forked from OSchip/llvm-project
This pass has never worked correctly. Remove.
llvm-svn: 25349
This commit is contained in:
Chris Lattner
parent
93f72dce59
commit
0de2c7d3d8
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@ -1,629 +0,0 @@
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//===- PRE.cpp - Partial Redundancy Elimination ---------------------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file was developed by the LLVM research group and is distributed under
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// the University of Illinois Open Source License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file implements the well-known Partial Redundancy Elimination
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// optimization, using an SSA formulation based on e-paths. See this paper for
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// more information:
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//
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// E-path_PRE: partial redundancy elimination made easy
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// By: Dhananjay M. Dhamdhere In: ACM SIGPLAN Notices. Vol 37, #8, 2002
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// http://doi.acm.org/10.1145/596992.597004
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//
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// This file actually implements a sparse version of the algorithm, using SSA
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// and CFG properties instead of bit-vectors.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Pass.h"
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#include "llvm/Function.h"
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#include "llvm/Type.h"
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#include "llvm/Instructions.h"
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#include "llvm/Support/CFG.h"
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#include "llvm/Analysis/Dominators.h"
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#include "llvm/Analysis/PostDominators.h"
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#include "llvm/Analysis/ValueNumbering.h"
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#include "llvm/Transforms/Scalar.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/ADT/DepthFirstIterator.h"
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#include "llvm/ADT/PostOrderIterator.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/ADT/hash_set"
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#include "llvm/ADT/hash_map"
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using namespace llvm;
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namespace {
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Statistic<> NumExprsEliminated("pre", "Number of expressions constantified");
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Statistic<> NumRedundant ("pre", "Number of redundant exprs eliminated");
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Statistic<> NumInserted ("pre", "Number of expressions inserted");
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struct PRE : public FunctionPass {
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virtual void getAnalysisUsage(AnalysisUsage &AU) const {
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AU.addRequiredID(BreakCriticalEdgesID); // No critical edges for now!
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AU.addRequired<PostDominatorTree>();
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AU.addRequired<PostDominanceFrontier>();
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AU.addRequired<DominatorSet>();
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AU.addRequired<DominatorTree>();
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AU.addRequired<DominanceFrontier>();
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AU.addRequired<ValueNumbering>();
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}
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virtual bool runOnFunction(Function &F);
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private:
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// Block information - Map basic blocks in a function back and forth to
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// unsigned integers.
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std::vector<BasicBlock*> BlockMapping;
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hash_map<BasicBlock*, unsigned> BlockNumbering;
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// ProcessedExpressions - Keep track of which expressions have already been
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// processed.
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hash_set<Instruction*> ProcessedExpressions;
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// Provide access to the various analyses used...
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DominatorSet *DS;
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DominatorTree *DT; PostDominatorTree *PDT;
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DominanceFrontier *DF; PostDominanceFrontier *PDF;
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ValueNumbering *VN;
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// AvailableBlocks - Contain a mapping of blocks with available expression
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// values to the expression value itself. This can be used as an efficient
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// way to find out if the expression is available in the block, and if so,
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// which version to use. This map is only used while processing a single
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// expression.
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//
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typedef hash_map<BasicBlock*, Instruction*> AvailableBlocksTy;
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AvailableBlocksTy AvailableBlocks;
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bool ProcessBlock(BasicBlock *BB);
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// Anticipatibility calculation...
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void MarkPostDominatingBlocksAnticipatible(PostDominatorTree::Node *N,
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std::vector<char> &AntBlocks,
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Instruction *Occurrence);
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void CalculateAnticipatiblityForOccurrence(unsigned BlockNo,
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std::vector<char> &AntBlocks,
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Instruction *Occurrence);
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void CalculateAnticipatibleBlocks(const std::map<unsigned, Instruction*> &D,
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std::vector<char> &AnticipatibleBlocks);
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// PRE for an expression
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void MarkOccurrenceAvailableInAllDominatedBlocks(Instruction *Occurrence,
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BasicBlock *StartBlock);
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void ReplaceDominatedAvailableOccurrencesWith(Instruction *NewOcc,
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DominatorTree::Node *N);
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bool ProcessExpression(Instruction *I);
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};
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RegisterOpt<PRE> Z("pre", "Partial Redundancy Elimination");
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}
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FunctionPass* llvm::createPREPass() { return new PRE(); }
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bool PRE::runOnFunction(Function &F) {
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VN = &getAnalysis<ValueNumbering>();
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DS = &getAnalysis<DominatorSet>();
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DT = &getAnalysis<DominatorTree>();
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DF = &getAnalysis<DominanceFrontier>();
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PDT = &getAnalysis<PostDominatorTree>();
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PDF = &getAnalysis<PostDominanceFrontier>();
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DEBUG(std::cerr << "\n*** Running PRE on func '" << F.getName() << "'...\n");
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// Number the basic blocks based on a reverse post-order traversal of the CFG
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// so that all predecessors of a block (ignoring back edges) are visited
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// before a block is visited.
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//
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BlockMapping.reserve(F.size());
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{
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ReversePostOrderTraversal<Function*> RPOT(&F);
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DEBUG(std::cerr << "Block order: ");
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for (ReversePostOrderTraversal<Function*>::rpo_iterator I = RPOT.begin(),
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E = RPOT.end(); I != E; ++I) {
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// Keep track of mapping...
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BasicBlock *BB = *I;
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BlockNumbering.insert(std::make_pair(BB, BlockMapping.size()));
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BlockMapping.push_back(BB);
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DEBUG(std::cerr << BB->getName() << " ");
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}
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DEBUG(std::cerr << "\n");
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}
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// Traverse the current function depth-first in dominator-tree order. This
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// ensures that we see all definitions before their uses (except for PHI
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// nodes), allowing us to hoist dependent expressions correctly.
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bool Changed = false;
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for (unsigned i = 0, e = BlockMapping.size(); i != e; ++i)
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Changed |= ProcessBlock(BlockMapping[i]);
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// Free memory
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BlockMapping.clear();
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BlockNumbering.clear();
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ProcessedExpressions.clear();
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return Changed;
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}
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// ProcessBlock - Process any expressions first seen in this block...
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//
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bool PRE::ProcessBlock(BasicBlock *BB) {
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bool Changed = false;
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// DISABLED: This pass invalidates iterators and then uses them.
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return false;
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// PRE expressions first defined in this block...
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for (BasicBlock::iterator I = BB->begin(); I != BB->end(); )
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if (ProcessExpression(I++))
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Changed = true;
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return Changed;
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}
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void PRE::MarkPostDominatingBlocksAnticipatible(PostDominatorTree::Node *N,
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std::vector<char> &AntBlocks,
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Instruction *Occurrence) {
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unsigned BlockNo = BlockNumbering[N->getBlock()];
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if (AntBlocks[BlockNo]) return; // Already known to be anticipatible??
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// Check to see if any of the operands are defined in this block, if so, the
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// entry of this block does not anticipate the expression. This computes
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// "transparency".
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for (unsigned i = 0, e = Occurrence->getNumOperands(); i != e; ++i)
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if (Instruction *I = dyn_cast<Instruction>(Occurrence->getOperand(i)))
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if (I->getParent() == N->getBlock()) // Operand is defined in this block!
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return;
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if (isa<LoadInst>(Occurrence))
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return; // FIXME: compute transparency for load instructions using AA
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// Insert block into AntBlocks list...
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AntBlocks[BlockNo] = true;
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for (PostDominatorTree::Node::iterator I = N->begin(), E = N->end(); I != E;
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++I)
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MarkPostDominatingBlocksAnticipatible(*I, AntBlocks, Occurrence);
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}
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void PRE::CalculateAnticipatiblityForOccurrence(unsigned BlockNo,
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std::vector<char> &AntBlocks,
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Instruction *Occurrence) {
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if (AntBlocks[BlockNo]) return; // Block already anticipatible!
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BasicBlock *BB = BlockMapping[BlockNo];
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// For each occurrence, mark all post-dominated blocks as anticipatible...
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MarkPostDominatingBlocksAnticipatible(PDT->getNode(BB), AntBlocks,
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Occurrence);
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// Next, mark any blocks in the post-dominance frontier as anticipatible iff
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// all successors are anticipatible.
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//
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PostDominanceFrontier::iterator PDFI = PDF->find(BB);
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if (PDFI != DF->end())
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for (std::set<BasicBlock*>::iterator DI = PDFI->second.begin();
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DI != PDFI->second.end(); ++DI) {
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BasicBlock *PDFBlock = *DI;
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bool AllSuccessorsAnticipatible = true;
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for (succ_iterator SI = succ_begin(PDFBlock), SE = succ_end(PDFBlock);
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SI != SE; ++SI)
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if (!AntBlocks[BlockNumbering[*SI]]) {
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AllSuccessorsAnticipatible = false;
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break;
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}
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if (AllSuccessorsAnticipatible)
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CalculateAnticipatiblityForOccurrence(BlockNumbering[PDFBlock],
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AntBlocks, Occurrence);
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}
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}
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void PRE::CalculateAnticipatibleBlocks(const std::map<unsigned,
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Instruction*> &Defs,
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std::vector<char> &AntBlocks) {
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// Initialize to zeros...
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AntBlocks.resize(BlockMapping.size());
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// Loop over all of the expressions...
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for (std::map<unsigned, Instruction*>::const_iterator I = Defs.begin(),
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E = Defs.end(); I != E; ++I)
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CalculateAnticipatiblityForOccurrence(I->first, AntBlocks, I->second);
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}
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/// MarkOccurrenceAvailableInAllDominatedBlocks - Add entries to AvailableBlocks
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/// for all nodes dominated by the occurrence to indicate that it is now the
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/// available occurrence to use in any of these blocks.
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///
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void PRE::MarkOccurrenceAvailableInAllDominatedBlocks(Instruction *Occurrence,
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BasicBlock *BB) {
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// FIXME: There are much more efficient ways to get the blocks dominated
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// by a block. Use them.
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//
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DominatorTree::Node *N = DT->getNode(Occurrence->getParent());
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for (df_iterator<DominatorTree::Node*> DI = df_begin(N), E = df_end(N);
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DI != E; ++DI)
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AvailableBlocks[(*DI)->getBlock()] = Occurrence;
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}
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/// ReplaceDominatedAvailableOccurrencesWith - This loops over the region
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/// dominated by N, replacing any available expressions with NewOcc.
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void PRE::ReplaceDominatedAvailableOccurrencesWith(Instruction *NewOcc,
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DominatorTree::Node *N) {
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BasicBlock *BB = N->getBlock();
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Instruction *&ExistingAvailableVal = AvailableBlocks[BB];
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// If there isn't a definition already active in this node, make this the new
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// active definition...
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if (ExistingAvailableVal == 0) {
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ExistingAvailableVal = NewOcc;
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for (DominatorTree::Node::iterator I = N->begin(), E = N->end(); I != E;++I)
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ReplaceDominatedAvailableOccurrencesWith(NewOcc, *I);
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} else {
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// If there is already an active definition in this block, replace it with
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// NewOcc, and force it into all dominated blocks.
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DEBUG(std::cerr << " Replacing dominated occ %"
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<< ExistingAvailableVal->getName() << " with %" << NewOcc->getName()
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<< "\n");
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assert(ExistingAvailableVal != NewOcc && "NewOcc already inserted??");
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ExistingAvailableVal->replaceAllUsesWith(NewOcc);
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++NumRedundant;
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assert(ExistingAvailableVal->getParent() == BB &&
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"OldOcc not defined in current block?");
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BB->getInstList().erase(ExistingAvailableVal);
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// Mark NewOCC as the Available expression in all blocks dominated by BB
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for (df_iterator<DominatorTree::Node*> DI = df_begin(N), E = df_end(N);
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DI != E; ++DI)
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AvailableBlocks[(*DI)->getBlock()] = NewOcc;
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}
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}
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/// ProcessExpression - Given an expression (instruction) process the
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/// instruction to remove any partial redundancies induced by equivalent
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/// computations. Note that we only need to PRE each expression once, so we
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/// keep track of whether an expression has been PRE'd already, and don't PRE an
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/// expression again. Expressions may be seen multiple times because process
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/// the entire equivalence class at once, which may leave expressions later in
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/// the control path.
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///
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bool PRE::ProcessExpression(Instruction *Expr) {
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if (Expr->mayWriteToMemory() || Expr->getType() == Type::VoidTy ||
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isa<PHINode>(Expr))
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return false; // Cannot move expression
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if (ProcessedExpressions.count(Expr)) return false; // Already processed.
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// Ok, this is the first time we have seen the expression. Build a set of
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// equivalent expressions using SSA def/use information. We consider
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// expressions to be equivalent if they are the same opcode and have
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// equivalent operands. As a special case for SSA, values produced by PHI
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// nodes are considered to be equivalent to all of their operands.
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//
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std::vector<Value*> Values;
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VN->getEqualNumberNodes(Expr, Values);
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#if 0
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// FIXME: This should handle PHI nodes correctly. To do this, we need to
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// consider expressions of the following form equivalent to this set of
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// expressions:
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//
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// If an operand is a PHI node, add any occurrences of the expression with the
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// PHI operand replaced with the PHI node operands. This is only valid if the
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// PHI operand occurrences exist in blocks post-dominated by the incoming edge
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// of the PHI node.
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#endif
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// We have to be careful to handle expression definitions which dominated by
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// other expressions. These can be directly eliminated in favor of their
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// dominating value. Keep track of which blocks contain definitions (the key)
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// and if a block contains a definition, which instruction it is.
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//
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std::map<unsigned, Instruction*> Definitions;
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Definitions.insert(std::make_pair(BlockNumbering[Expr->getParent()], Expr));
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bool Changed = false;
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// Look at all of the equal values. If any of the values is not an
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// instruction, replace all other expressions immediately with it (it must be
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// an argument or a constant or something). Otherwise, convert the list of
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// values into a list of expression (instruction) definitions ordering
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// according to their dominator tree ordering.
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//
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Value *NonInstValue = 0;
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for (unsigned i = 0, e = Values.size(); i != e; ++i)
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if (Instruction *I = dyn_cast<Instruction>(Values[i])) {
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Instruction *&BlockInst = Definitions[BlockNumbering[I->getParent()]];
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if (BlockInst && BlockInst != I) { // Eliminate direct redundancy
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if (DS->dominates(I, BlockInst)) { // I dom BlockInst
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BlockInst->replaceAllUsesWith(I);
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BlockInst->getParent()->getInstList().erase(BlockInst);
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} else { // BlockInst dom I
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I->replaceAllUsesWith(BlockInst);
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I->getParent()->getInstList().erase(I);
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I = BlockInst;
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}
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++NumRedundant;
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}
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BlockInst = I;
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} else {
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NonInstValue = Values[i];
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}
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std::vector<Value*>().swap(Values); // Done with the values list
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if (NonInstValue) {
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// This is the good, though unlikely, case where we find out that this
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// expression is equal to a constant or argument directly. We can replace
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// this and all of the other equivalent instructions with the value
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// directly.
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//
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for (std::map<unsigned, Instruction*>::iterator I = Definitions.begin(),
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E = Definitions.end(); I != E; ++I) {
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Instruction *Inst = I->second;
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// Replace the value with the specified non-instruction value.
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Inst->replaceAllUsesWith(NonInstValue); // Fixup any uses
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Inst->getParent()->getInstList().erase(Inst); // Erase the instruction
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}
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NumExprsEliminated += Definitions.size();
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return true; // Program modified!
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}
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// There are no expressions equal to this one. Exit early.
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assert(!Definitions.empty() && "no equal expressions??");
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#if 0
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if (Definitions.size() == 1) {
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ProcessedExpressions.insert(Definitions.begin()->second);
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return Changed;
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}
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#endif
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DEBUG(std::cerr << "\n====--- Expression: " << *Expr);
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const Type *ExprType = Expr->getType();
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// AnticipatibleBlocks - Blocks where the current expression is anticipatible.
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// This is logically std::vector<bool> but using 'char' for performance.
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std::vector<char> AnticipatibleBlocks;
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// Calculate all of the blocks which the current expression is anticipatible.
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CalculateAnticipatibleBlocks(Definitions, AnticipatibleBlocks);
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// Print out anticipatible blocks...
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DEBUG(std::cerr << "AntBlocks: ";
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for (unsigned i = 0, e = AnticipatibleBlocks.size(); i != e; ++i)
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if (AnticipatibleBlocks[i])
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std::cerr << BlockMapping[i]->getName() <<" ";
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std::cerr << "\n";);
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// AvailabilityFrontier - Calculates the availability frontier for the current
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// expression. The availability frontier contains the blocks on the dominance
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// frontier of the current available expressions, iff they anticipate a
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// definition of the expression.
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hash_set<unsigned> AvailabilityFrontier;
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Instruction *NonPHIOccurrence = 0;
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while (!Definitions.empty() || !AvailabilityFrontier.empty()) {
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if (!Definitions.empty() &&
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(AvailabilityFrontier.empty() ||
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Definitions.begin()->first < *AvailabilityFrontier.begin())) {
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Instruction *Occurrence = Definitions.begin()->second;
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BasicBlock *BB = Occurrence->getParent();
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Definitions.erase(Definitions.begin());
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DEBUG(std::cerr << "PROCESSING Occurrence: " << *Occurrence);
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// Check to see if there is already an incoming value for this block...
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AvailableBlocksTy::iterator LBI = AvailableBlocks.find(BB);
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if (LBI != AvailableBlocks.end()) {
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// Yes, there is a dominating definition for this block. Replace this
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// occurrence with the incoming value.
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if (LBI->second != Occurrence) {
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DEBUG(std::cerr << " replacing with: " << *LBI->second);
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Occurrence->replaceAllUsesWith(LBI->second);
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BB->getInstList().erase(Occurrence); // Delete instruction
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++NumRedundant;
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}
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} else {
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ProcessedExpressions.insert(Occurrence);
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if (!isa<PHINode>(Occurrence))
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NonPHIOccurrence = Occurrence; // Keep an occurrence of this expr
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// Okay, there is no incoming value for this block, so this expression
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// is a new definition that is good for this block and all blocks
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// dominated by it. Add this information to the AvailableBlocks map.
|
||||
//
|
||||
MarkOccurrenceAvailableInAllDominatedBlocks(Occurrence, BB);
|
||||
|
||||
// Update the dominance frontier for the definitions so far... if a node
|
||||
// in the dominator frontier now has all of its predecessors available,
|
||||
// and the block is in an anticipatible region, we can insert a PHI node
|
||||
// in that block.
|
||||
DominanceFrontier::iterator DFI = DF->find(BB);
|
||||
if (DFI != DF->end()) {
|
||||
for (std::set<BasicBlock*>::iterator DI = DFI->second.begin();
|
||||
DI != DFI->second.end(); ++DI) {
|
||||
BasicBlock *DFBlock = *DI;
|
||||
unsigned DFBlockID = BlockNumbering[DFBlock];
|
||||
if (AnticipatibleBlocks[DFBlockID]) {
|
||||
// Check to see if any of the predecessors of this block on the
|
||||
// frontier are not available...
|
||||
bool AnyNotAvailable = false;
|
||||
for (pred_iterator PI = pred_begin(DFBlock),
|
||||
PE = pred_end(DFBlock); PI != PE; ++PI)
|
||||
if (!AvailableBlocks.count(*PI)) {
|
||||
AnyNotAvailable = true;
|
||||
break;
|
||||
}
|
||||
|
||||
// If any predecessor blocks are not available, add the node to
|
||||
// the current expression dominance frontier.
|
||||
if (AnyNotAvailable) {
|
||||
AvailabilityFrontier.insert(DFBlockID);
|
||||
} else {
|
||||
// This block is no longer in the availability frontier, it IS
|
||||
// available.
|
||||
AvailabilityFrontier.erase(DFBlockID);
|
||||
|
||||
// If all of the predecessor blocks are available (and the block
|
||||
// anticipates a definition along the path to the exit), we need
|
||||
// to insert a new PHI node in this block. This block serves as
|
||||
// a new definition for the expression, extending the available
|
||||
// region.
|
||||
//
|
||||
PHINode *PN = new PHINode(ExprType, Expr->getName()+".pre",
|
||||
DFBlock->begin());
|
||||
ProcessedExpressions.insert(PN);
|
||||
|
||||
DEBUG(std::cerr << " INSERTING PHI on frontier: " << *PN);
|
||||
|
||||
// Add the incoming blocks for the PHI node
|
||||
for (pred_iterator PI = pred_begin(DFBlock),
|
||||
PE = pred_end(DFBlock); PI != PE; ++PI)
|
||||
if (*PI != DFBlock)
|
||||
PN->addIncoming(AvailableBlocks[*PI], *PI);
|
||||
else // edge from the current block
|
||||
PN->addIncoming(PN, DFBlock);
|
||||
|
||||
Instruction *&BlockOcc = Definitions[DFBlockID];
|
||||
if (BlockOcc) {
|
||||
DEBUG(std::cerr <<" PHI superceeds occurrence: "<<
|
||||
*BlockOcc);
|
||||
BlockOcc->replaceAllUsesWith(PN);
|
||||
BlockOcc->getParent()->getInstList().erase(BlockOcc);
|
||||
++NumRedundant;
|
||||
}
|
||||
BlockOcc = PN;
|
||||
}
|
||||
}
|
||||
}
|
||||
}
|
||||
}
|
||||
|
||||
} else {
|
||||
// Otherwise we must be looking at a node in the availability frontier!
|
||||
unsigned AFBlockID = *AvailabilityFrontier.begin();
|
||||
AvailabilityFrontier.erase(AvailabilityFrontier.begin());
|
||||
BasicBlock *AFBlock = BlockMapping[AFBlockID];
|
||||
|
||||
// We eliminate the partial redundancy on this frontier by inserting a PHI
|
||||
// node into this block, merging any incoming available versions into the
|
||||
// PHI and inserting a new computation into predecessors without an
|
||||
// incoming value. Note that we would have to insert the expression on
|
||||
// the edge if the predecessor didn't anticipate the expression and we
|
||||
// didn't break critical edges.
|
||||
//
|
||||
PHINode *PN = new PHINode(ExprType, Expr->getName()+".PRE",
|
||||
AFBlock->begin());
|
||||
DEBUG(std::cerr << "INSERTING PHI for PR: " << *PN);
|
||||
|
||||
// If there is a pending occurrence in this block, make sure to replace it
|
||||
// with the PHI node...
|
||||
std::map<unsigned, Instruction*>::iterator EDFI =
|
||||
Definitions.find(AFBlockID);
|
||||
if (EDFI != Definitions.end()) {
|
||||
// There is already an occurrence in this block. Replace it with PN and
|
||||
// remove it.
|
||||
Instruction *OldOcc = EDFI->second;
|
||||
DEBUG(std::cerr << " Replaces occurrence: " << *OldOcc);
|
||||
OldOcc->replaceAllUsesWith(PN);
|
||||
AFBlock->getInstList().erase(OldOcc);
|
||||
Definitions.erase(EDFI);
|
||||
++NumRedundant;
|
||||
}
|
||||
|
||||
for (pred_iterator PI = pred_begin(AFBlock), PE = pred_end(AFBlock);
|
||||
PI != PE; ++PI) {
|
||||
BasicBlock *Pred = *PI;
|
||||
AvailableBlocksTy::iterator LBI = AvailableBlocks.find(Pred);
|
||||
if (LBI != AvailableBlocks.end()) { // If there is a available value
|
||||
PN->addIncoming(LBI->second, Pred); // for this pred, use it.
|
||||
} else { // No available value yet...
|
||||
unsigned PredID = BlockNumbering[Pred];
|
||||
|
||||
// Is the predecessor the same block that we inserted the PHI into?
|
||||
// (self loop)
|
||||
if (Pred == AFBlock) {
|
||||
// Yes, reuse the incoming value here...
|
||||
PN->addIncoming(PN, Pred);
|
||||
} else {
|
||||
// No, we must insert a new computation into this block and add it
|
||||
// to the definitions list...
|
||||
assert(NonPHIOccurrence && "No non-phi occurrences seen so far???");
|
||||
Instruction *New = NonPHIOccurrence->clone();
|
||||
New->setName(NonPHIOccurrence->getName() + ".PRE-inserted");
|
||||
ProcessedExpressions.insert(New);
|
||||
|
||||
DEBUG(std::cerr << " INSERTING OCCURRRENCE: " << *New);
|
||||
|
||||
// Insert it into the bottom of the predecessor, right before the
|
||||
// terminator instruction...
|
||||
Pred->getInstList().insert(Pred->getTerminator(), New);
|
||||
|
||||
// Make this block be the available definition for any blocks it
|
||||
// dominates. The ONLY case that this can affect more than just the
|
||||
// block itself is when we are moving a computation to a loop
|
||||
// header. In all other cases, because we don't have critical
|
||||
// edges, the node is guaranteed to only dominate itself.
|
||||
//
|
||||
ReplaceDominatedAvailableOccurrencesWith(New, DT->getNode(Pred));
|
||||
|
||||
// Add it as an incoming value on this edge to the PHI node
|
||||
PN->addIncoming(New, Pred);
|
||||
NonPHIOccurrence = New;
|
||||
NumInserted++;
|
||||
}
|
||||
}
|
||||
}
|
||||
|
||||
// Find out if there is already an available value in this block. If so,
|
||||
// we need to replace the available value with the PHI node. This can
|
||||
// only happen when we just inserted a PHI node on a backedge.
|
||||
//
|
||||
AvailableBlocksTy::iterator LBBlockAvailableValIt =
|
||||
AvailableBlocks.find(AFBlock);
|
||||
if (LBBlockAvailableValIt != AvailableBlocks.end()) {
|
||||
if (LBBlockAvailableValIt->second->getParent() == AFBlock) {
|
||||
Instruction *OldVal = LBBlockAvailableValIt->second;
|
||||
OldVal->replaceAllUsesWith(PN); // Use the new PHI node now
|
||||
++NumRedundant;
|
||||
DEBUG(std::cerr << " PHI replaces available value: %"
|
||||
<< OldVal->getName() << "\n");
|
||||
|
||||
// Loop over all of the blocks dominated by this PHI node, and change
|
||||
// the AvailableBlocks entries to be the PHI node instead of the old
|
||||
// instruction.
|
||||
MarkOccurrenceAvailableInAllDominatedBlocks(PN, AFBlock);
|
||||
|
||||
AFBlock->getInstList().erase(OldVal); // Delete old instruction!
|
||||
|
||||
// The resultant PHI node is a new definition of the value!
|
||||
Definitions.insert(std::make_pair(AFBlockID, PN));
|
||||
} else {
|
||||
// If the value is not defined in this block, that means that an
|
||||
// inserted occurrence in a predecessor is now the live value for the
|
||||
// region (occurs when hoisting loop invariants, f.e.). In this case,
|
||||
// the PHI node should actually just be removed.
|
||||
assert(PN->use_empty() && "No uses should exist for dead PHI node!");
|
||||
PN->getParent()->getInstList().erase(PN);
|
||||
}
|
||||
} else {
|
||||
// The resultant PHI node is a new definition of the value!
|
||||
Definitions.insert(std::make_pair(AFBlockID, PN));
|
||||
}
|
||||
}
|
||||
}
|
||||
|
||||
AvailableBlocks.clear();
|
||||
|
||||
return Changed;
|
||||
}
|
||||
|
||||
Loading…
Reference in New Issue