X-Git-Url: http://plrg.eecs.uci.edu/git/?p=oota-llvm.git;a=blobdiff_plain;f=lib%2FCodeGen%2FMachineCSE.cpp;h=7eda8c129dc47dccb9b87ece8c0aa21d1ac58bce;hp=5d79e96097e31bfb1ebd810e1e348898dbc08364;hb=f6fb7ed53c786228445fc55e8d495ccead59b9ae;hpb=baf717a08a0bc8cb0a7931ea3ce51d063a8fe6f0 diff --git a/lib/CodeGen/MachineCSE.cpp b/lib/CodeGen/MachineCSE.cpp index 5d79e96097e..7eda8c129dc 100644 --- a/lib/CodeGen/MachineCSE.cpp +++ b/lib/CodeGen/MachineCSE.cpp @@ -33,8 +33,6 @@ STATISTIC(NumCoalesces, "Number of copies coalesced"); STATISTIC(NumCSEs, "Number of common subexpression eliminated"); STATISTIC(NumPhysCSEs, "Number of physreg referencing common subexpr eliminated"); -STATISTIC(NumCrossBlockPhysCSEs, - "Number of physreg common subexprs cross-block eliminated"); STATISTIC(NumCommutes, "Number of copies coalesced after commuting"); namespace { @@ -84,8 +82,7 @@ namespace { MachineBasicBlock::const_iterator E) const ; bool hasLivePhysRegDefUses(const MachineInstr *MI, const MachineBasicBlock *MBB, - SmallSet &PhysRefs, - SmallVector &PhysDefs) const; + SmallSet &PhysRefs) const; bool PhysRegDefsReach(MachineInstr *CSMI, MachineInstr *MI, SmallSet &PhysRefs) const; bool isCSECandidate(MachineInstr *MI); @@ -192,8 +189,7 @@ MachineCSE::isPhysDefTriviallyDead(unsigned Reg, /// instruction does not uses a physical register. bool MachineCSE::hasLivePhysRegDefUses(const MachineInstr *MI, const MachineBasicBlock *MBB, - SmallSet &PhysRefs, - SmallVector &PhysDefs) const{ + SmallSet &PhysRefs) const { MachineBasicBlock::const_iterator I = MI; I = llvm::next(I); for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) { const MachineOperand &MO = MI->getOperand(i); @@ -210,7 +206,6 @@ bool MachineCSE::hasLivePhysRegDefUses(const MachineInstr *MI, if (MO.isDef() && (MO.isDead() || isPhysDefTriviallyDead(Reg, I, MBB->end()))) continue; - PhysDefs.push_back(Reg); PhysRefs.insert(Reg); for (const unsigned *Alias = TRI->getAliasSet(Reg); *Alias; ++Alias) PhysRefs.insert(*Alias); @@ -221,43 +216,35 @@ bool MachineCSE::hasLivePhysRegDefUses(const MachineInstr *MI, bool MachineCSE::PhysRegDefsReach(MachineInstr *CSMI, MachineInstr *MI, SmallSet &PhysRefs) const { - // Look backward from MI to find CSMI. + // For now conservatively returns false if the common subexpression is + // not in the same basic block as the given instruction. + MachineBasicBlock *MBB = MI->getParent(); + if (CSMI->getParent() != MBB) + return false; + MachineBasicBlock::const_iterator I = CSMI; I = llvm::next(I); + MachineBasicBlock::const_iterator E = MI; unsigned LookAheadLeft = LookAheadLimit; - MachineBasicBlock *CurBB = MI->getParent(); - MachineBasicBlock::const_reverse_iterator I(MI); - MachineBasicBlock::const_reverse_iterator E(CurBB->rend()); while (LookAheadLeft) { - while (LookAheadLeft && I != E) { - // Skip over dbg_value's. - while (I != E && I->isDebugValue()) - ++I; - - if (I == E) break; - - if (&*I == CSMI) - return true; + // Skip over dbg_value's. + while (I != E && I->isDebugValue()) + ++I; - for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) { - const MachineOperand &MO = I->getOperand(i); - if (!MO.isReg() || !MO.isDef()) - continue; - unsigned MOReg = MO.getReg(); - if (TargetRegisterInfo::isVirtualRegister(MOReg)) - continue; - if (PhysRefs.count(MOReg)) - return false; - } + if (I == E) + return true; - --LookAheadLeft; - ++I; + for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) { + const MachineOperand &MO = I->getOperand(i); + if (!MO.isReg() || !MO.isDef()) + continue; + unsigned MOReg = MO.getReg(); + if (TargetRegisterInfo::isVirtualRegister(MOReg)) + continue; + if (PhysRefs.count(MOReg)) + return false; } - // Go back another BB; for now, only go back at most one BB. - MachineBasicBlock *CSBB = CSMI->getParent(); - if (!CSBB->isSuccessor(CurBB) || CurBB->pred_size() != 1) - return false; - CurBB = CSBB; - I = CSBB->rbegin(); - E = CSBB->rend(); + + --LookAheadLeft; + ++I; } return false; @@ -273,12 +260,12 @@ bool MachineCSE::isCSECandidate(MachineInstr *MI) { return false; // Ignore stuff that we obviously can't move. - const TargetInstrDesc &TID = MI->getDesc(); - if (TID.mayStore() || TID.isCall() || TID.isTerminator() || + const MCInstrDesc &MCID = MI->getDesc(); + if (MCID.mayStore() || MCID.isCall() || MCID.isTerminator() || MI->hasUnmodeledSideEffects()) return false; - if (TID.mayLoad()) { + if (MCID.mayLoad()) { // Okay, this instruction does a load. As a refinement, we allow the target // to decide whether the loaded value is actually a constant. If so, we can // actually use it as a load. @@ -408,8 +395,7 @@ bool MachineCSE::ProcessBlock(MachineBasicBlock *MBB) { // used, then it's not safe to replace it with a common subexpression. // It's also not safe if the instruction uses physical registers. SmallSet PhysRefs; - SmallVector DirectPhysRefs; - if (FoundCSE && hasLivePhysRegDefUses(MI, MBB, PhysRefs, DirectPhysRefs)) { + if (FoundCSE && hasLivePhysRegDefUses(MI, MBB, PhysRefs)) { FoundCSE = false; // ... Unless the CS is local and it also defines the physical register @@ -444,13 +430,24 @@ bool MachineCSE::ProcessBlock(MachineBasicBlock *MBB) { unsigned NewReg = CSMI->getOperand(i).getReg(); if (OldReg == NewReg) continue; + assert(TargetRegisterInfo::isVirtualRegister(OldReg) && TargetRegisterInfo::isVirtualRegister(NewReg) && "Do not CSE physical register defs!"); + if (!isProfitableToCSE(NewReg, OldReg, CSMI, MI)) { DoCSE = false; break; } + + // Don't perform CSE if the result of the old instruction cannot exist + // within the register class of the new instruction. + const TargetRegisterClass *OldRC = MRI->getRegClass(OldReg); + if (!MRI->constrainRegClass(NewReg, OldRC)) { + DoCSE = false; + break; + } + CSEPairs.push_back(std::make_pair(OldReg, NewReg)); --NumDefs; } @@ -462,14 +459,6 @@ bool MachineCSE::ProcessBlock(MachineBasicBlock *MBB) { MRI->clearKillFlags(CSEPairs[i].second); } MI->eraseFromParent(); - if (!DirectPhysRefs.empty() && CSMI->getParent() != MBB) { - assert(CSMI->getParent()->isSuccessor(MBB)); - ++NumCrossBlockPhysCSEs; - SmallVector::iterator PI = DirectPhysRefs.begin(), - PE = DirectPhysRefs.end(); - for (; PI != PE; ++PI) - MBB->addLiveIn(*PI); - } ++NumCSEs; if (!PhysRefs.empty()) ++NumPhysCSEs;