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7f2eff792a
can be used by both the new pass manager and the old. This removes it from any of the virtual mess of the pass interfaces and lets it derive cleanly from the DominatorTreeBase<> template. In turn, tons of boilerplate interface can be nuked and it turns into a very straightforward extension of the base DominatorTree interface. The old analysis pass is now a simple wrapper. The names and style of this split should match the split between CallGraph and CallGraphWrapperPass. All of the users of DominatorTree have been updated to match using many of the same tricks as with CallGraph. The goal is that the common type remains the resulting DominatorTree rather than the pass. This will make subsequent work toward the new pass manager significantly easier. Also in numerous places things became cleaner because I switched from re-running the pass (!!! mid way through some other passes run!!!) to directly recomputing the domtree. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@199104 91177308-0d34-0410-b5e6-96231b3b80d8
212 lines
7.1 KiB
C++
212 lines
7.1 KiB
C++
//===-- UnreachableBlockElim.cpp - Remove unreachable blocks for codegen --===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This pass is an extremely simple version of the SimplifyCFG pass. Its sole
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// job is to delete LLVM basic blocks that are not reachable from the entry
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// node. To do this, it performs a simple depth first traversal of the CFG,
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// then deletes any unvisited nodes.
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//
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// Note that this pass is really a hack. In particular, the instruction
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// selectors for various targets should just not generate code for unreachable
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// blocks. Until LLVM has a more systematic way of defining instruction
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// selectors, however, we cannot really expect them to handle additional
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// complexity.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/CodeGen/Passes.h"
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#include "llvm/ADT/DepthFirstIterator.h"
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#include "llvm/ADT/SmallPtrSet.h"
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#include "llvm/CodeGen/MachineDominators.h"
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#include "llvm/CodeGen/MachineFunctionPass.h"
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#include "llvm/CodeGen/MachineLoopInfo.h"
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#include "llvm/CodeGen/MachineModuleInfo.h"
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#include "llvm/CodeGen/MachineRegisterInfo.h"
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#include "llvm/IR/Constant.h"
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#include "llvm/IR/Dominators.h"
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#include "llvm/IR/Function.h"
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#include "llvm/IR/Instructions.h"
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#include "llvm/IR/Type.h"
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#include "llvm/Pass.h"
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#include "llvm/Support/CFG.h"
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#include "llvm/Target/TargetInstrInfo.h"
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using namespace llvm;
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namespace {
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class UnreachableBlockElim : public FunctionPass {
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virtual bool runOnFunction(Function &F);
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public:
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static char ID; // Pass identification, replacement for typeid
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UnreachableBlockElim() : FunctionPass(ID) {
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initializeUnreachableBlockElimPass(*PassRegistry::getPassRegistry());
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}
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virtual void getAnalysisUsage(AnalysisUsage &AU) const {
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AU.addPreserved<DominatorTreeWrapperPass>();
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}
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};
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}
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char UnreachableBlockElim::ID = 0;
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INITIALIZE_PASS(UnreachableBlockElim, "unreachableblockelim",
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"Remove unreachable blocks from the CFG", false, false)
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FunctionPass *llvm::createUnreachableBlockEliminationPass() {
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return new UnreachableBlockElim();
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}
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bool UnreachableBlockElim::runOnFunction(Function &F) {
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SmallPtrSet<BasicBlock*, 8> Reachable;
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// Mark all reachable blocks.
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for (df_ext_iterator<Function*, SmallPtrSet<BasicBlock*, 8> > I =
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df_ext_begin(&F, Reachable), E = df_ext_end(&F, Reachable); I != E; ++I)
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/* Mark all reachable blocks */;
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// Loop over all dead blocks, remembering them and deleting all instructions
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// in them.
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std::vector<BasicBlock*> DeadBlocks;
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for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I)
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if (!Reachable.count(I)) {
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BasicBlock *BB = I;
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DeadBlocks.push_back(BB);
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while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
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PN->replaceAllUsesWith(Constant::getNullValue(PN->getType()));
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BB->getInstList().pop_front();
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}
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for (succ_iterator SI = succ_begin(BB), E = succ_end(BB); SI != E; ++SI)
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(*SI)->removePredecessor(BB);
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BB->dropAllReferences();
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}
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// Actually remove the blocks now.
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for (unsigned i = 0, e = DeadBlocks.size(); i != e; ++i) {
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DeadBlocks[i]->eraseFromParent();
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}
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return DeadBlocks.size();
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}
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namespace {
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class UnreachableMachineBlockElim : public MachineFunctionPass {
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virtual bool runOnMachineFunction(MachineFunction &F);
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virtual void getAnalysisUsage(AnalysisUsage &AU) const;
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MachineModuleInfo *MMI;
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public:
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static char ID; // Pass identification, replacement for typeid
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UnreachableMachineBlockElim() : MachineFunctionPass(ID) {}
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};
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}
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char UnreachableMachineBlockElim::ID = 0;
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INITIALIZE_PASS(UnreachableMachineBlockElim, "unreachable-mbb-elimination",
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"Remove unreachable machine basic blocks", false, false)
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char &llvm::UnreachableMachineBlockElimID = UnreachableMachineBlockElim::ID;
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void UnreachableMachineBlockElim::getAnalysisUsage(AnalysisUsage &AU) const {
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AU.addPreserved<MachineLoopInfo>();
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AU.addPreserved<MachineDominatorTree>();
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MachineFunctionPass::getAnalysisUsage(AU);
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}
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bool UnreachableMachineBlockElim::runOnMachineFunction(MachineFunction &F) {
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SmallPtrSet<MachineBasicBlock*, 8> Reachable;
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bool ModifiedPHI = false;
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MMI = getAnalysisIfAvailable<MachineModuleInfo>();
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MachineDominatorTree *MDT = getAnalysisIfAvailable<MachineDominatorTree>();
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MachineLoopInfo *MLI = getAnalysisIfAvailable<MachineLoopInfo>();
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// Mark all reachable blocks.
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for (df_ext_iterator<MachineFunction*, SmallPtrSet<MachineBasicBlock*, 8> >
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I = df_ext_begin(&F, Reachable), E = df_ext_end(&F, Reachable);
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I != E; ++I)
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/* Mark all reachable blocks */;
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// Loop over all dead blocks, remembering them and deleting all instructions
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// in them.
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std::vector<MachineBasicBlock*> DeadBlocks;
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for (MachineFunction::iterator I = F.begin(), E = F.end(); I != E; ++I) {
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MachineBasicBlock *BB = I;
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// Test for deadness.
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if (!Reachable.count(BB)) {
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DeadBlocks.push_back(BB);
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// Update dominator and loop info.
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if (MLI) MLI->removeBlock(BB);
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if (MDT && MDT->getNode(BB)) MDT->eraseNode(BB);
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while (BB->succ_begin() != BB->succ_end()) {
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MachineBasicBlock* succ = *BB->succ_begin();
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MachineBasicBlock::iterator start = succ->begin();
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while (start != succ->end() && start->isPHI()) {
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for (unsigned i = start->getNumOperands() - 1; i >= 2; i-=2)
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if (start->getOperand(i).isMBB() &&
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start->getOperand(i).getMBB() == BB) {
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start->RemoveOperand(i);
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start->RemoveOperand(i-1);
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}
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start++;
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}
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BB->removeSuccessor(BB->succ_begin());
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}
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}
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}
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// Actually remove the blocks now.
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for (unsigned i = 0, e = DeadBlocks.size(); i != e; ++i)
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DeadBlocks[i]->eraseFromParent();
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// Cleanup PHI nodes.
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for (MachineFunction::iterator I = F.begin(), E = F.end(); I != E; ++I) {
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MachineBasicBlock *BB = I;
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// Prune unneeded PHI entries.
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SmallPtrSet<MachineBasicBlock*, 8> preds(BB->pred_begin(),
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BB->pred_end());
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MachineBasicBlock::iterator phi = BB->begin();
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while (phi != BB->end() && phi->isPHI()) {
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for (unsigned i = phi->getNumOperands() - 1; i >= 2; i-=2)
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if (!preds.count(phi->getOperand(i).getMBB())) {
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phi->RemoveOperand(i);
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phi->RemoveOperand(i-1);
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ModifiedPHI = true;
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}
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if (phi->getNumOperands() == 3) {
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unsigned Input = phi->getOperand(1).getReg();
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unsigned Output = phi->getOperand(0).getReg();
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MachineInstr* temp = phi;
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++phi;
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temp->eraseFromParent();
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ModifiedPHI = true;
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if (Input != Output) {
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MachineRegisterInfo &MRI = F.getRegInfo();
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MRI.constrainRegClass(Input, MRI.getRegClass(Output));
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MRI.replaceRegWith(Output, Input);
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}
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continue;
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}
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++phi;
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}
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}
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F.RenumberBlocks();
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return (DeadBlocks.size() || ModifiedPHI);
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}
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