[all-commits] [llvm/llvm-project] 2a814c: Ensure SplitEdge to return the new block between t...

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  Branch: refs/heads/master
  Home:   https://github.com/llvm/llvm-project
  Commit: 2a814cd9e1e8493c6606712d55f9ffdb58396481
      https://github.com/llvm/llvm-project/commit/2a814cd9e1e8493c6606712d55f9ffdb58396481
  Author: Whitney Tsang <whitneyt at ca.ibm.com>
  Date:   2020-12-18 (Fri, 18 Dec 2020)

  Changed paths:
    M llvm/include/llvm/IR/BasicBlock.h
    M llvm/include/llvm/Transforms/Utils/BasicBlockUtils.h
    M llvm/lib/IR/BasicBlock.cpp
    M llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
    M llvm/test/CodeGen/AMDGPU/call-constexpr.ll
    M llvm/test/Transforms/LoopUnswitch/2011-11-18-SimpleSwitch.ll
    M llvm/unittests/Transforms/Utils/BasicBlockUtilsTest.cpp

  Log Message:
  -----------
  Ensure SplitEdge to return the new block between the two given blocks

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:

Differential Revision: https://reviews.llvm.org/D92200