[llvm-dev] How does one reduce a function CFG to its entry block?

[Anmol P. Paralkar via llvm-dev]

Hello,
 I wish to reduce a function CFG to its entry block. I wrote the following code using lib/IR/Function.cpp/Function::dropAllReferences() (from llvm-3.6) as reference:

 Function *F; // Suitably initialized. BasicBlock *FEntryBlock = &F->getEntryBlock(); FEntryBlock->getTerminator()->eraseFromParent(); FEntryBlock->removeFromParent(); for (Function::iterator I = F->begin(), E = F->end(); I != E; ++I)    I->dropAllReferences(); while (!F->getBasicBlockList().empty())   F->getBasicBlockList().begin()->eraseFromParent(); FEntryBlock->insertInto(F); // ...subsequent provision of a terminator, etc.
  
 This does have the desired effect, but since I have no prior experience modifying LLVM, I am not sure if this is safe/legitimate or if my approach is flawed.
 [ I am also able to achieve this by  substituting the original terminator to the entry block by a:   br i1 true, label %__RELEVANT, %__DISCARD_REST_OF_OLD_BODY 
   and have the code-gen prepare step eliminate the (made) unreachable rest of the old body   so that only the original entry block with an unconditional branch to other relevant code that   I add, remains; as intended. However, I want to not rely on the change happening further   downstream; I'd prefer that the intended transformation be self-contained. ]

  Kindly comment.

Thank you,Anmol P. Paralkar
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