https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114991
Bug ID: 114991
Summary: [14/15 Regression] AArch64: LDP pass does not handle
some structure copies
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: wilco at gcc dot gnu.org
Target Milestone: ---
The following example no longer emits LDP/STP since GCC14:
#include <string.h>
typedef struct { int arr[20]; } S;
void g (S *);
void h (S);
void f(int x)
{
S s;
g (&s);
h (s);
}
f:
stp x29, x30, [sp, -176]!
add x1, sp, 96
mov x29, sp
add x0, sp, 16
ldp q29, q31, [x1]
ldr q30, [x1, 32]
str q29, [sp, 16]
ldr q29, [x1, 48]
str q31, [x0, 16]
ldr q31, [x1, 64]
stp q30, q29, [x0, 32]
str q31, [x0, 64]
bl h
ldp x29, x30, [sp], 176
ret
The expansions for memcpy/move/memset no longer emit LDP directly in RTL and
now rely on the new LDP pass. Stack based loads/stores seem to confuse its
alias checks and it gives up.
Using -fno-schedule-insns fixes this example, but not all cases.
