nikic added a comment.
I gave D77952 <https://reviews.llvm.org/D77952> a try (on top of this one), but
didn't see a significant improvement from that change.
Looking at the callgrind output for compilation of a **small** file, I see 52M
total instructions, 4 calls to TLII initialization, where addition of the
vector functions takes up the majority of the time, at 0.7M. Most of the cost
is in the sorting. 2 of the initialization calls are default-constructed TLII
without target triple, which seems suspect to me (are we not adding TLI early
enough, and something pulls it in via analysis dependency?)
So for small files, just registering the vector functions does make up a
non-trivial fraction of time, and lazy initialization might make sense. This
isn't the whole truth though: While the largest regressions are indeed on small
files, there are also quite a few > 1% regressions on very large files.
For a mid-size file with ~6000M instructions retried, the main difference I see
is `TargetLibraryAnalysis::run()` going up from 82M to 126M, with the cost
coming from the extra `getFnAttribute("veclib")` call in the TargetLibraryInfo
constructor. Fetching attributes is surprisingly expensive, as it performs an
iteration over all attributes internally. As this code is iterating over all
attributes anyway in order to handle `no-builtin-*`, it might make sense to
move the checks for `"veclib"` and `"no-builtins"` into that loop as well,
which should make them essentially free.
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D77632/new/
https://reviews.llvm.org/D77632
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