Rollup merge of #55167 - nnethercote:is_missing_ctors_empty, r=varkor

Add a "cheap" mode for `compute_missing_ctors`.

`compute_missing_ctors` produces a vector. It is called a lot, but the
vector is almost always only checked for emptiness.

This commit introduces a specialized variant of `compute_missing_ctors`
(called `is_missing_ctors_empty`) that determines if the resulting set
would be empty, and changes the callsite so that `compute_missing_ctors`
is only called in the rare cases where it is needed. The code
duplication is unfortunate but I can't see a better way to do it.

This change reduces instruction counts for several benchmarks up to 2%.

r? @varkor

0 files changed, 0 insertions, 0 deletions