clang-13 regression: -fsave-optimization-record is generating empty files

[sylvestre]

Bugzilla Link	51642
Version	trunk
OS	All
Blocks	#50580 #51489
CC	@LebedevRI,@serge-sans-paille,@tstellar

Extended Description

echo "
#define N 1536
float A[N][N];
float B[N][N];
float C[N][N];

void init_array()
{
int i, j;
for (i = 0; i < N; i++) {
for (j = 0; j < N; j++) {
A[i][j] = (1+(ij)%1024)/2.0;
B[i][j] = (1+(ij)%1024)/2.0;
}
}
}

int main()
{
int i, j, k;
double t_start, t_end;
init_array();
for (i = 0; i < N; i++) {
for (j = 0; j < N; j++) {
C[i][j] = 0;
for (k = 0; k < N; k++)
C[i][j] = C[i][j] + A[i][k] * B[k][j];
}
}
return 0;
}
" > foo.c
With clang-12:
$ clang-12 -S -fsave-optimization-record -emit-llvm foo.c -o matmul.s
$ ls -al matmul.opt.yaml
-rw-r--r-- 1 sylvestre sylvestre 535 27 août 09:53 matmul.opt.yaml

With clang-13:
$ clang-13 -S -fsave-optimization-record -emit-llvm foo.c -o matmul.s
$ ls -al matmul.opt.yaml
-rw-r--r-- 1 sylvestre sylvestre 0 27 août 09:54 matmul.opt.yaml

[sylvestre]

This is with rc1, I am trying to see if I can reproduce with rc2

[sylvestre]

Same with rc2

[serge-sans-paille]

I can reproduce on main branch, but I also note that in -O2, everything is fine.
The change seems to be that -O0 still implies (at least) an inlining pass (probably to handle always inline) and that doesn't appear in clang-13.

[tstellar]

mentioned in issue #51489

[tstellar]

The deadline for requesting fixes for the release has passed. This bug is being removed from the LLVM 13.0.1 release milestone. If you have a fix or think this bug is important enough to block the release, please explain why in a comment and add the bug back to the LLVM 13.0.1 release milestone.

[fhahn]

This is caused by the switch to the new pass manager I think. The only remark that gets emitted by -O0 for the example is from the AlwaysInliner: https://clang.godbolt.org/z/s6srTvP47

It looks like the new pass manager uses a different always-inline implementation, which presumably doesn't emit that remark?