https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97421
Bug ID: 97421
Summary: [10/11 Regression] aarch64: Wrong code with -O2
-fmodulo-sched since r10-1318-ga7e8a46
Product: gcc
Version: 11.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: acoplan at gcc dot gnu.org
Target Milestone: ---
AArch64 GCC miscompiles the following testcase:
int a, b, d, e;
int *volatile c = &a;
__attribute__((noinline))
void f(void)
{
for (int g = 2; g >= 0; g--) {
d = 0;
for (b = 0; b <= 2; b++)
;
e = *c;
}
}
int main(void)
{
f();
if (b != 3)
__builtin_abort();
}
with -O2 -fmodulo-sched since
r10-1318-ga7e8a463cd1dbaccf6e7c4fa888768fcd257a30f. Removing -fmodulo-sched,
the testcase is compiled correctly (tested at -O0 through -O3).
Here is the generated code (current trunk) for f at -O2:
f:
mov w1, 3
adrp x0, .LANCHOR0
adrp x3, .LANCHOR1
mov w4, w1
add x0, x0, :lo12:.LANCHOR0 // x0 <- &d
add x3, x3, :lo12:.LANCHOR1 // x3 <- &c
.L2:
ldr x2, [x3] // x2 <- c
stp wzr, w4, [x0] // d = 0, b = 3
subs w1, w1, #1
ldr w2, [x2] // w2 <- *c
str w2, [x0, 8] // e <- w2
bne .L2
ret
and the code for f with -O2 -fmodulo-sched:
f:
mov w1, 2
adrp x0, .LANCHOR0
mov w4, w1
add x0, x0, :lo12:.LANCHOR0
adrp x3, .LANCHOR1
add x3, x3, :lo12:.LANCHOR1
ldr x2, [x3] // x2 <- c
str w1, [x0, 4] // b = 2
.L2:
str wzr, [x0] // d = 0
ldr w2, [x2] // w2 <- *c
subs w1, w1, #1
str w2, [x0, 8] // e <- w2
ldr x2, [x3] // x2 <- c
str w4, [x0, 4] // b = 2
bne .L2
ldr w2, [x2] // w2 <- *c
str w2, [x0, 8] // e <- w2
ret
In the latter case we end up with b = 2 and make the call to __builtin_abort().
