[hjl@gnu-zen4-1 pr125856]$ cat z.s
.file "z.c"
.text
.p2align 4
.globl bounded_copy
.type bounded_copy, @function
bounded_copy:
.LFB0:
.cfi_startproc
cmpq $15, %rdx
jbe .L17
.L1:
ret
.p2align 4,,10
.p2align 3
.L17:
movabsq $72340172838076673, %rax
movzbl %sil, %esi
imulq %rax, %rsi
movq %rsi, %xmm0
punpcklqdq %xmm0, %xmm0
cmpl $64, %edx
jnb .L3 <<<<<<<< Always false
testb $32, %dl
jne .L18 <<<<<<<< Always false
testb $16, %dl
jne .L19 <<<<<<<< Always false.
testb $8, %dl
jne .L20
testb $4, %dl
jne .L21
testl %edx, %edx
je .L1
movb %sil, (%rdi)
testb $2, %dl
je .L1
movl %edx, %edx
movw %si, -2(%rdi,%rdx)
ret
.p2align 4,,10
.p2align 3
.L3:
movl %edx, %eax
subl $1, %edx
movups %xmm0, -64(%rdi,%rax)
movups %xmm0, -48(%rdi,%rax)
movups %xmm0, -32(%rdi,%rax)
movups %xmm0, -16(%rdi,%rax)
cmpl $64, %edx
jb .L1
andl $-64, %edx
xorl %eax, %eax
.L10:
movl %eax, %ecx
addl $64, %eax
movups %xmm0, (%rdi,%rcx)
movups %xmm0, 16(%rdi,%rcx)
movups %xmm0, 32(%rdi,%rcx)
movups %xmm0, 48(%rdi,%rcx)
cmpl %edx, %eax
jb .L10
ret
.p2align 4,,10
.p2align 3
.L18:
movl %edx, %edx
movups %xmm0, (%rdi)
movups %xmm0, 16(%rdi)
movups %xmm0, -32(%rdi,%rdx)
movups %xmm0, -16(%rdi,%rdx)
ret
.p2align 4,,10
.p2align 3
.L19:
movl %edx, %edx
movups %xmm0, (%rdi)
movups %xmm0, -16(%rdi,%rdx)
ret
.p2align 4,,10
.p2align 3
.L20:
movl %edx, %edx
movq %rsi, (%rdi)
movq %rsi, -8(%rdi,%rdx)
ret
.p2align 4,,10
.p2align 3
.L21:
movl %edx, %edx
movl %esi, (%rdi)
movl %esi, -4(%rdi,%rdx)
ret
.cfi_endproc
.LFE0:
.size bounded_copy, .-bounded_copy
.ident "GCC: (GNU) 16.1.1 20260515 (Red Hat 16.1.1-2)"
.section .note.GNU-stack,"",@progbits
[hjl@gnu-zen4-1 pr125856]$
