[PATCH] D97677: [WebAssembly] Fix more ExceptionInfo grouping bugs

[Heejin Ahn via Phabricator via llvm-commits]

aheejin created this revision.
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This fixes two bugs in `WebAssemblyExceptionInfo` grouping, created by
D97247 <https://reviews.llvm.org/D97247>:

- In D97247 <https://reviews.llvm.org/D97247>, when fixing `ExceptionInfo` grouping by taking out the unwind destination' exception from the unwind src's exception, we just iterated the BBs in the function order, but this was incorrect; this changes it to dominator tree preorder. Please refer to the comments in the code for the reason and an example.

- After this subexception-taking-out fix, there still can be remaining BBs we have to take out. When Exception B is taken out of Exception A (because EHPad B is the unwind destination of EHPad A), there can still be BBs within Exception A that are reachable from Exception B, which also should be taken out. Please refer to the comments in the code for more detailed explanation on why this can happen. To make this possible, this splits `WebAssemblyException::addBlock` into two parts: adding to a set and adding to a vector. We need to iterate on BBs within a `WebAssemblyException` to fix this, so we add BBs to sets first. But we add BBs to vectors later after we fix all incorrectness because deleting BBs from vectors is expensive. I considered removing the vector from `WebAssemblyException`, but it was not easy because this class has to maintain a similar interface with `MachineLoop` to be wrapped into a single interface `SortRegion`, which is used in CFGSort.

Other misc. drive-by fixes:

- Make `WebAssemblyExceptionInfo` do not even run when wasm EH is not used or the function doesn't have any EH pads, not to waste time
- Add `LLVM_DEBUG` lines for easy debugging
- Fix `preds` comments in cfg-stackify-eh.ll
- Fix `__cxa_throw`'s signature in cfg-stackify-eh.ll

Fixes https://github.com/emscripten-core/emscripten/issues/13554.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D97677

Files:
  llvm/lib/Target/WebAssembly/WebAssemblyExceptionInfo.cpp
  llvm/lib/Target/WebAssembly/WebAssemblyExceptionInfo.h
  llvm/test/CodeGen/WebAssembly/cfg-stackify-eh.ll

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