On 12/28/2025 7:03 PM, Sebastian Huber wrote:
I used this test case to double check that the shifting is now correct:
int a(void);
int b(void);
int c(int);
int f(int *i)
{
if (c(i[0]) || c(i[1]) || c(i[2]) || c(i[3]) || c(i[4]) ||
c(i[5]) || c(i[6]) || c(i[7]) || c(i[8]) || c(i[9]) ||
c(i[10]) || c(i[11]) || c(i[12]) || c(i[13]) || c(i[14]) ||
c(i[15]) || c(i[16]) || c(i[17]) || c(i[18]) || c(i[19]) ||
c(i[20]) || c(i[21]) || c(i[22]) || c(i[23]) || c(i[24]) ||
c(i[25]) || c(i[26]) || c(i[27]) || c(i[28]) || c(i[29]) ||
c(i[30]) || c(i[31]) || c(i[32]) || c(i[33]) || c(i[34]) ||
c(i[35]) || c(i[36]) || c(i[37]) || c(i[38]) || c(i[39])) {
return a();
} else {
return b();
}
}
Interestingly, GCC now reuses the "amoor.w zero,zero" operations (see "j .L46").
Right. That's not a huge surprise to me. If we look at the gimple we see:
;; basic block 3, loop depth 0
;; pred: 2
__atomic_fetch_or_4 (&__gcov8.f[0], 1, 0);
__atomic_fetch_or_4 (&MEM <long long int> [(void *)&__gcov8.f + 4B],
0, 0);
__atomic_fetch_or_4 (&__gcov8.f[1], 0, 0);
__atomic_fetch_or_4 (&MEM <long long int> [(void *)&__gcov8.f +
12B], 0, 0);
_8 = a (i_3(D)); [tail call]
goto <bb 5>; [100.00%]
;; succ: 5
;; basic block 4, loop depth 0
;; pred: 2
__atomic_fetch_or_4 (&__gcov8.f[0], 0, 0);
__atomic_fetch_or_4 (&MEM <long long int> [(void *)&__gcov8.f + 4B],
0, 0);
__atomic_fetch_or_4 (&__gcov8.f[1], 1, 0);
__atomic_fetch_or_4 (&MEM <long long int> [(void *)&__gcov8.f +
12B], 0, 0);
_6 = b (0); [tail call]
So to improve the code you need to recognize the atomic_fetch_or_4 where
the object is IOR'd with the constant 0 as a nop and remove those
statements (or not emit them to begin with). In general our optimizers
don't do a whole lot with atomics right now.
I think your change is missing a check somewhere. When I compile your
test I initially get "target does not support atomic profile update,
single mode is selected", but then it still does the atomic path.
Before your patch is just used the non-atomic updates. So it appears
something isn't quite right yet.
jeff
