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Sketch out an implementation of Briggs' copy placement algorithm.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@45334 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -28,6 +28,7 @@
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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/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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@ -39,7 +40,10 @@ namespace {
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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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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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@ -56,7 +60,7 @@ namespace {
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preorder.clear();
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maxpreorder.clear();
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waiting.clear();
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Waiting.clear();
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}
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private:
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@ -89,8 +93,6 @@ namespace {
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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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@ -100,7 +102,7 @@ namespace {
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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);
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};
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char StrongPHIElimination::ID = 0;
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@ -383,7 +385,8 @@ void StrongPHIElimination::processBlock(MachineBasicBlock* MBB) {
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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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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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@ -431,8 +434,10 @@ void StrongPHIElimination::processBlock(MachineBasicBlock* MBB) {
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unsigned SrcReg = p.first;
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MachineBasicBlock* From = P->getOperand(i).getMBB();
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Waiting[From].push_back(std::make_pair(SrcReg,
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P->getOperand(0).getReg()));
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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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@ -481,7 +486,9 @@ void StrongPHIElimination::processPHIUnion(MachineInstr* Inst,
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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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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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@ -501,15 +508,102 @@ void StrongPHIElimination::processPHIUnion(MachineInstr* Inst,
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}
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}
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/// ScheduleCopies - Insert copies into predecessor blocks, scheduling
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/// them properly so as to avoid the 'lost copy' and the 'virtual swap'
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/// problems.
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///
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/// Based on "Practical Improvements to the Construction and Destruction
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/// of Static Single Assignment Form" by Briggs, et al.
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void StrongPHIElimination::ScheduleCopies(MachineBasicBlock* MBB) {
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std::map<unsigned, unsigned>& copy_set= Waiting[MBB];
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std::map<unsigned, unsigned> worklist;
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std::map<unsigned, unsigned> map;
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// Setup worklist of initial copies
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for (std::map<unsigned, unsigned>::iterator I = copy_set.begin(),
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E = copy_set.end(); I != E; ) {
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map.insert(std::make_pair(I->first, I->first));
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map.insert(std::make_pair(I->second, I->second));
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if (!UsedByAnother.count(I->first)) {
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worklist.insert(*I);
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// Avoid iterator invalidation
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unsigned first = I->first;
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++I;
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copy_set.erase(first);
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} else {
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++I;
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}
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}
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LiveVariables& LV = getAnalysis<LiveVariables>();
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// Iterate over the worklist, inserting copies
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while (!worklist.empty() || !copy_set.empty()) {
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while (!worklist.empty()) {
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std::pair<unsigned, unsigned> curr = *worklist.begin();
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worklist.erase(curr.first);
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if (isLiveOut(LV.getVarInfo(curr.second), MBB)) {
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// Insert copy from curr.second to a temporary
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// Push temporary on Stacks
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}
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// Insert copy from map[curr.first] to curr.second
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map[curr.first] = curr.second;
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// If curr.first is a destination in copy_set...
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for (std::map<unsigned, unsigned>::iterator I = copy_set.begin(),
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E = copy_set.end(); I != E; )
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if (curr.first == I->second) {
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std::pair<unsigned, unsigned> temp = *I;
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// Avoid iterator invalidation
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++I;
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copy_set.erase(temp.first);
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worklist.insert(temp);
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break;
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} else {
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++I;
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}
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}
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if (!copy_set.empty()) {
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std::pair<unsigned, unsigned> curr = *copy_set.begin();
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copy_set.erase(curr.first);
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// Insert a copy from dest to a new temporary t at the end of b
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// map[curr.second] = t;
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worklist.insert(curr);
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}
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}
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}
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bool StrongPHIElimination::runOnMachineFunction(MachineFunction &Fn) {
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// Compute DFS numbers of each block
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computeDFS(Fn);
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// Determine which phi node operands need copies
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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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// FIXME: Insert copies
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// Insert copies
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MachineDominatorTree& MDT = getAnalysis<MachineDominatorTree>();
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for (df_iterator<MachineDomTreeNode*> DI = df_begin(MDT.getRootNode()),
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DE = df_end(MDT.getRootNode()); DI != DE; ++DI) {
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MachineBasicBlock* block = DI->getBlock();
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// FIXME: Do rewriting with Stacks
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ScheduleCopies(block);
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}
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// FIXME: Perform renaming
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return false;
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