https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103197
Bug ID: 103197
Summary: ppc inline expansion of memcpy/memmove should not use
lxsibzx/stxsibx for a single byte
Product: gcc
Version: 10.3.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: acsawdey at gcc dot gnu.org
Target Milestone: ---
This got broken sometime in gcc 10 timeframe. For this test case:
#include <string.h>
void m(char *a, char *b)
{
memcpy(a,b,9);
}
AT13 (gcc 9.3.1) produces:
m:
.LFB0:
.cfi_startproc
ld 10,0(4)
lbz 9,8(4)
std 10,0(3)
stb 9,8(3)
blr
.long 0
.byte 0,0,0,0,0,0,0,0
.cfi_endproc
which is the expected code to copy 9 bytes.
AT14 (gcc 10.3.1), gcc 11, and current trunk all produce:
m:
.LFB0:
.cfi_startproc
addi 10,4,8
ld 9,0(4)
lxsibzx 0,0,10
std 9,0(3)
addi 9,3,8
stxsibx 0,0,9
blr
.long 0
.byte 0,0,0,0,0,0,0,0
.cfi_endproc
which is really bad, mixing gpr and vsx. The inline expansion code in
expand_block_move() does not attempt to generate vsx code at all unless the
size is at least 16 bytes.
