https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96966
Bug ID: 96966
Summary: redundant memcpy not eliminated after pointer
subtraction
Product: gcc
Version: 11.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: msebor at gcc dot gnu.org
Target Milestone: ---
The second call to memcpy and mempcpy, respectively, is redundant in each of
the functions below and can be eliminated. GCC doesn't notice the redundancy
and emits both pairs of copies. Clang emits just one call to memcpy but it too
fails to eliminate the redundant call to mempcpy.
$ cat z.c && gcc -O2 -S -o /dev/stdout z.c
extern char a[32];
void f (const void *s)
{
char *p = (char*)__builtin_memcpy (a, s, 16) + 16;
__builtin_memcpy (p - 16, s, 16);
}
void g (const void *s)
{
char *p = (char*)__builtin_mempcpy (a, s, 16);
__builtin_mempcpy (p - 16, s, 16);
}
.file "z.c"
.text
.p2align 4
.globl f
.type f, @function
f:
.LFB0:
.cfi_startproc
movdqu (%rdi), %xmm0
movups %xmm0, a(%rip)
movdqu (%rdi), %xmm1
movups %xmm1, a(%rip)
ret
.cfi_endproc
.LFE0:
.size f, .-f
.p2align 4
.globl g
.type g, @function
g:
.LFB3:
.cfi_startproc
movdqu (%rdi), %xmm0
movups %xmm0, a(%rip)
movdqu (%rdi), %xmm1
movups %xmm1, a(%rip)
ret
.cfi_endproc
.LFE3:
.size g, .-g
.ident "GCC: (GNU) 11.0.0 20200902 (experimental)"
.section .note.GNU-stack,"",@progbits
