PR for llvm/llvm-project#56301 #644
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… not empty Close llvm/llvm-project#56301 Close llvm/llvm-project#64151 See the summary and the discussion of https://reviews.llvm.org/D157070 to get the full context. As @rjmccall pointed out, the key point of the root cause is that currently we didn't implement the semantics for '@llvm.coro.save' well ("after the await-ready returns false, the coroutine is considered to be suspended ") well. Since the semantics implies that we (the compiler) shouldn't write the spills into the coroutine frame in the await_suspend. But now it is possible due to some combinations of the optimizations so the semantics are broken. And the inlining is the root optimization of such optimizations. So in this patch, we tried to add the `noinline` attribute to the await_suspend call. Also as an optimization, we don't add the `noinline` attribute to the await_suspend call if the awaiter is an empty class. This should be correct since the programmers can't access the local variables in await_suspend if the awaiter is empty. I think this is necessary for the performance since it is pretty common. Another potential optimization is: call @llvm.coro.await_suspend(ptr %awaiter, ptr %handle, ptr @awaitSuspendFn) Then it is much easier to perform the safety analysis in the middle end. If it is safe to inline the call to awaitSuspend, we can replace it in the CoroEarly pass. Otherwise we could replace it in the CoroSplit pass. Reviewed By: rjmccall Differential Revision: https://reviews.llvm.org/D157833
… regressions The fix we sent for llvm/llvm-project#56301 may bring performance regressions. But we didn't mention it in the ReleaseNotes so that users may get confused. e.g, llvm/llvm-project#64933. So this patch mentions the possible side effect and the potential solutions in llvm/llvm-project#64945 to avoid misunderstandings.
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@web-flow What do you think about merging this PR to the release branch? |
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I'd like to backport this patch since the issue had been reported several places and relatively severe (I admit it looks more severe than I think initially). |
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resolves llvm/llvm-project#56301