[PATCH] D21811: [MBB] add a missing corner case in UpdateTerminator()

Haicheng Wu via llvm-commits llvm-commits at lists.llvm.org
Tue Jun 28 12:14:10 PDT 2016

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If the layout after the block placement is like this 

        JGE_1 <BB#9>, %EFLAGS<imp-use>
    Successors according to CFG: BB#9(0x80000000 / 0x80000000 = 100.00%)


where BB#8 ends with a conditional branch, but the next block is not its successor.  The conditional branch should be changed to unconditional branch in MachineBasicBlock::UpdateTerminator(), but this case is missing.  

In cases like above example, the results returned by AnalyzeBranch() are: TBB = branch target; FBB = nullptr; Cond = branch condition (not empty)

This corner cases happens if a block (e.g. BB#8) branches and fallthourghs into the same block (e.g. BB#9) before the block placement, and the block placement moves this successor (e.g. BB#9) somewhere else.  




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