[llvm-dev] LLVM Regions after SplitEdge

[Charitha Saumya via llvm-dev]

Hi,

I have the following CFG.
[image: Screenshot from 2020-10-20 22-24-45.png]
Regions for this CFG are.
[0] entry => if.end12
  [1] if.else => if.end
An optimization pass I am working on requires if.then block to be a LLVM
region. Therefore I used the SplitEdge function (in BasicBlockUtils) to
split the edge if.then -> if.end12. Now I have the following CFG,
[image: Screenshot from 2020-10-20 22-25-07.png]
However my regions are still,
[0] entry => if.end12
  [1] if.else => if.end

if.then=>if.then.split is not a region. Can someone explain why this is not
a LLVM region? It's a single entry single exit control flow. Why is it not
a region?


Also what is the correct way to recalculate LLVM regions after modifying
the controlflow?

Following approach gave me a  runtime error when run on the function after
splitting the  if.then -> if.end12 ,

    RegionInfo &RI = getAnalysis<RegionInfoPass>().getRegionInfo();
    DominatorTree &DT =
getAnalysis<DominatorTreeWrapperPass>().getDomTree();
    DominanceFrontier &DF =
getAnalysis<DominanceFrontierWrapperPass>().getDominanceFrontier();
    PostDominatorTree &PDT =
getAnalysis<PostDominatorTreeWrapperPass>().getPostDomTree();

     DT.recalculate(F);
     PDT.recalculate(F);
     RI.recalculate(F, &DT, &PDT, &DF);

Runtime error,

Stack dump:
0. Program arguments: /home/charitha/workspace/llvm_install/bin/opt -load
/home/charitha/workspace/llvm-project/build/lib/LLVMCFMerger.so -cfmerger
-view-cfg-only
1. Running pass 'Function Pass Manager' on module '<stdin>'.
2. Running pass 'Merge similar control flow for divergence reduction' on
function '@foo'
 #0 0x000056094798307a llvm::sys::PrintStackTrace(llvm::raw_ostream&)
(/home/charitha/workspace/llvm_install/bin/opt+0x299407a)
 #1 0x0000560947980df4 llvm::sys::RunSignalHandlers()
(/home/charitha/workspace/llvm_install/bin/opt+0x2991df4)
 #2 0x0000560947980f43 SignalHandler(int)
(/home/charitha/workspace/llvm_install/bin/opt+0x2991f43)
 #3 0x00007fc487be33c0 __restore_rt
(/lib/x86_64-linux-gnu/libpthread.so.0+0x153c0)
 #4 0x0000560946b7a6a0
llvm::RegionInfoBase<llvm::RegionTraits<llvm::Function>
>::isRegion(llvm::BasicBlock*, llvm::BasicBlock*) const

Thanks,
Charitha
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