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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@45738 91177308-0d34-0410-b5e6-96231b3b80d8
657 lines
22 KiB
C++
657 lines
22 KiB
C++
//===- 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 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 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/LiveVariables.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/CodeGen/MachineRegisterInfo.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/DepthFirstIterator.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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DenseMap<MachineBasicBlock*,
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std::map<unsigned, unsigned> > Waiting;
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std::map<unsigned, std::vector<unsigned> > Stacks;
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std::set<unsigned> UsedByAnother;
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bool runOnMachineFunction(MachineFunction &Fn);
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virtual void getAnalysisUsage(AnalysisUsage &AU) const {
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AU.addRequired<MachineDominatorTree>();
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AU.addRequired<LiveVariables>();
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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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Waiting.clear();
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}
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private:
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struct DomForestNode {
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private:
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std::vector<DomForestNode*> children;
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unsigned reg;
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void addChild(DomForestNode* DFN) { children.push_back(DFN); }
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public:
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typedef std::vector<DomForestNode*>::iterator iterator;
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DomForestNode(unsigned r, DomForestNode* parent) : reg(r) {
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if (parent)
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parent->addChild(this);
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}
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~DomForestNode() {
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for (iterator I = begin(), E = end(); I != E; ++I)
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delete *I;
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}
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inline unsigned getReg() { return reg; }
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inline DomForestNode::iterator begin() { return children.begin(); }
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inline DomForestNode::iterator end() { return children.end(); }
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};
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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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void processBlock(MachineBasicBlock* MBB);
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std::vector<DomForestNode*> computeDomForest(std::set<unsigned>& instrs);
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void processPHIUnion(MachineInstr* Inst,
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std::set<unsigned>& PHIUnion,
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std::vector<StrongPHIElimination::DomForestNode*>& DF,
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std::vector<std::pair<unsigned, unsigned> >& locals);
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void ScheduleCopies(MachineBasicBlock* MBB, std::set<unsigned>& pushed);
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void InsertCopies(MachineBasicBlock* MBB);
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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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/// PreorderSorter - a helper class that is used to sort registers
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/// according to the preorder number of their defining blocks
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class PreorderSorter {
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private:
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DenseMap<MachineBasicBlock*, unsigned>& preorder;
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LiveVariables& LV;
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public:
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PreorderSorter(DenseMap<MachineBasicBlock*, unsigned>& p,
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LiveVariables& L) : preorder(p), LV(L) { }
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bool operator()(unsigned A, unsigned B) {
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if (A == B)
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return false;
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MachineBasicBlock* ABlock = LV.getVarInfo(A).DefInst->getParent();
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MachineBasicBlock* BBlock = LV.getVarInfo(A).DefInst->getParent();
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if (preorder[ABlock] < preorder[BBlock])
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return true;
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else if (preorder[ABlock] > preorder[BBlock])
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return false;
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assert(0 && "Error sorting by dominance!");
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return false;
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}
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};
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/// computeDomForest - compute the subforest of the DomTree corresponding
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/// to the defining blocks of the registers in question
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std::vector<StrongPHIElimination::DomForestNode*>
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StrongPHIElimination::computeDomForest(std::set<unsigned>& regs) {
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LiveVariables& LV = getAnalysis<LiveVariables>();
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DomForestNode* VirtualRoot = new DomForestNode(0, 0);
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maxpreorder.insert(std::make_pair((MachineBasicBlock*)0, ~0UL));
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std::vector<unsigned> worklist;
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worklist.reserve(regs.size());
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for (std::set<unsigned>::iterator I = regs.begin(), E = regs.end();
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I != E; ++I)
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worklist.push_back(*I);
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PreorderSorter PS(preorder, LV);
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std::sort(worklist.begin(), worklist.end(), PS);
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DomForestNode* CurrentParent = VirtualRoot;
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std::vector<DomForestNode*> stack;
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stack.push_back(VirtualRoot);
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for (std::vector<unsigned>::iterator I = worklist.begin(), E = worklist.end();
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I != E; ++I) {
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unsigned pre = preorder[LV.getVarInfo(*I).DefInst->getParent()];
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MachineBasicBlock* parentBlock =
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LV.getVarInfo(CurrentParent->getReg()).DefInst->getParent();
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while (pre > maxpreorder[parentBlock]) {
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stack.pop_back();
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CurrentParent = stack.back();
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parentBlock = LV.getVarInfo(CurrentParent->getReg()).DefInst->getParent();
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}
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DomForestNode* child = new DomForestNode(*I, CurrentParent);
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stack.push_back(child);
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CurrentParent = child;
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}
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std::vector<DomForestNode*> ret;
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ret.insert(ret.end(), VirtualRoot->begin(), VirtualRoot->end());
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return ret;
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}
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/// isLiveIn - helper method that determines, from a VarInfo, if a register
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/// is live into a block
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static bool isLiveIn(LiveVariables::VarInfo& V, MachineBasicBlock* MBB) {
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if (V.AliveBlocks.test(MBB->getNumber()))
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return true;
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if (V.DefInst->getParent() != MBB &&
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V.UsedBlocks.test(MBB->getNumber()))
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return true;
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return false;
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}
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/// isLiveOut - help method that determines, from a VarInfo, if a register is
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/// live out of a block.
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static bool isLiveOut(LiveVariables::VarInfo& V, MachineBasicBlock* MBB) {
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if (MBB == V.DefInst->getParent() ||
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V.UsedBlocks.test(MBB->getNumber())) {
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for (std::vector<MachineInstr*>::iterator I = V.Kills.begin(),
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E = V.Kills.end(); I != E; ++I)
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if ((*I)->getParent() == MBB)
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return false;
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return true;
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}
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return false;
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}
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/// isKillInst - helper method that determines, from a VarInfo, if an
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/// instruction kills a given register
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static bool isKillInst(LiveVariables::VarInfo& V, MachineInstr* MI) {
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return std::find(V.Kills.begin(), V.Kills.end(), MI) != V.Kills.end();
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}
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/// interferes - checks for local interferences by scanning a block. The only
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/// trick parameter is 'mode' which tells it the relationship of the two
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/// registers. 0 - defined in the same block, 1 - first properly dominates
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/// second, 2 - second properly dominates first
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static bool interferes(LiveVariables::VarInfo& First, LiveVariables::VarInfo& Second,
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MachineBasicBlock* scan, unsigned mode) {
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MachineInstr* def = 0;
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MachineInstr* kill = 0;
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bool interference = false;
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// Wallk the block, checking for interferences
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for (MachineBasicBlock::iterator MBI = scan->begin(), MBE = scan->end();
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MBI != MBE; ++MBI) {
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MachineInstr* curr = MBI;
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// Same defining block...
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if (mode == 0) {
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if (curr == First.DefInst) {
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// If we find our first DefInst, save it
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if (!def) {
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def = curr;
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// If there's already an unkilled DefInst, then
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// this is an interference
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} else if (!kill) {
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interference = true;
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break;
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// If there's a DefInst followed by a KillInst, then
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// they can't interfere
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} else {
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interference = false;
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break;
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}
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// Symmetric with the above
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} else if (curr == Second.DefInst ) {
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if (!def) {
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def = curr;
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} else if (!kill) {
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interference = true;
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break;
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} else {
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interference = false;
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break;
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}
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// Store KillInsts if they match up with the DefInst
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} else if (isKillInst(First, curr)) {
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if (def == First.DefInst) {
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kill = curr;
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} else if (isKillInst(Second, curr)) {
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if (def == Second.DefInst) {
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kill = curr;
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}
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}
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}
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// First properly dominates second...
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} else if (mode == 1) {
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if (curr == Second.DefInst) {
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// DefInst of second without kill of first is an interference
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if (!kill) {
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interference = true;
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break;
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// DefInst after a kill is a non-interference
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} else {
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interference = false;
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break;
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}
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// Save KillInsts of First
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} else if (isKillInst(First, curr)) {
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kill = curr;
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}
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// Symmetric with the above
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} else if (mode == 2) {
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if (curr == First.DefInst) {
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if (!kill) {
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interference = true;
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break;
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} else {
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interference = false;
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break;
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}
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} else if (isKillInst(Second, curr)) {
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kill = curr;
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}
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}
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}
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return interference;
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}
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/// processBlock - Eliminate PHIs in the given block
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void StrongPHIElimination::processBlock(MachineBasicBlock* MBB) {
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LiveVariables& LV = getAnalysis<LiveVariables>();
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// Holds names that have been added to a set in any PHI within this block
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// before the current one.
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std::set<unsigned> ProcessedNames;
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MachineBasicBlock::iterator P = MBB->begin();
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while (P->getOpcode() == TargetInstrInfo::PHI) {
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LiveVariables::VarInfo& PHIInfo = LV.getVarInfo(P->getOperand(0).getReg());
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unsigned DestReg = P->getOperand(0).getReg();
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// Hold the names that are currently in the candidate set.
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std::set<unsigned> PHIUnion;
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std::set<MachineBasicBlock*> UnionedBlocks;
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for (int i = P->getNumOperands() - 1; i >= 2; i-=2) {
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unsigned SrcReg = P->getOperand(i-1).getReg();
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LiveVariables::VarInfo& SrcInfo = LV.getVarInfo(SrcReg);
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// Check for trivial interferences
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if (isLiveIn(SrcInfo, P->getParent()) ||
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isLiveOut(PHIInfo, SrcInfo.DefInst->getParent()) ||
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( PHIInfo.DefInst->getOpcode() == TargetInstrInfo::PHI &&
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isLiveIn(PHIInfo, SrcInfo.DefInst->getParent()) ) ||
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ProcessedNames.count(SrcReg) ||
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UnionedBlocks.count(SrcInfo.DefInst->getParent())) {
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// add a copy from a_i to p in Waiting[From[a_i]]
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MachineBasicBlock* From = P->getOperand(i).getMBB();
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Waiting[From].insert(std::make_pair(SrcReg, DestReg));
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UsedByAnother.insert(SrcReg);
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} else {
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PHIUnion.insert(SrcReg);
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UnionedBlocks.insert(SrcInfo.DefInst->getParent());
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}
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}
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std::vector<StrongPHIElimination::DomForestNode*> DF =
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computeDomForest(PHIUnion);
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// Walk DomForest to resolve interferences
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std::vector<std::pair<unsigned, unsigned> > localInterferences;
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processPHIUnion(P, PHIUnion, DF, localInterferences);
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// Check for local interferences
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for (std::vector<std::pair<unsigned, unsigned> >::iterator I =
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localInterferences.begin(), E = localInterferences.end(); I != E; ++I) {
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std::pair<unsigned, unsigned> p = *I;
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LiveVariables::VarInfo& FirstInfo = LV.getVarInfo(p.first);
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LiveVariables::VarInfo& SecondInfo = LV.getVarInfo(p.second);
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MachineDominatorTree& MDT = getAnalysis<MachineDominatorTree>();
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// Determine the block we need to scan and the relationship between
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// the two registers
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MachineBasicBlock* scan = 0;
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unsigned mode = 0;
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if (FirstInfo.DefInst->getParent() == SecondInfo.DefInst->getParent()) {
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scan = FirstInfo.DefInst->getParent();
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mode = 0; // Same block
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} else if (MDT.dominates(FirstInfo.DefInst->getParent(),
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SecondInfo.DefInst->getParent())) {
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scan = SecondInfo.DefInst->getParent();
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mode = 1; // First dominates second
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} else {
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scan = FirstInfo.DefInst->getParent();
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mode = 2; // Second dominates first
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}
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// If there's an interference, we need to insert copies
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if (interferes(FirstInfo, SecondInfo, scan, mode)) {
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// Insert copies for First
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for (int i = P->getNumOperands() - 1; i >= 2; i-=2) {
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if (P->getOperand(i-1).getReg() == p.first) {
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unsigned SrcReg = p.first;
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MachineBasicBlock* From = P->getOperand(i).getMBB();
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Waiting[From].insert(std::make_pair(SrcReg,
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P->getOperand(0).getReg()));
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UsedByAnother.insert(SrcReg);
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PHIUnion.erase(SrcReg);
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}
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}
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}
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}
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// FIXME: Cache renaming information
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ProcessedNames.insert(PHIUnion.begin(), PHIUnion.end());
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++P;
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}
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}
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/// processPHIUnion - Take a set of candidate registers to be coallesced when
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/// decomposing the PHI instruction. Use the DominanceForest to remove the ones
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/// that are known to interfere, and flag others that need to be checked for
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/// local interferences.
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void StrongPHIElimination::processPHIUnion(MachineInstr* Inst,
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std::set<unsigned>& PHIUnion,
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std::vector<StrongPHIElimination::DomForestNode*>& DF,
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std::vector<std::pair<unsigned, unsigned> >& locals) {
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std::vector<DomForestNode*> worklist(DF.begin(), DF.end());
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SmallPtrSet<DomForestNode*, 4> visited;
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LiveVariables& LV = getAnalysis<LiveVariables>();
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unsigned DestReg = Inst->getOperand(0).getReg();
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// DF walk on the DomForest
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while (!worklist.empty()) {
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DomForestNode* DFNode = worklist.back();
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LiveVariables::VarInfo& Info = LV.getVarInfo(DFNode->getReg());
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visited.insert(DFNode);
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bool inserted = false;
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for (DomForestNode::iterator CI = DFNode->begin(), CE = DFNode->end();
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CI != CE; ++CI) {
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DomForestNode* child = *CI;
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LiveVariables::VarInfo& CInfo = LV.getVarInfo(child->getReg());
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if (isLiveOut(Info, CInfo.DefInst->getParent())) {
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// Insert copies for parent
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for (int i = Inst->getNumOperands() - 1; i >= 2; i-=2) {
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if (Inst->getOperand(i-1).getReg() == DFNode->getReg()) {
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unsigned SrcReg = DFNode->getReg();
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MachineBasicBlock* From = Inst->getOperand(i).getMBB();
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Waiting[From].insert(std::make_pair(SrcReg, DestReg));
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UsedByAnother.insert(SrcReg);
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PHIUnion.erase(SrcReg);
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}
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}
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} else if (isLiveIn(Info, CInfo.DefInst->getParent()) ||
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Info.DefInst->getParent() == CInfo.DefInst->getParent()) {
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// Add (p, c) to possible local interferences
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locals.push_back(std::make_pair(DFNode->getReg(), child->getReg()));
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}
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if (!visited.count(child)) {
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worklist.push_back(child);
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|
inserted = true;
|
|
}
|
|
}
|
|
|
|
if (!inserted) worklist.pop_back();
|
|
}
|
|
}
|
|
|
|
/// ScheduleCopies - Insert copies into predecessor blocks, scheduling
|
|
/// them properly so as to avoid the 'lost copy' and the 'virtual swap'
|
|
/// problems.
|
|
///
|
|
/// Based on "Practical Improvements to the Construction and Destruction
|
|
/// of Static Single Assignment Form" by Briggs, et al.
|
|
void StrongPHIElimination::ScheduleCopies(MachineBasicBlock* MBB,
|
|
std::set<unsigned>& pushed) {
|
|
// FIXME: This function needs to update LiveVariables
|
|
std::map<unsigned, unsigned>& copy_set= Waiting[MBB];
|
|
|
|
std::map<unsigned, unsigned> worklist;
|
|
std::map<unsigned, unsigned> map;
|
|
|
|
// Setup worklist of initial copies
|
|
for (std::map<unsigned, unsigned>::iterator I = copy_set.begin(),
|
|
E = copy_set.end(); I != E; ) {
|
|
map.insert(std::make_pair(I->first, I->first));
|
|
map.insert(std::make_pair(I->second, I->second));
|
|
|
|
if (!UsedByAnother.count(I->first)) {
|
|
worklist.insert(*I);
|
|
|
|
// Avoid iterator invalidation
|
|
unsigned first = I->first;
|
|
++I;
|
|
copy_set.erase(first);
|
|
} else {
|
|
++I;
|
|
}
|
|
}
|
|
|
|
LiveVariables& LV = getAnalysis<LiveVariables>();
|
|
MachineFunction* MF = MBB->getParent();
|
|
const TargetInstrInfo *TII = MF->getTarget().getInstrInfo();
|
|
|
|
// Iterate over the worklist, inserting copies
|
|
while (!worklist.empty() || !copy_set.empty()) {
|
|
while (!worklist.empty()) {
|
|
std::pair<unsigned, unsigned> curr = *worklist.begin();
|
|
worklist.erase(curr.first);
|
|
|
|
const TargetRegisterClass *RC = MF->getRegInfo().getRegClass(curr.first);
|
|
|
|
if (isLiveOut(LV.getVarInfo(curr.second), MBB)) {
|
|
// Create a temporary
|
|
unsigned t = MF->getRegInfo().createVirtualRegister(RC);
|
|
|
|
// Insert copy from curr.second to a temporary at
|
|
// the Phi defining curr.second
|
|
LiveVariables::VarInfo VI = LV.getVarInfo(curr.second);
|
|
MachineBasicBlock::iterator PI = VI.DefInst;
|
|
TII->copyRegToReg(*VI.DefInst->getParent(), PI, t,
|
|
curr.second, RC, RC);
|
|
|
|
// Push temporary on Stacks
|
|
Stacks[curr.second].push_back(t);
|
|
|
|
// Insert curr.second in pushed
|
|
pushed.insert(curr.second);
|
|
}
|
|
|
|
// Insert copy from map[curr.first] to curr.second
|
|
TII->copyRegToReg(*MBB, MBB->end(), curr.second,
|
|
map[curr.first], RC, RC);
|
|
map[curr.first] = curr.second;
|
|
|
|
// If curr.first is a destination in copy_set...
|
|
for (std::map<unsigned, unsigned>::iterator I = copy_set.begin(),
|
|
E = copy_set.end(); I != E; )
|
|
if (curr.first == I->second) {
|
|
std::pair<unsigned, unsigned> temp = *I;
|
|
|
|
// Avoid iterator invalidation
|
|
++I;
|
|
copy_set.erase(temp.first);
|
|
worklist.insert(temp);
|
|
|
|
break;
|
|
} else {
|
|
++I;
|
|
}
|
|
}
|
|
|
|
if (!copy_set.empty()) {
|
|
std::pair<unsigned, unsigned> curr = *copy_set.begin();
|
|
copy_set.erase(curr.first);
|
|
|
|
const TargetRegisterClass *RC = MF->getRegInfo().getRegClass(curr.first);
|
|
|
|
// Insert a copy from dest to a new temporary t at the end of b
|
|
unsigned t = MF->getRegInfo().createVirtualRegister(RC);
|
|
TII->copyRegToReg(*MBB, MBB->end(), t,
|
|
curr.second, RC, RC);
|
|
map[curr.second] = t;
|
|
|
|
worklist.insert(curr);
|
|
}
|
|
}
|
|
}
|
|
|
|
/// InsertCopies - insert copies into MBB and all of its successors
|
|
void StrongPHIElimination::InsertCopies(MachineBasicBlock* MBB) {
|
|
std::set<unsigned> pushed;
|
|
|
|
// Rewrite register uses from Stacks
|
|
for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end();
|
|
I != E; ++I)
|
|
for (unsigned i = 0; i < I->getNumOperands(); ++i)
|
|
if (I->getOperand(i).isRegister() &&
|
|
Stacks[I->getOperand(i).getReg()].size()) {
|
|
I->getOperand(i).setReg(Stacks[I->getOperand(i).getReg()].back());
|
|
}
|
|
|
|
// Schedule the copies for this block
|
|
ScheduleCopies(MBB, pushed);
|
|
|
|
// Recur to our successors
|
|
for (GraphTraits<MachineBasicBlock*>::ChildIteratorType I =
|
|
GraphTraits<MachineBasicBlock*>::child_begin(MBB), E =
|
|
GraphTraits<MachineBasicBlock*>::child_end(MBB); I != E; ++I)
|
|
InsertCopies(*I);
|
|
|
|
// As we exit this block, pop the names we pushed while processing it
|
|
for (std::set<unsigned>::iterator I = pushed.begin(),
|
|
E = pushed.end(); I != E; ++I)
|
|
Stacks[*I].pop_back();
|
|
}
|
|
|
|
bool StrongPHIElimination::runOnMachineFunction(MachineFunction &Fn) {
|
|
// Compute DFS numbers of each block
|
|
computeDFS(Fn);
|
|
|
|
// Determine which phi node operands need copies
|
|
for (MachineFunction::iterator I = Fn.begin(), E = Fn.end(); I != E; ++I)
|
|
if (!I->empty() &&
|
|
I->begin()->getOpcode() == TargetInstrInfo::PHI)
|
|
processBlock(I);
|
|
|
|
// Insert copies
|
|
// FIXME: This process should probably preserve LiveVariables
|
|
InsertCopies(Fn.begin());
|
|
|
|
// FIXME: Perform renaming
|
|
// FIXME: Remove Phi instrs
|
|
|
|
return false;
|
|
}
|