https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70055
--- Comment #8 from H.J. Lu <hjl.tools at gmail dot com> ---
Inlining mempcpy uses a callee-saved register:
hjl@gnu-6 tmp]$ cat m.c
extern char *src, *dst;
char *
foo (unsigned long i)
{
return __builtin_mempcpy (dst, src, i);
}
char *
bar (unsigned long i)
{
return __builtin_memcpy (dst, src, i) + i;
}
[hjl@gnu-6 tmp]$ gcc -S -O2 m.c
[hjl@gnu-6 tmp]$ cat m.s
.file "m.c"
.section .text.unlikely,"ax",@progbits
.LCOLDB0:
.text
.LHOTB0:
.p2align 4,,15
.globl foo
.type foo, @function
foo:
.LFB0:
.cfi_startproc
movq %rdi, %rdx
movq src(%rip), %rsi
movq dst(%rip), %rdi
jmp mempcpy
.cfi_endproc
.LFE0:
.size foo, .-foo
.section .text.unlikely
.LCOLDE0:
.text
.LHOTE0:
.section .text.unlikely
.LCOLDB1:
.text
.LHOTB1:
.p2align 4,,15
.globl bar
.type bar, @function
bar:
.LFB1:
.cfi_startproc
pushq %rbx
.cfi_def_cfa_offset 16
.cfi_offset 3, -16
movq %rdi, %rdx
movq %rdi, %rbx
movq src(%rip), %rsi
movq dst(%rip), %rdi
call memcpy
addq %rbx, %rax
popq %rbx
.cfi_def_cfa_offset 8
ret
.cfi_endproc
.LFE1:
.size bar, .-bar
.section .text.unlikely
.LCOLDE1:
.text
.LHOTE1:
.ident "GCC: (GNU) 5.3.1 20160212 (Red Hat 5.3.1-4)"
.section .note.GNU-stack,"",@progbits
[hjl@gnu-6 tmp]$
Not inlining mempcpy is preferred.
