llvm/lib/CodeGen/StrongPHIElimination.cpp
2007-11-06 04:49:43 +00:00

215 lines
6.6 KiB
C++

//===- StrongPhiElimination.cpp - Eliminate PHI nodes by inserting copies -===//
//
// The LLVM Compiler Infrastructure
//
// This file was developed by Owen Anderson and is distributed under
// the University of Illinois Open Source License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This pass eliminates machine instruction PHI nodes by inserting copy
// instructions, using an intelligent copy-folding technique based on
// dominator information. This is technique is derived from:
//
// Budimlic, et al. Fast copy coalescing and live-range identification.
// In Proceedings of the ACM SIGPLAN 2002 Conference on Programming Language
// Design and Implementation (Berlin, Germany, June 17 - 19, 2002).
// PLDI '02. ACM, New York, NY, 25-32.
// DOI= http://doi.acm.org/10.1145/512529.512534
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "strongphielim"
#include "llvm/CodeGen/Passes.h"
#include "llvm/CodeGen/LiveVariables.h"
#include "llvm/CodeGen/MachineDominators.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Support/Compiler.h"
using namespace llvm;
namespace {
struct VISIBILITY_HIDDEN StrongPHIElimination : public MachineFunctionPass {
static char ID; // Pass identification, replacement for typeid
StrongPHIElimination() : MachineFunctionPass((intptr_t)&ID) {}
bool runOnMachineFunction(MachineFunction &Fn);
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.addPreserved<LiveVariables>();
AU.addPreservedID(PHIEliminationID);
AU.addRequired<MachineDominatorTree>();
AU.addRequired<LiveVariables>();
AU.setPreservesAll();
MachineFunctionPass::getAnalysisUsage(AU);
}
virtual void releaseMemory() {
preorder.clear();
maxpreorder.clear();
waiting.clear();
}
private:
struct DomForestNode {
private:
std::vector<DomForestNode*> children;
MachineInstr* instr;
void addChild(DomForestNode* DFN) { children.push_back(DFN); }
public:
typedef std::vector<DomForestNode*>::iterator iterator;
DomForestNode(MachineInstr* MI, DomForestNode* parent) : instr(MI) {
if (parent)
parent->addChild(this);
}
~DomForestNode() {
for (iterator I = begin(), E = end(); I != E; ++I)
delete *I;
}
inline MachineInstr* getInstr() { return instr; }
inline DomForestNode::iterator begin() { return children.begin(); }
inline DomForestNode::iterator end() { return children.end(); }
};
DenseMap<MachineBasicBlock*, unsigned> preorder;
DenseMap<MachineBasicBlock*, unsigned> maxpreorder;
DenseMap<MachineBasicBlock*, std::vector<MachineInstr*> > waiting;
void computeDFS(MachineFunction& MF);
std::vector<DomForestNode*>
computeDomForest(SmallPtrSet<MachineInstr*, 8>& instrs);
};
char StrongPHIElimination::ID = 0;
RegisterPass<StrongPHIElimination> X("strong-phi-node-elimination",
"Eliminate PHI nodes for register allocation, intelligently");
}
const PassInfo *llvm::StrongPHIEliminationID = X.getPassInfo();
/// computeDFS - Computes the DFS-in and DFS-out numbers of the dominator tree
/// of the given MachineFunction. These numbers are then used in other parts
/// of the PHI elimination process.
void StrongPHIElimination::computeDFS(MachineFunction& MF) {
SmallPtrSet<MachineDomTreeNode*, 8> frontier;
SmallPtrSet<MachineDomTreeNode*, 8> visited;
unsigned time = 0;
MachineDominatorTree& DT = getAnalysis<MachineDominatorTree>();
MachineDomTreeNode* node = DT.getRootNode();
std::vector<MachineDomTreeNode*> worklist;
worklist.push_back(node);
while (!worklist.empty()) {
MachineDomTreeNode* currNode = worklist.back();
if (!frontier.count(currNode)) {
frontier.insert(currNode);
++time;
preorder.insert(std::make_pair(currNode->getBlock(), time));
}
bool inserted = false;
for (MachineDomTreeNode::iterator I = node->begin(), E = node->end();
I != E; ++I)
if (!frontier.count(*I) && !visited.count(*I)) {
worklist.push_back(*I);
inserted = true;
break;
}
if (!inserted) {
frontier.erase(currNode);
visited.insert(currNode);
maxpreorder.insert(std::make_pair(currNode->getBlock(), time));
worklist.pop_back();
}
}
}
class PreorderSorter {
private:
DenseMap<MachineBasicBlock*, unsigned>& preorder;
public:
PreorderSorter(DenseMap<MachineBasicBlock*, unsigned>& p) : preorder(p) { }
bool operator()(MachineInstr* A, MachineInstr* B) {
if (A == B)
return false;
if (preorder[A->getParent()] < preorder[B->getParent()])
return true;
else if (preorder[A->getParent()] > preorder[B->getParent()])
return false;
if (A->getOpcode() == TargetInstrInfo::PHI &&
B->getOpcode() == TargetInstrInfo::PHI)
return A < B;
MachineInstr* begin = A->getParent()->begin();
return std::distance(begin, A) < std::distance(begin, B);
}
};
std::vector<StrongPHIElimination::DomForestNode*>
StrongPHIElimination::computeDomForest(SmallPtrSet<MachineInstr*, 8>& instrs) {
DomForestNode* VirtualRoot = new DomForestNode(0, 0);
maxpreorder.insert(std::make_pair((MachineBasicBlock*)0, ~0UL));
std::vector<MachineInstr*> worklist;
worklist.reserve(instrs.size());
for (SmallPtrSet<MachineInstr*, 8>::iterator I = instrs.begin(),
E = instrs.end(); I != E; ++I)
worklist.push_back(*I);
PreorderSorter PS(preorder);
std::sort(worklist.begin(), worklist.end(), PS);
DomForestNode* CurrentParent = VirtualRoot;
std::vector<DomForestNode*> stack;
stack.push_back(VirtualRoot);
for (std::vector<MachineInstr*>::iterator I = worklist.begin(),
E = worklist.end(); I != E; ++I) {
while (preorder[(*I)->getParent()] >
maxpreorder[CurrentParent->getInstr()->getParent()]) {
stack.pop_back();
CurrentParent = stack.back();
}
DomForestNode* child = new DomForestNode(*I, CurrentParent);
stack.push_back(child);
CurrentParent = child;
}
std::vector<DomForestNode*> ret;
ret.insert(ret.end(), VirtualRoot->begin(), VirtualRoot->end());
return ret;
}
bool StrongPHIElimination::runOnMachineFunction(MachineFunction &Fn) {
computeDFS(Fn);
return false;
}