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697954c15d
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@1503 91177308-0d34-0410-b5e6-96231b3b80d8
71 lines
2.8 KiB
C++
71 lines
2.8 KiB
C++
//===- SimplifyCFG.cpp - CFG Simplification Routines -------------*- C++ -*--=//
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//
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// This file provides several routines that are useful for simplifying CFGs in
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// various ways...
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Analysis/SimplifyCFG.h"
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#include "llvm/BasicBlock.h"
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#include "llvm/Method.h"
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#include "llvm/iTerminators.h"
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#include "llvm/iPHINode.h"
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#include "llvm/Type.h"
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using std::vector;
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// UnifyAllExitNodes - Unify all exit nodes of the CFG by creating a new
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// BasicBlock, and converting all returns to unconditional branches to this
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// new basic block. The singular exit node is returned.
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//
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// If there are no return stmts in the Method, a null pointer is returned.
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//
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BasicBlock *cfg::UnifyAllExitNodes(Method *M) {
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vector<BasicBlock*> ReturningBlocks;
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// Loop over all of the blocks in a method, tracking all of the blocks that
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// return.
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//
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for(Method::iterator I = M->begin(), E = M->end(); I != E; ++I)
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if ((*I)->getTerminator()->getOpcode() == Instruction::Ret)
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ReturningBlocks.push_back(*I);
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if (ReturningBlocks.size() == 0)
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return 0; // No blocks return
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else if (ReturningBlocks.size() == 1)
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return ReturningBlocks.front(); // Already has a single return block
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// Otherwise, we need to insert a new basic block into the method, add a PHI
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// node (if the function returns a value), and convert all of the return
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// instructions into unconditional branches.
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//
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BasicBlock *NewRetBlock = new BasicBlock("", M);
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if (M->getReturnType() != Type::VoidTy) {
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// If the method doesn't return void... add a PHI node to the block...
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PHINode *PN = new PHINode(M->getReturnType());
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NewRetBlock->getInstList().push_back(PN);
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// Add an incoming element to the PHI node for every return instruction that
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// is merging into this new block...
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for (vector<BasicBlock*>::iterator I = ReturningBlocks.begin(),
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E = ReturningBlocks.end(); I != E; ++I)
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PN->addIncoming((*I)->getTerminator()->getOperand(0), *I);
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// Add a return instruction to return the result of the PHI node...
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NewRetBlock->getInstList().push_back(new ReturnInst(PN));
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} else {
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// If it returns void, just add a return void instruction to the block
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NewRetBlock->getInstList().push_back(new ReturnInst());
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}
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// Loop over all of the blocks, replacing the return instruction with an
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// unconditional branch.
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//
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for (vector<BasicBlock*>::iterator I = ReturningBlocks.begin(),
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E = ReturningBlocks.end(); I != E; ++I) {
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delete (*I)->getInstList().pop_back(); // Remove the return insn
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(*I)->getInstList().push_back(new BranchInst(NewRetBlock));
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}
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return NewRetBlock;
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}
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