[PATCH] D141579: [PGO] incorrect classof in InstrProfIncrementInst

[ZhouKui via Phabricator via llvm-commits]

KuiChou added a comment.

In D141579#4047994 <https://reviews.llvm.org/D141579#4047994>, @ellis wrote:

> Ah, I see the `dyn_cast` you are talking about is here <https://github.com/llvm/llvm-project/blob/9f1bb307da6fec6fc8123bdec79ecec28fced874/llvm/lib/Transforms/Instrumentation/InstrProfiling.cpp#L548-L549>. I think this is only a problem if `InstrProfIncrementInstStep` is the only InstrProf instruction in a function **and** it has an `llvm.instrprof.value.profile` instruction, which explains why we didn't catch this bug for so long. In that case, the later call to `getOrCreateRegionCounters()` will be skipped and, according to the comment, this is required for value profiling. Is that what you observed? If so it should be easy to add a small test case, probably similar to `llvm/test/Instrumentation/InstrProfiling/early-exit.ll`, but this could be followed up in another patch. Thanks for fixing!

Yes. But even if `InstrProfIncrementInstStep` is the only InstrProf instruction in a function, `getOrCreateRegionCounters` will still be called through `InstrProfiling::run` -> `lowerIntrinsics` -> `lowerIncrement` -> `getCounterAddress` -> `getOrCreateRegionCounters`. So, to reproduce this problem, we should satisfy two conditions:

1. `InstrProfIncrementInstStep` is the only InstrProf instruction in a function **and** it has `InstrProfValueProfileInst` instruction
2. `InstrProfValueProfileInst` must be **in front of** `InstrProfIncrementInstStep` instruction

PGO will always generate an `InstrProfIncrementInst` instruction in the front of a function so normally, this bug cannot happen


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