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112 lines
3.6 KiB
C++
112 lines
3.6 KiB
C++
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//===- StrongPhiElimination.cpp - Eliminate PHI nodes by inserting copies -===//
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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 Owen Anderson 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 pass eliminates machine instruction PHI nodes by inserting copy
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// instructions, using an intelligent copy-folding technique based on
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// dominator information. This is technique is derived from:
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//
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// Budimlic, et al. Fast copy coalescing and live-range identification.
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// In Proceedings of the ACM SIGPLAN 2002 Conference on Programming Language
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// Design and Implementation (Berlin, Germany, June 17 - 19, 2002).
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// PLDI '02. ACM, New York, NY, 25-32.
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// DOI= http://doi.acm.org/10.1145/512529.512534
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//
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "strongphielim"
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#include "llvm/CodeGen/Passes.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/MachineInstr.h"
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#include "llvm/Target/TargetInstrInfo.h"
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#include "llvm/Target/TargetMachine.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/Support/Compiler.h"
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using namespace llvm;
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namespace {
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struct VISIBILITY_HIDDEN StrongPHIElimination : public MachineFunctionPass {
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static char ID; // Pass identification, replacement for typeid
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StrongPHIElimination() : MachineFunctionPass((intptr_t)&ID) {}
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bool runOnMachineFunction(MachineFunction &Fn) {
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computeDFS(Fn);
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return false;
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}
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virtual void getAnalysisUsage(AnalysisUsage &AU) const {
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AU.addRequired<MachineDominatorTree>();
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MachineFunctionPass::getAnalysisUsage(AU);
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}
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virtual void releaseMemory() {
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preorder.clear();
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maxpreorder.clear();
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}
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private:
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DenseMap<MachineBasicBlock*, unsigned> preorder;
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DenseMap<MachineBasicBlock*, unsigned> maxpreorder;
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void computeDFS(MachineFunction& MF);
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};
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char StrongPHIElimination::ID = 0;
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RegisterPass<StrongPHIElimination> X("strong-phi-node-elimination",
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"Eliminate PHI nodes for register allocation, intelligently");
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}
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const PassInfo *llvm::StrongPHIEliminationID = X.getPassInfo();
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/// computeDFS - Computes the DFS-in and DFS-out numbers of the dominator tree
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/// of the given MachineFunction. These numbers are then used in other parts
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/// of the PHI elimination process.
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void StrongPHIElimination::computeDFS(MachineFunction& MF) {
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SmallPtrSet<MachineDomTreeNode*, 8> frontier;
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SmallPtrSet<MachineDomTreeNode*, 8> visited;
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unsigned time = 0;
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MachineDominatorTree& DT = getAnalysis<MachineDominatorTree>();
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MachineDomTreeNode* node = DT.getRootNode();
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std::vector<MachineDomTreeNode*> worklist;
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worklist.push_back(node);
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while (!worklist.empty()) {
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MachineDomTreeNode* currNode = worklist.back();
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if (!frontier.count(currNode)) {
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frontier.insert(currNode);
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++time;
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preorder.insert(std::make_pair(currNode->getBlock(), time));
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}
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bool inserted = false;
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for (MachineDomTreeNode::iterator I = node->begin(), E = node->end();
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I != E; ++I)
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if (!frontier.count(*I) && !visited.count(*I)) {
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worklist.push_back(*I);
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inserted = true;
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break;
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}
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if (!inserted) {
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frontier.erase(currNode);
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visited.insert(currNode);
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maxpreorder.insert(std::make_pair(currNode->getBlock(), time));
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worklist.pop_back();
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}
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}
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}
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