[PATCH] D80572: [WebbAssembly] Fix a bug in removing unnecessary branches

[Heejin Ahn via Phabricator via llvm-commits]

aheejin created this revision.
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One of the things `removeUnnecessaryInstrs()` in CFGStackify does is to
remove an unnecessary unconditinal branch before an EH pad. When there
is an unconditional branch right before a catch instruction and it
branches to the end of `end_try` marker, we don't need the branch,
because it there is no exception, the control flow transfers to
that point anyway.

  bb0:
    try
      ...
      br bb2      <- Not necessary
  bb1:
    catch
      ...
  bb2:
    end

This applies when we have a conditional branch followed by an
unconditional one, in which case we should only remove the unconditional
branch. For example:

  bb0:
    try
      ...
      br_if someplace_else
      br bb2                 <- Not necessary
  bb1:
    catch
      ...
  bb2:
    end

But `TargetInstrInfo::removeBranch` we used removed all existing
branches when there are multiple ones. This patch fixes it by only
deleting the last (= unconditional) branch manually.

Also fixes some `preds` comments in the test file.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D80572

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

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