[all-commits] [llvm/llvm-project] 4a5811: [WebAssembly] Fix more ExceptionInfo grouping bugs

[Heejin Ahn via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 4a58116b7e5e1439c5fefdf59a89fc4f1d42875c
      https://github.com/llvm/llvm-project/commit/4a58116b7e5e1439c5fefdf59a89fc4f1d42875c
  Author: Heejin Ahn <aheejin at gmail.com>
  Date:   2021-03-02 (Tue, 02 Mar 2021)

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

  Log Message:
  -----------
  [WebAssembly] Fix more ExceptionInfo grouping bugs

This fixes two bugs in `WebAssemblyExceptionInfo` grouping, created by
D97247. These two bugs are not easy to split into two different CLs,
because tests that fail for one also tend to fail for the other.

- In 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.

Reviewed By: dschuff, tlively

Differential Revision: https://reviews.llvm.org/D97677