qiongsiwu wrote:
I realized one problem during testing IRPGO (thanks again for the suggestion
@minglotus-6 !).
A functions control flow may change between `-fprofile-generate` and
`-fprofile-use` when we make use of definitions in the new header. For example,
one may have the following code:
```c
void main() {
...
if (__llvm_profile_dump())
return error;
cleanup();
}
```
During `-fprofile-generate`, `__llvm_profile_dump` is a declared name and
main's control flow includes a branch to `return error;`. During
`-fprofile-use`, `__llvm_profile_dump()` is replaced by `(0)` and the frontend
eliminates the `if` statement and the branch to `return error`. Such control
flow change can lead to PGO warnings (hash mismatch).
I think it may be OK to keep the PR this way because the new macros can
potentially cause control flow changes directly as well. The documentation is
updated
(https://github.com/llvm/llvm-project/pull/76471/files#diff-7389be311daf0b9b476c876bef04245fa3c0ad9337ce865682174bd77d53b648R2908)
to advise against using these APIs in a program's hot regions and warn about
possible impact on control flow.
Do you all think this is reasonable?
https://github.com/llvm/llvm-project/pull/76471
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