[PATCH] D92200: Deal with issue=>SplitEdge(BB, Succ, ...…

[Bangtian Liu via Phabricator via llvm-commits]

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This PR implements the function splitBasicBlockBefore to address an issue
that occurred during SplitEdge(BB, Succ, ...), inside splitBlockBefore.
The issue occurs in SplitEdge when the Succ has a single predecessor
 and the edge between the BB and Succ is not critical. This produces
the result ‘BB->Succ->New’. The new function splitBasicBlockBefore
was added to splitBlockBefore to handle the issue and now produces
the correct result ‘BB->New->Succ’.

Below is an example of splitting the block bb1 at its first instruction.

  /// Original IR
  bb0:
  	br bb1
  bb1:
          %0 = mul i32 1, 2
  	br bb2
  bb2:



  /// IR after splitEdge(bb0, bb1) using splitBasicBlock
  bb0:
  	br bb1
  bb1:
  	br bb1.split
  bb1.split:
          %0 = mul i32 1, 2
  	br bb2
  bb2:



  /// IR after splitEdge(bb0, bb1) using splitBasicBlockBefore
  bb0:
  	br bb1.split
  bb1.split
  	br bb1
  bb1:
          %0 = mul i32 1, 2
  	br bb2
  bb2:


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D92200

Files:
  llvm/include/llvm/IR/BasicBlock.h
  llvm/include/llvm/Transforms/Utils/BasicBlockUtils.h
  llvm/lib/IR/BasicBlock.cpp
  llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
  llvm/unittests/Transforms/Utils/BasicBlockUtilsTest.cpp

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