#define DEBUG_TYPE "strongphielim"
#include "llvm/CodeGen/Passes.h"
+#include "llvm/CodeGen/BreakCriticalMachineEdge.h"
#include "llvm/CodeGen/LiveVariables.h"
#include "llvm/CodeGen/MachineDominators.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstr.h"
+#include "llvm/CodeGen/SSARegMap.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/ADT/Statistic.h"
void computeDFS(MachineFunction& MF);
- void processPHI(MachineInstr* P);
+ void processBlock(MachineBasicBlock* MBB);
std::vector<DomForestNode*> computeDomForest(std::set<unsigned>& instrs);
+ void breakCriticalEdges(MachineFunction &Fn);
};
}
}
+/// PreorderSorter - a helper class that is used to sort registers
+/// according to the preorder number of their defining blocks
class PreorderSorter {
private:
DenseMap<MachineBasicBlock*, unsigned>& preorder;
}
};
+/// computeDomForest - compute the subforest of the DomTree corresponding
+/// to the defining blocks of the registers in question
std::vector<StrongPHIElimination::DomForestNode*>
StrongPHIElimination::computeDomForest(std::set<unsigned>& regs) {
LiveVariables& LV = getAnalysis<LiveVariables>();
return ret;
}
-void StrongPHIElimination::processPHI(MachineInstr* P) {
+/// isLiveIn - helper method that determines, from a VarInfo, if a register
+/// is live into a block
+bool isLiveIn(LiveVariables::VarInfo& V, MachineBasicBlock* MBB) {
+ if (V.AliveBlocks.test(MBB->getNumber()))
+ return true;
+ if (V.DefInst->getParent() != MBB &&
+ V.UsedBlocks.test(MBB->getNumber()))
+ return true;
+
+ return false;
}
-bool StrongPHIElimination::runOnMachineFunction(MachineFunction &Fn) {
- computeDFS(Fn);
+/// isLiveOut - help method that determines, from a VarInfo, if a register is
+/// live out of a block.
+bool isLiveOut(LiveVariables::VarInfo& V, MachineBasicBlock* MBB) {
+ if (MBB == V.DefInst->getParent() ||
+ V.UsedBlocks.test(MBB->getNumber())) {
+ for (std::vector<MachineInstr*>::iterator I = V.Kills.begin(),
+ E = V.Kills.end(); I != E; ++I)
+ if ((*I)->getParent() == MBB)
+ return false;
+
+ return true;
+ }
- for (MachineFunction::iterator I = Fn.begin(), E = Fn.end(); I != E; ++I) {
- for (MachineBasicBlock::iterator BI = I->begin(), BE = I->end(); BI != BE;
- ++BI) {
- if (BI->getOpcode() == TargetInstrInfo::PHI)
- processPHI(BI);
- else
- break;
+ return false;
+}
+
+/// processBlock - Eliminate PHIs in the given block
+void StrongPHIElimination::processBlock(MachineBasicBlock* MBB) {
+ LiveVariables& LV = getAnalysis<LiveVariables>();
+
+ // Holds names that have been added to a set in any PHI within this block
+ // before the current one.
+ std::set<unsigned> ProcessedNames;
+
+ MachineBasicBlock::iterator P = MBB->begin();
+ while (P->getOpcode() == TargetInstrInfo::PHI) {
+ LiveVariables::VarInfo& PHIInfo = LV.getVarInfo(P->getOperand(0).getReg());
+
+ // Hold the names that are currently in the candidate set.
+ std::set<unsigned> PHIUnion;
+ std::set<MachineBasicBlock*> UnionedBlocks;
+
+ for (int i = P->getNumOperands() - 1; i >= 2; i-=2) {
+ unsigned SrcReg = P->getOperand(i-1).getReg();
+ LiveVariables::VarInfo& SrcInfo = LV.getVarInfo(SrcReg);
+
+ if (isLiveIn(SrcInfo, P->getParent())) {
+ // add a copy from a_i to p in Waiting[From[a_i]]
+ } else if (isLiveOut(PHIInfo, SrcInfo.DefInst->getParent())) {
+ // add a copy to Waiting[From[a_i]]
+ } else if (PHIInfo.DefInst->getOpcode() == TargetInstrInfo::PHI &&
+ isLiveIn(PHIInfo, SrcInfo.DefInst->getParent())) {
+ // add a copy to Waiting[From[a_i]]
+ } else if (ProcessedNames.count(SrcReg)) {
+ // add a copy to Waiting[From[a_i]]
+ } else if (UnionedBlocks.count(SrcInfo.DefInst->getParent())) {
+ // add a copy to Waiting[From[a_i]]
+ } else {
+ PHIUnion.insert(SrcReg);
+ UnionedBlocks.insert(SrcInfo.DefInst->getParent());
+ }
}
+
+ std::vector<StrongPHIElimination::DomForestNode*> DF =
+ computeDomForest(PHIUnion);
+
+ // DO STUFF HERE
+
+ ProcessedNames.insert(PHIUnion.begin(), PHIUnion.end());
+ ++P;
}
+}
+
+/// breakCriticalEdges - Break critical edges coming into blocks with PHI
+/// nodes, preserving dominator and livevariable info.
+void StrongPHIElimination::breakCriticalEdges(MachineFunction &Fn) {
+ typedef std::pair<MachineBasicBlock*, MachineBasicBlock*> MBB_pair;
+
+ MachineDominatorTree& MDT = getAnalysis<MachineDominatorTree>();
+ LiveVariables& LV = getAnalysis<LiveVariables>();
+
+ // Find critical edges
+ std::vector<MBB_pair> criticals;
+ for (MachineFunction::iterator I = Fn.begin(), E = Fn.end(); I != E; ++I)
+ if (!I->empty() &&
+ I->begin()->getOpcode() == TargetInstrInfo::PHI &&
+ I->pred_size() > 1)
+ for (MachineBasicBlock::pred_iterator PI = I->pred_begin(),
+ PE = I->pred_end(); PI != PE; ++PI)
+ if ((*PI)->succ_size() > 1)
+ criticals.push_back(std::make_pair(*PI, I));
+
+ for (std::vector<MBB_pair>::iterator I = criticals.begin(),
+ E = criticals.end(); I != E; ++I) {
+ // Split the edge
+ MachineBasicBlock* new_bb = SplitCriticalMachineEdge(I->first, I->second);
+
+ // Update dominators
+ MDT.splitBlock(I->first);
+
+ // Update livevariables
+ for (unsigned var = 1024; var < Fn.getSSARegMap()->getLastVirtReg(); ++var)
+ if (isLiveOut(LV.getVarInfo(var), I->first))
+ LV.getVarInfo(var).AliveBlocks.set(new_bb->getNumber());
+ }
+}
+
+bool StrongPHIElimination::runOnMachineFunction(MachineFunction &Fn) {
+ breakCriticalEdges(Fn);
+ computeDFS(Fn);
+
+ for (MachineFunction::iterator I = Fn.begin(), E = Fn.end(); I != E; ++I)
+ if (!I->empty() &&
+ I->begin()->getOpcode() == TargetInstrInfo::PHI)
+ processBlock(I);
return false;
}
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