[all-commits] [llvm/llvm-project] 37f2f4: [DebugInfo][RemoveDIs] Handle a debug-info splicin...

[Jeremy Morse via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 37f2f48c8f43b2b98869a6e5f009d3d2471ecdaf
      https://github.com/llvm/llvm-project/commit/37f2f48c8f43b2b98869a6e5f009d3d2471ecdaf
  Author: Jeremy Morse <jeremy.morse at sony.com>
  Date:   2023-12-01 (Fri, 01 Dec 2023)

  Changed paths:
    M llvm/include/llvm/IR/BasicBlock.h
    M llvm/include/llvm/IR/DebugProgramInstruction.h
    M llvm/lib/IR/BasicBlock.cpp
    M llvm/unittests/IR/BasicBlockDbgInfoTest.cpp

  Log Message:
  -----------
  [DebugInfo][RemoveDIs] Handle a debug-info splicing corner case (#73810)

A large amount of complexity when it comes to shuffling DPValue objects
around is pushed into BasicBlock::spliceDebugInfo, and it gets
comprehensive testing there via the unit tests. It turns out that there's a
corner case though: splicing instructions and debug-info to the end()
iterator requires blocks of DPValues to be concatenated, but the DPValues
don't behave normally as they're dangling at the end of a block. While this
splicing-to-an-empty-block case is rare, and it's even rarer for it to
contain debug-info, it does happen occasionally.

Fix this by wrapping spliceDebugInfo with an outer layer that removes any
dangling DPValues in the destination block -- that way the main splicing
function (renamed to spliceDebugInfoImpl) doesn't need to worry about that
scenario. See the diagram in the added function for more info.