mirror of
https://github.com/c64scene-ar/llvm-6502.git
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ed2ffa25a1
interfered with other registers. Seems like that might be a good thing to do. :-) git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@44902 91177308-0d34-0410-b5e6-96231b3b80d8
443 lines
15 KiB
C++
443 lines
15 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 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/BreakCriticalMachineEdge.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/SSARegMap.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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DenseMap<MachineBasicBlock*,
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SmallVector<std::pair<unsigned, unsigned>, 2> > Waiting;
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bool runOnMachineFunction(MachineFunction &Fn);
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virtual void getAnalysisUsage(AnalysisUsage &AU) const {
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AU.addPreserved<LiveVariables>();
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AU.addPreservedID(PHIEliminationID);
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AU.addRequired<MachineDominatorTree>();
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AU.addRequired<LiveVariables>();
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AU.setPreservesAll();
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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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DenseMap<MachineBasicBlock*, std::vector<MachineInstr*> > waiting;
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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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void breakCriticalEdges(MachineFunction &Fn);
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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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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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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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/// 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).getMachineBasicBlock();
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Waiting[From].push_back(std::make_pair(SrcReg, DestReg));
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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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ProcessedNames.insert(PHIUnion.begin(), PHIUnion.end());
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++P;
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}
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}
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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<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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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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SmallPtrSet<DomForestNode*, 4> interferences;
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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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interferences.insert(child);
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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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// FIXME: Add (p, c) to possible local interferences
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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;
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}
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}
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if (interferences.size() == 1) {
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DomForestNode* child = *interferences.begin();
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unsigned numParentCopies = 0;
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unsigned numChildCopies = 0;
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for (int i = Inst->getNumOperands() - 1; i >= 2; i-=2) {
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unsigned SrcReg = Inst->getOperand(i-1).getReg();
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if (SrcReg == DFNode->getReg()) numParentCopies++;
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else if (SrcReg == child->getReg()) numChildCopies++;
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}
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if (numParentCopies < numChildCopies) {
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// Insert copies for child
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for (int i = Inst->getNumOperands() - 1; i >= 2; i-=2) {
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if (Inst->getOperand(i-1).getReg() == child->getReg()) {
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unsigned SrcReg = child->getReg();
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MachineBasicBlock* From = Inst->getOperand(i).getMBB();
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Waiting[From].push_back(std::make_pair(SrcReg, DestReg));
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PHIUnion.erase(SrcReg);
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}
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}
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// FIXME: Make child's children parent's children
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} else {
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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].push_back(std::make_pair(SrcReg, DestReg));
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PHIUnion.erase(SrcReg);
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}
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}
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}
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} else if (interferences.size() > 1) {
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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].push_back(std::make_pair(SrcReg, DestReg));
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PHIUnion.erase(SrcReg);
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}
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}
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}
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if (!inserted) worklist.pop_back();
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}
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}
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/// breakCriticalEdges - Break critical edges coming into blocks with PHI
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/// nodes, preserving dominator and livevariable info.
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void StrongPHIElimination::breakCriticalEdges(MachineFunction &Fn) {
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typedef std::pair<MachineBasicBlock*, MachineBasicBlock*> MBB_pair;
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MachineDominatorTree& MDT = getAnalysis<MachineDominatorTree>();
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LiveVariables& LV = getAnalysis<LiveVariables>();
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// Find critical edges
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std::vector<MBB_pair> criticals;
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for (MachineFunction::iterator I = Fn.begin(), E = Fn.end(); I != E; ++I)
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if (!I->empty() &&
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I->begin()->getOpcode() == TargetInstrInfo::PHI &&
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I->pred_size() > 1)
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for (MachineBasicBlock::pred_iterator PI = I->pred_begin(),
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PE = I->pred_end(); PI != PE; ++PI)
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if ((*PI)->succ_size() > 1)
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criticals.push_back(std::make_pair(*PI, I));
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for (std::vector<MBB_pair>::iterator I = criticals.begin(),
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E = criticals.end(); I != E; ++I) {
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// Split the edge
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MachineBasicBlock* new_bb = SplitCriticalMachineEdge(I->first, I->second);
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// Update dominators
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MDT.splitBlock(I->first);
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// Update livevariables
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for (unsigned var = 1024; var < Fn.getSSARegMap()->getLastVirtReg(); ++var)
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if (isLiveOut(LV.getVarInfo(var), I->first))
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LV.getVarInfo(var).AliveBlocks.set(new_bb->getNumber());
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}
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}
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bool StrongPHIElimination::runOnMachineFunction(MachineFunction &Fn) {
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breakCriticalEdges(Fn);
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computeDFS(Fn);
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for (MachineFunction::iterator I = Fn.begin(), E = Fn.end(); I != E; ++I)
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if (!I->empty() &&
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I->begin()->getOpcode() == TargetInstrInfo::PHI)
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processBlock(I);
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return false;
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}
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