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Machine CSE work in progress. It's doing some CSE now. But implicit def of physical registers are getting in the way. 

llvm-svn: 97664
This commit is contained in:
Evan Cheng 2010-03-03 21:20:05 +00:00
parent f94d68398a
commit b386cd3871
1 changed files with 61 additions and 24 deletions
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85
llvm/lib/CodeGen/MachineCSE.cpp
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@ -25,6 +25,9 @@
using namespace llvm;
STATISTIC(NumCoalesces, "Number of copies coalesced");
STATISTIC(NumCSEs, "Number of common subexpression eliminated");
namespace llvm {
template<> struct DenseMapInfo<MachineInstr*> {
static inline MachineInstr *getEmptyKey() {
@ -93,8 +96,6 @@ namespace {
const TargetInstrInfo *TII;
MachineRegisterInfo *MRI;
MachineDominatorTree *DT;
ScopedHashTable<MachineInstr*, unsigned> VNT;
unsigned CurrVN;
public:
static char ID; // Pass identification
MachineCSE() : MachineFunctionPass(&ID), CurrVN(0) {}
@ -109,6 +110,10 @@ namespace {
}
private:
unsigned CurrVN;
ScopedHashTable<MachineInstr*, unsigned> VNT;
SmallVector<MachineInstr*, 64> Exps;
bool PerformTrivialCoalescing(MachineInstr *MI, MachineBasicBlock *MBB);
bool ProcessBlock(MachineDomTreeNode *Node);
};
@ -125,20 +130,26 @@ bool MachineCSE::PerformTrivialCoalescing(MachineInstr *MI,
bool Changed = false;
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
MachineOperand &MO = MI->getOperand(i);
if (MO.isReg() && MO.isUse()) {
unsigned Reg = MO.getReg();
if (!Reg || TargetRegisterInfo::isPhysicalRegister(Reg))
continue;
MachineInstr *DefMI = MRI->getVRegDef(Reg);
if (DefMI->getParent() == MBB) {
unsigned SrcReg, DstReg, SrcSubIdx, DstSubIdx;
if (TII->isMoveInstr(*DefMI, SrcReg, DstReg, SrcSubIdx, DstSubIdx) &&
TargetRegisterInfo::isVirtualRegister(SrcReg) &&
!SrcSubIdx && !DstSubIdx) {
MO.setReg(SrcReg);
Changed = true;
}
}
if (!MO.isReg() || !MO.isUse())
continue;
unsigned Reg = MO.getReg();
if (!Reg || TargetRegisterInfo::isPhysicalRegister(Reg))
continue;
if (!MRI->hasOneUse(Reg))
// Only coalesce single use copies. This ensure the copy will be
// deleted.
continue;
MachineInstr *DefMI = MRI->getVRegDef(Reg);
if (DefMI->getParent() != MBB)
continue;
unsigned SrcReg, DstReg, SrcSubIdx, DstSubIdx;
if (TII->isMoveInstr(*DefMI, SrcReg, DstReg, SrcSubIdx, DstSubIdx) &&
TargetRegisterInfo::isVirtualRegister(SrcReg) &&
!SrcSubIdx && !DstSubIdx) {
MO.setReg(SrcReg);
DefMI->eraseFromParent();
++NumCoalesces;
Changed = true;
}
}
@ -153,6 +164,8 @@ static bool hasLivePhysRegDefUse(MachineInstr *MI) {
unsigned Reg = MO.getReg();
if (!Reg)
continue;
// FIXME: This is obviously overly conservative. On x86 lots of instructions
// will def EFLAGS and they are not marked dead at this point.
if (TargetRegisterInfo::isPhysicalRegister(Reg) &&
!(MO.isDef() && MO.isDead()))
return true;
@ -165,17 +178,18 @@ bool MachineCSE::ProcessBlock(MachineDomTreeNode *Node) {
ScopedHashTableScope<MachineInstr*, unsigned> VNTS(VNT);
MachineBasicBlock *MBB = Node->getBlock();
for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end(); I != E;
++I) {
for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end(); I != E; ) {
MachineInstr *MI = &*I;
++I;
bool SawStore = false;
if (!MI->isSafeToMove(TII, 0, SawStore))
continue;
// Ignore copies or instructions that read / write physical registers
// (except for dead defs of physical registers).
unsigned SrcReg, DstReg, SrcSubIdx, DstSubIdx;
if (TII->isMoveInstr(*MI, SrcReg, DstReg, SrcSubIdx, DstSubIdx))
continue;
if (TII->isMoveInstr(*MI, SrcReg, DstReg, SrcSubIdx, DstSubIdx) ||
MI->isExtractSubreg() || MI->isInsertSubreg() || MI->isSubregToReg())
continue;
if (hasLivePhysRegDefUse(MI))
continue;
@ -186,10 +200,33 @@ bool MachineCSE::ProcessBlock(MachineDomTreeNode *Node) {
FoundCSE = VNT.count(MI);
}
if (FoundCSE)
DEBUG(dbgs() << "Found a common subexpression: " << *MI);
else
VNT.insert(MI, ++CurrVN);
if (!FoundCSE) {
VNT.insert(MI, CurrVN++);
Exps.push_back(MI);
continue;
}
// Found a common subexpression, eliminate it.
unsigned CSVN = VNT.lookup(MI);
MachineInstr *CSMI = Exps[CSVN];
DEBUG(dbgs() << "Examining: " << *MI);
DEBUG(dbgs() << "*** Found a common subexpression: " << *CSMI);
unsigned NumDefs = MI->getDesc().getNumDefs();
for (unsigned i = 0, e = MI->getNumOperands(); NumDefs && i != e; ++i) {
MachineOperand &MO = MI->getOperand(i);
if (!MO.isReg() || !MO.isDef())
continue;
unsigned OldReg = MO.getReg();
unsigned NewReg = CSMI->getOperand(i).getReg();
assert(OldReg != NewReg &&
TargetRegisterInfo::isVirtualRegister(OldReg) &&
TargetRegisterInfo::isVirtualRegister(NewReg) &&
"Do not CSE physical register defs!");
MRI->replaceRegWith(OldReg, NewReg);
--NumDefs;
}
MI->eraseFromParent();
++NumCSEs;
}
// Recursively call ProcessBlock with childred.