//
//===----------------------------------------------------------------------===//
-#define DEBUG_TYPE "machine-cse"
#include "llvm/CodeGen/Passes.h"
-#include "llvm/CodeGen/MachineDominators.h"
-#include "llvm/CodeGen/MachineInstr.h"
-#include "llvm/CodeGen/MachineRegisterInfo.h"
-#include "llvm/Analysis/AliasAnalysis.h"
-#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/ScopedHashTable.h"
+#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/Statistic.h"
-#include "llvm/Support/CommandLine.h"
+#include "llvm/Analysis/AliasAnalysis.h"
+#include "llvm/CodeGen/MachineDominators.h"
+#include "llvm/CodeGen/MachineInstr.h"
+#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/Support/Debug.h"
-
+#include "llvm/Support/RecyclingAllocator.h"
+#include "llvm/Support/raw_ostream.h"
+#include "llvm/Target/TargetInstrInfo.h"
+#include "llvm/Target/TargetSubtargetInfo.h"
using namespace llvm;
+#define DEBUG_TYPE "machine-cse"
+
STATISTIC(NumCoalesces, "Number of copies coalesced");
STATISTIC(NumCSEs, "Number of common subexpression eliminated");
-STATISTIC(NumPhysCSEs, "Number of phyreg defining common subexpr eliminated");
+STATISTIC(NumPhysCSEs,
+ "Number of physreg referencing common subexpr eliminated");
+STATISTIC(NumCrossBBCSEs,
+ "Number of cross-MBB physreg referencing CS eliminated");
+STATISTIC(NumCommutes, "Number of copies coalesced after commuting");
namespace {
class MachineCSE : public MachineFunctionPass {
MachineRegisterInfo *MRI;
public:
static char ID; // Pass identification
- MachineCSE() : MachineFunctionPass(ID), LookAheadLimit(5), CurrVN(0) {}
+ MachineCSE() : MachineFunctionPass(ID), LookAheadLimit(0), CurrVN(0) {
+ initializeMachineCSEPass(*PassRegistry::getPassRegistry());
+ }
- virtual bool runOnMachineFunction(MachineFunction &MF);
-
- virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+ bool runOnMachineFunction(MachineFunction &MF) override;
+
+ void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.setPreservesCFG();
MachineFunctionPass::getAnalysisUsage(AU);
- AU.addRequired<AliasAnalysis>();
+ AU.addRequired<AAResultsWrapperPass>();
AU.addPreservedID(MachineLoopInfoID);
AU.addRequired<MachineDominatorTree>();
AU.addPreserved<MachineDominatorTree>();
}
- virtual void releaseMemory() {
+ void releaseMemory() override {
ScopeMap.clear();
Exps.clear();
}
private:
- const unsigned LookAheadLimit;
- typedef ScopedHashTableScope<MachineInstr*, unsigned,
- MachineInstrExpressionTrait> ScopeType;
+ unsigned LookAheadLimit;
+ typedef RecyclingAllocator<BumpPtrAllocator,
+ ScopedHashTableVal<MachineInstr*, unsigned> > AllocatorTy;
+ typedef ScopedHashTable<MachineInstr*, unsigned,
+ MachineInstrExpressionTrait, AllocatorTy> ScopedHTType;
+ typedef ScopedHTType::ScopeTy ScopeType;
DenseMap<MachineBasicBlock*, ScopeType*> ScopeMap;
- ScopedHashTable<MachineInstr*, unsigned, MachineInstrExpressionTrait> VNT;
+ ScopedHTType VNT;
SmallVector<MachineInstr*, 64> Exps;
unsigned CurrVN;
- bool PerformTrivialCoalescing(MachineInstr *MI, MachineBasicBlock *MBB);
+ bool PerformTrivialCopyPropagation(MachineInstr *MI,
+ MachineBasicBlock *MBB);
bool isPhysDefTriviallyDead(unsigned Reg,
MachineBasicBlock::const_iterator I,
- MachineBasicBlock::const_iterator E) const ;
- bool hasLivePhysRegDefUse(const MachineInstr *MI,
- const MachineBasicBlock *MBB,
- unsigned &PhysDef) const;
- bool PhysRegDefReaches(MachineInstr *CSMI, MachineInstr *MI,
- unsigned PhysDef) const;
+ MachineBasicBlock::const_iterator E) const;
+ bool hasLivePhysRegDefUses(const MachineInstr *MI,
+ const MachineBasicBlock *MBB,
+ SmallSet<unsigned,8> &PhysRefs,
+ SmallVectorImpl<unsigned> &PhysDefs,
+ bool &PhysUseDef) const;
+ bool PhysRegDefsReach(MachineInstr *CSMI, MachineInstr *MI,
+ SmallSet<unsigned,8> &PhysRefs,
+ SmallVectorImpl<unsigned> &PhysDefs,
+ bool &NonLocal) const;
bool isCSECandidate(MachineInstr *MI);
bool isProfitableToCSE(unsigned CSReg, unsigned Reg,
MachineInstr *CSMI, MachineInstr *MI);
void ExitScope(MachineBasicBlock *MBB);
bool ProcessBlock(MachineBasicBlock *MBB);
void ExitScopeIfDone(MachineDomTreeNode *Node,
- DenseMap<MachineDomTreeNode*, unsigned> &OpenChildren,
- DenseMap<MachineDomTreeNode*, MachineDomTreeNode*> &ParentMap);
+ DenseMap<MachineDomTreeNode*, unsigned> &OpenChildren);
bool PerformCSE(MachineDomTreeNode *Node);
};
} // end anonymous namespace
char MachineCSE::ID = 0;
-INITIALIZE_PASS(MachineCSE, "machine-cse",
- "Machine Common Subexpression Elimination", false, false);
-
-FunctionPass *llvm::createMachineCSEPass() { return new MachineCSE(); }
-
-bool MachineCSE::PerformTrivialCoalescing(MachineInstr *MI,
- MachineBasicBlock *MBB) {
+char &llvm::MachineCSEID = MachineCSE::ID;
+INITIALIZE_PASS_BEGIN(MachineCSE, "machine-cse",
+ "Machine Common Subexpression Elimination", false, false)
+INITIALIZE_PASS_DEPENDENCY(MachineDominatorTree)
+INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)
+INITIALIZE_PASS_END(MachineCSE, "machine-cse",
+ "Machine Common Subexpression Elimination", false, false)
+
+/// The source register of a COPY machine instruction can be propagated to all
+/// its users, and this propagation could increase the probability of finding
+/// common subexpressions. If the COPY has only one user, the COPY itself can
+/// be removed.
+bool MachineCSE::PerformTrivialCopyPropagation(MachineInstr *MI,
+ MachineBasicBlock *MBB) {
bool Changed = false;
- for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
- MachineOperand &MO = MI->getOperand(i);
+ for (MachineOperand &MO : MI->operands()) {
if (!MO.isReg() || !MO.isUse())
continue;
unsigned Reg = MO.getReg();
- if (!Reg || TargetRegisterInfo::isPhysicalRegister(Reg))
- continue;
- if (!MRI->hasOneNonDBGUse(Reg))
- // Only coalesce single use copies. This ensure the copy will be
- // deleted.
+ if (!TargetRegisterInfo::isVirtualRegister(Reg))
continue;
+ bool OnlyOneUse = MRI->hasOneNonDBGUse(Reg);
MachineInstr *DefMI = MRI->getVRegDef(Reg);
- if (DefMI->getParent() != MBB)
- continue;
if (!DefMI->isCopy())
continue;
unsigned SrcReg = DefMI->getOperand(1).getReg();
if (!TargetRegisterInfo::isVirtualRegister(SrcReg))
continue;
- if (DefMI->getOperand(0).getSubReg() || DefMI->getOperand(1).getSubReg())
+ if (DefMI->getOperand(0).getSubReg())
+ continue;
+ // FIXME: We should trivially coalesce subregister copies to expose CSE
+ // opportunities on instructions with truncated operands (see
+ // cse-add-with-overflow.ll). This can be done here as follows:
+ // if (SrcSubReg)
+ // RC = TRI->getMatchingSuperRegClass(MRI->getRegClass(SrcReg), RC,
+ // SrcSubReg);
+ // MO.substVirtReg(SrcReg, SrcSubReg, *TRI);
+ //
+ // The 2-addr pass has been updated to handle coalesced subregs. However,
+ // some machine-specific code still can't handle it.
+ // To handle it properly we also need a way find a constrained subregister
+ // class given a super-reg class and subreg index.
+ if (DefMI->getOperand(1).getSubReg())
continue;
- if (!MRI->constrainRegClass(SrcReg, MRI->getRegClass(Reg)))
+ const TargetRegisterClass *RC = MRI->getRegClass(Reg);
+ if (!MRI->constrainRegClass(SrcReg, RC))
continue;
DEBUG(dbgs() << "Coalescing: " << *DefMI);
DEBUG(dbgs() << "*** to: " << *MI);
+ // Propagate SrcReg of copies to MI.
MO.setReg(SrcReg);
MRI->clearKillFlags(SrcReg);
- DefMI->eraseFromParent();
- ++NumCoalesces;
+ // Coalesce single use copies.
+ if (OnlyOneUse) {
+ DefMI->eraseFromParent();
+ ++NumCoalesces;
+ }
Changed = true;
}
return true;
bool SeenDef = false;
- for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
- const MachineOperand &MO = I->getOperand(i);
+ for (const MachineOperand &MO : I->operands()) {
+ if (MO.isRegMask() && MO.clobbersPhysReg(Reg))
+ SeenDef = true;
if (!MO.isReg() || !MO.getReg())
continue;
if (!TRI->regsOverlap(MO.getReg(), Reg))
SeenDef = true;
}
if (SeenDef)
- // See a def of Reg (or an alias) before encountering any use, it's
+ // See a def of Reg (or an alias) before encountering any use, it's
// trivially dead.
return true;
return false;
}
-/// hasLivePhysRegDefUse - Return true if the specified instruction read / write
+/// hasLivePhysRegDefUses - Return true if the specified instruction read/write
/// physical registers (except for dead defs of physical registers). It also
/// returns the physical register def by reference if it's the only one and the
/// instruction does not uses a physical register.
-bool MachineCSE::hasLivePhysRegDefUse(const MachineInstr *MI,
- const MachineBasicBlock *MBB,
- unsigned &PhysDef) const {
- PhysDef = 0;
- for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
- const MachineOperand &MO = MI->getOperand(i);
- if (!MO.isReg())
+bool MachineCSE::hasLivePhysRegDefUses(const MachineInstr *MI,
+ const MachineBasicBlock *MBB,
+ SmallSet<unsigned,8> &PhysRefs,
+ SmallVectorImpl<unsigned> &PhysDefs,
+ bool &PhysUseDef) const{
+ // First, add all uses to PhysRefs.
+ for (const MachineOperand &MO : MI->operands()) {
+ if (!MO.isReg() || MO.isDef())
continue;
unsigned Reg = MO.getReg();
if (!Reg)
continue;
if (TargetRegisterInfo::isVirtualRegister(Reg))
continue;
- if (MO.isUse()) {
- // Can't touch anything to read a physical register.
- PhysDef = 0;
- return true;
- }
- if (MO.isDead())
- // If the def is dead, it's ok.
+ // Reading constant physregs is ok.
+ if (!MRI->isConstantPhysReg(Reg, *MBB->getParent()))
+ for (MCRegAliasIterator AI(Reg, TRI, true); AI.isValid(); ++AI)
+ PhysRefs.insert(*AI);
+ }
+
+ // Next, collect all defs into PhysDefs. If any is already in PhysRefs
+ // (which currently contains only uses), set the PhysUseDef flag.
+ PhysUseDef = false;
+ MachineBasicBlock::const_iterator I = MI; I = std::next(I);
+ for (const MachineOperand &MO : MI->operands()) {
+ if (!MO.isReg() || !MO.isDef())
+ continue;
+ unsigned Reg = MO.getReg();
+ if (!Reg)
continue;
- // Ok, this is a physical register def that's not marked "dead". That's
+ if (TargetRegisterInfo::isVirtualRegister(Reg))
+ continue;
+ // Check against PhysRefs even if the def is "dead".
+ if (PhysRefs.count(Reg))
+ PhysUseDef = true;
+ // If the def is dead, it's ok. But the def may not marked "dead". That's
// common since this pass is run before livevariables. We can scan
// forward a few instructions and check if it is obviously dead.
- if (PhysDef) {
- // Multiple physical register defs. These are rare, forget about it.
- PhysDef = 0;
- return true;
- }
- PhysDef = Reg;
+ if (!MO.isDead() && !isPhysDefTriviallyDead(Reg, I, MBB->end()))
+ PhysDefs.push_back(Reg);
}
- if (PhysDef) {
- MachineBasicBlock::const_iterator I = MI; I = llvm::next(I);
- if (!isPhysDefTriviallyDead(PhysDef, I, MBB->end()))
- return true;
- }
- return false;
+ // Finally, add all defs to PhysRefs as well.
+ for (unsigned i = 0, e = PhysDefs.size(); i != e; ++i)
+ for (MCRegAliasIterator AI(PhysDefs[i], TRI, true); AI.isValid(); ++AI)
+ PhysRefs.insert(*AI);
+
+ return !PhysRefs.empty();
}
-bool MachineCSE::PhysRegDefReaches(MachineInstr *CSMI, MachineInstr *MI,
- unsigned PhysDef) const {
+bool MachineCSE::PhysRegDefsReach(MachineInstr *CSMI, MachineInstr *MI,
+ SmallSet<unsigned,8> &PhysRefs,
+ SmallVectorImpl<unsigned> &PhysDefs,
+ bool &NonLocal) const {
// 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);
+ // not in the same basic block as the given instruction. The only exception
+ // is if the common subexpression is in the sole predecessor block.
+ const MachineBasicBlock *MBB = MI->getParent();
+ const MachineBasicBlock *CSMBB = CSMI->getParent();
+
+ bool CrossMBB = false;
+ if (CSMBB != MBB) {
+ if (MBB->pred_size() != 1 || *MBB->pred_begin() != CSMBB)
+ return false;
+
+ for (unsigned i = 0, e = PhysDefs.size(); i != e; ++i) {
+ if (MRI->isAllocatable(PhysDefs[i]) || MRI->isReserved(PhysDefs[i]))
+ // Avoid extending live range of physical registers if they are
+ //allocatable or reserved.
+ return false;
+ }
+ CrossMBB = true;
+ }
+ MachineBasicBlock::const_iterator I = CSMI; I = std::next(I);
MachineBasicBlock::const_iterator E = MI;
+ MachineBasicBlock::const_iterator EE = CSMBB->end();
unsigned LookAheadLeft = LookAheadLimit;
while (LookAheadLeft) {
// Skip over dbg_value's.
- while (I != E && I->isDebugValue())
+ while (I != E && I != EE && I->isDebugValue())
++I;
+ if (I == EE) {
+ assert(CrossMBB && "Reaching end-of-MBB without finding MI?");
+ (void)CrossMBB;
+ CrossMBB = false;
+ NonLocal = true;
+ I = MBB->begin();
+ EE = MBB->end();
+ continue;
+ }
+
if (I == E)
return true;
- if (I->modifiesRegister(PhysDef, TRI))
- return false;
+
+ for (const MachineOperand &MO : I->operands()) {
+ // RegMasks go on instructions like calls that clobber lots of physregs.
+ // Don't attempt to CSE across such an instruction.
+ if (MO.isRegMask())
+ return false;
+ if (!MO.isReg() || !MO.isDef())
+ continue;
+ unsigned MOReg = MO.getReg();
+ if (TargetRegisterInfo::isVirtualRegister(MOReg))
+ continue;
+ if (PhysRefs.count(MOReg))
+ return false;
+ }
--LookAheadLeft;
++I;
}
bool MachineCSE::isCSECandidate(MachineInstr *MI) {
- if (MI->isLabel() || MI->isPHI() || MI->isImplicitDef() ||
- MI->isKill() || MI->isInlineAsm() || MI->isDebugValue())
+ if (MI->isPosition() || MI->isPHI() || MI->isImplicitDef() || MI->isKill() ||
+ MI->isInlineAsm() || MI->isDebugValue())
return false;
// Ignore copies.
return false;
// Ignore stuff that we obviously can't move.
- const TargetInstrDesc &TID = MI->getDesc();
- if (TID.mayStore() || TID.isCall() || TID.isTerminator() ||
- TID.hasUnmodeledSideEffects())
+ if (MI->mayStore() || MI->isCall() || MI->isTerminator() ||
+ MI->hasUnmodeledSideEffects())
return false;
- if (TID.mayLoad()) {
+ if (MI->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.
MachineInstr *CSMI, MachineInstr *MI) {
// FIXME: Heuristics that works around the lack the live range splitting.
- // Heuristics #1: Don't cse "cheap" computating if the def is not local or in an
- // immediate predecessor. We don't want to increase register pressure and end up
- // causing other computation to be spilled.
- if (MI->getDesc().isAsCheapAsAMove()) {
+ // If CSReg is used at all uses of Reg, CSE should not increase register
+ // pressure of CSReg.
+ bool MayIncreasePressure = true;
+ if (TargetRegisterInfo::isVirtualRegister(CSReg) &&
+ TargetRegisterInfo::isVirtualRegister(Reg)) {
+ MayIncreasePressure = false;
+ SmallPtrSet<MachineInstr*, 8> CSUses;
+ for (MachineInstr &MI : MRI->use_nodbg_instructions(CSReg)) {
+ CSUses.insert(&MI);
+ }
+ for (MachineInstr &MI : MRI->use_nodbg_instructions(Reg)) {
+ if (!CSUses.count(&MI)) {
+ MayIncreasePressure = true;
+ break;
+ }
+ }
+ }
+ if (!MayIncreasePressure) return true;
+
+ // Heuristics #1: Don't CSE "cheap" computation if the def is not local or in
+ // an immediate predecessor. We don't want to increase register pressure and
+ // end up causing other computation to be spilled.
+ if (TII->isAsCheapAsAMove(MI)) {
MachineBasicBlock *CSBB = CSMI->getParent();
MachineBasicBlock *BB = MI->getParent();
- if (CSBB != BB &&
- find(CSBB->succ_begin(), CSBB->succ_end(), BB) == CSBB->succ_end())
+ if (CSBB != BB && !CSBB->isSuccessor(BB))
return false;
}
// Heuristics #2: If the expression doesn't not use a vr and the only use
// of the redundant computation are copies, do not cse.
bool HasVRegUse = false;
- for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
- const MachineOperand &MO = MI->getOperand(i);
- if (MO.isReg() && MO.isUse() && MO.getReg() &&
+ for (const MachineOperand &MO : MI->operands()) {
+ if (MO.isReg() && MO.isUse() &&
TargetRegisterInfo::isVirtualRegister(MO.getReg())) {
HasVRegUse = true;
break;
}
if (!HasVRegUse) {
bool HasNonCopyUse = false;
- for (MachineRegisterInfo::use_nodbg_iterator I = MRI->use_nodbg_begin(Reg),
- E = MRI->use_nodbg_end(); I != E; ++I) {
- MachineInstr *Use = &*I;
+ for (MachineInstr &MI : MRI->use_nodbg_instructions(Reg)) {
// Ignore copies.
- if (!Use->isCopyLike()) {
+ if (!MI.isCopyLike()) {
HasNonCopyUse = true;
break;
}
// it unless the defined value is already used in the BB of the new use.
bool HasPHI = false;
SmallPtrSet<MachineBasicBlock*, 4> CSBBs;
- for (MachineRegisterInfo::use_nodbg_iterator I = MRI->use_nodbg_begin(CSReg),
- E = MRI->use_nodbg_end(); I != E; ++I) {
- MachineInstr *Use = &*I;
- HasPHI |= Use->isPHI();
- CSBBs.insert(Use->getParent());
+ for (MachineInstr &MI : MRI->use_nodbg_instructions(CSReg)) {
+ HasPHI |= MI.isPHI();
+ CSBBs.insert(MI.getParent());
}
if (!HasPHI)
DEBUG(dbgs() << "Exiting: " << MBB->getName() << '\n');
DenseMap<MachineBasicBlock*, ScopeType*>::iterator SI = ScopeMap.find(MBB);
assert(SI != ScopeMap.end());
- ScopeMap.erase(SI);
delete SI->second;
+ ScopeMap.erase(SI);
}
bool MachineCSE::ProcessBlock(MachineBasicBlock *MBB) {
bool Changed = false;
SmallVector<std::pair<unsigned, unsigned>, 8> CSEPairs;
+ SmallVector<unsigned, 2> ImplicitDefsToUpdate;
+ SmallVector<unsigned, 2> ImplicitDefs;
for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end(); I != E; ) {
MachineInstr *MI = &*I;
++I;
if (!isCSECandidate(MI))
continue;
- bool DefPhys = false;
bool FoundCSE = VNT.count(MI);
if (!FoundCSE) {
- // Look for trivial copy coalescing opportunities.
- if (PerformTrivialCoalescing(MI, MBB)) {
+ // Using trivial copy propagation to find more CSE opportunities.
+ if (PerformTrivialCopyPropagation(MI, MBB)) {
+ Changed = true;
+
// After coalescing MI itself may become a copy.
if (MI->isCopyLike())
continue;
+
+ // Try again to see if CSE is possible.
FoundCSE = VNT.count(MI);
}
}
- // FIXME: commute commutable instructions?
- // If the instruction defines a physical register and the value *may* be
+ // Commute commutable instructions.
+ bool Commuted = false;
+ if (!FoundCSE && MI->isCommutable()) {
+ MachineInstr *NewMI = TII->commuteInstruction(MI);
+ if (NewMI) {
+ Commuted = true;
+ FoundCSE = VNT.count(NewMI);
+ if (NewMI != MI) {
+ // New instruction. It doesn't need to be kept.
+ NewMI->eraseFromParent();
+ Changed = true;
+ } else if (!FoundCSE)
+ // MI was changed but it didn't help, commute it back!
+ (void)TII->commuteInstruction(MI);
+ }
+ }
+
+ // If the instruction defines physical registers and the values *may* be
// used, then it's not safe to replace it with a common subexpression.
- unsigned PhysDef = 0;
- if (FoundCSE && hasLivePhysRegDefUse(MI, MBB, PhysDef)) {
+ // It's also not safe if the instruction uses physical registers.
+ bool CrossMBBPhysDef = false;
+ SmallSet<unsigned, 8> PhysRefs;
+ SmallVector<unsigned, 2> PhysDefs;
+ bool PhysUseDef = false;
+ if (FoundCSE && hasLivePhysRegDefUses(MI, MBB, PhysRefs,
+ PhysDefs, PhysUseDef)) {
FoundCSE = false;
- // ... Unless the CS is local and it also defines the physical register
- // which is not clobbered in between.
- if (PhysDef) {
+ // ... Unless the CS is local or is in the sole predecessor block
+ // and it also defines the physical register which is not clobbered
+ // in between and the physical register uses were not clobbered.
+ // This can never be the case if the instruction both uses and
+ // defines the same physical register, which was detected above.
+ if (!PhysUseDef) {
unsigned CSVN = VNT.lookup(MI);
MachineInstr *CSMI = Exps[CSVN];
- if (PhysRegDefReaches(CSMI, MI, PhysDef)) {
+ if (PhysRegDefsReach(CSMI, MI, PhysRefs, PhysDefs, CrossMBBPhysDef))
FoundCSE = true;
- DefPhys = true;
- }
}
}
// Check if it's profitable to perform this CSE.
bool DoCSE = true;
- unsigned NumDefs = MI->getDesc().getNumDefs();
+ unsigned NumDefs = MI->getDesc().getNumDefs() +
+ MI->getDesc().getNumImplicitDefs();
+
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();
- if (OldReg == NewReg)
+
+ // Go through implicit defs of CSMI and MI, if a def is not dead at MI,
+ // we should make sure it is not dead at CSMI.
+ if (MO.isImplicit() && !MO.isDead() && CSMI->getOperand(i).isDead())
+ ImplicitDefsToUpdate.push_back(i);
+
+ // Keep track of implicit defs of CSMI and MI, to clear possibly
+ // made-redundant kill flags.
+ if (MO.isImplicit() && !MO.isDead() && OldReg == NewReg)
+ ImplicitDefs.push_back(OldReg);
+
+ if (OldReg == NewReg) {
+ --NumDefs;
continue;
+ }
+
assert(TargetRegisterInfo::isVirtualRegister(OldReg) &&
TargetRegisterInfo::isVirtualRegister(NewReg) &&
"Do not CSE physical register defs!");
+
if (!isProfitableToCSE(NewReg, OldReg, CSMI, MI)) {
+ DEBUG(dbgs() << "*** Not profitable, avoid CSE!\n");
+ 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)) {
+ DEBUG(dbgs() << "*** Not the same register class, avoid CSE!\n");
DoCSE = false;
break;
}
+
CSEPairs.push_back(std::make_pair(OldReg, NewReg));
--NumDefs;
}
// Actually perform the elimination.
if (DoCSE) {
- for (unsigned i = 0, e = CSEPairs.size(); i != e; ++i) {
- MRI->replaceRegWith(CSEPairs[i].first, CSEPairs[i].second);
- MRI->clearKillFlags(CSEPairs[i].second);
+ for (std::pair<unsigned, unsigned> &CSEPair : CSEPairs) {
+ unsigned OldReg = CSEPair.first;
+ unsigned NewReg = CSEPair.second;
+ // OldReg may have been unused but is used now, clear the Dead flag
+ MachineInstr *Def = MRI->getUniqueVRegDef(NewReg);
+ assert(Def != nullptr && "CSEd register has no unique definition?");
+ Def->clearRegisterDeads(NewReg);
+ // Replace with NewReg and clear kill flags which may be wrong now.
+ MRI->replaceRegWith(OldReg, NewReg);
+ MRI->clearKillFlags(NewReg);
+ }
+
+ // Go through implicit defs of CSMI and MI, if a def is not dead at MI,
+ // we should make sure it is not dead at CSMI.
+ for (unsigned ImplicitDefToUpdate : ImplicitDefsToUpdate)
+ CSMI->getOperand(ImplicitDefToUpdate).setIsDead(false);
+
+ // Go through implicit defs of CSMI and MI, and clear the kill flags on
+ // their uses in all the instructions between CSMI and MI.
+ // We might have made some of the kill flags redundant, consider:
+ // subs ... %NZCV<imp-def> <- CSMI
+ // csinc ... %NZCV<imp-use,kill> <- this kill flag isn't valid anymore
+ // subs ... %NZCV<imp-def> <- MI, to be eliminated
+ // csinc ... %NZCV<imp-use,kill>
+ // Since we eliminated MI, and reused a register imp-def'd by CSMI
+ // (here %NZCV), that register, if it was killed before MI, should have
+ // that kill flag removed, because it's lifetime was extended.
+ if (CSMI->getParent() == MI->getParent()) {
+ for (MachineBasicBlock::iterator II = CSMI, IE = MI; II != IE; ++II)
+ for (auto ImplicitDef : ImplicitDefs)
+ if (MachineOperand *MO = II->findRegisterUseOperand(
+ ImplicitDef, /*isKill=*/true, TRI))
+ MO->setIsKill(false);
+ } else {
+ // If the instructions aren't in the same BB, bail out and clear the
+ // kill flag on all uses of the imp-def'd register.
+ for (auto ImplicitDef : ImplicitDefs)
+ MRI->clearKillFlags(ImplicitDef);
}
+
+ if (CrossMBBPhysDef) {
+ // Add physical register defs now coming in from a predecessor to MBB
+ // livein list.
+ while (!PhysDefs.empty()) {
+ unsigned LiveIn = PhysDefs.pop_back_val();
+ if (!MBB->isLiveIn(LiveIn))
+ MBB->addLiveIn(LiveIn);
+ }
+ ++NumCrossBBCSEs;
+ }
+
MI->eraseFromParent();
++NumCSEs;
- if (DefPhys)
+ if (!PhysRefs.empty())
++NumPhysCSEs;
+ if (Commuted)
+ ++NumCommutes;
+ Changed = true;
} else {
- DEBUG(dbgs() << "*** Not profitable, avoid CSE!\n");
VNT.insert(MI, CurrVN++);
Exps.push_back(MI);
}
CSEPairs.clear();
+ ImplicitDefsToUpdate.clear();
+ ImplicitDefs.clear();
}
return Changed;
/// up the dominator tree to destroy ancestors which are now done.
void
MachineCSE::ExitScopeIfDone(MachineDomTreeNode *Node,
- DenseMap<MachineDomTreeNode*, unsigned> &OpenChildren,
- DenseMap<MachineDomTreeNode*, MachineDomTreeNode*> &ParentMap) {
+ DenseMap<MachineDomTreeNode*, unsigned> &OpenChildren) {
if (OpenChildren[Node])
return;
ExitScope(Node->getBlock());
// Now traverse upwards to pop ancestors whose offsprings are all done.
- while (MachineDomTreeNode *Parent = ParentMap[Node]) {
+ while (MachineDomTreeNode *Parent = Node->getIDom()) {
unsigned Left = --OpenChildren[Parent];
if (Left != 0)
break;
bool MachineCSE::PerformCSE(MachineDomTreeNode *Node) {
SmallVector<MachineDomTreeNode*, 32> Scopes;
SmallVector<MachineDomTreeNode*, 8> WorkList;
- DenseMap<MachineDomTreeNode*, MachineDomTreeNode*> ParentMap;
DenseMap<MachineDomTreeNode*, unsigned> OpenChildren;
CurrVN = 0;
Node = WorkList.pop_back_val();
Scopes.push_back(Node);
const std::vector<MachineDomTreeNode*> &Children = Node->getChildren();
- unsigned NumChildren = Children.size();
- OpenChildren[Node] = NumChildren;
- for (unsigned i = 0; i != NumChildren; ++i) {
- MachineDomTreeNode *Child = Children[i];
- ParentMap[Child] = Node;
+ OpenChildren[Node] = Children.size();
+ for (MachineDomTreeNode *Child : Children)
WorkList.push_back(Child);
- }
} while (!WorkList.empty());
// Now perform CSE.
bool Changed = false;
- for (unsigned i = 0, e = Scopes.size(); i != e; ++i) {
- MachineDomTreeNode *Node = Scopes[i];
+ for (MachineDomTreeNode *Node : Scopes) {
MachineBasicBlock *MBB = Node->getBlock();
EnterScope(MBB);
Changed |= ProcessBlock(MBB);
// If it's a leaf node, it's done. Traverse upwards to pop ancestors.
- ExitScopeIfDone(Node, OpenChildren, ParentMap);
+ ExitScopeIfDone(Node, OpenChildren);
}
return Changed;
}
bool MachineCSE::runOnMachineFunction(MachineFunction &MF) {
- TII = MF.getTarget().getInstrInfo();
- TRI = MF.getTarget().getRegisterInfo();
+ if (skipOptnoneFunction(*MF.getFunction()))
+ return false;
+
+ TII = MF.getSubtarget().getInstrInfo();
+ TRI = MF.getSubtarget().getRegisterInfo();
MRI = &MF.getRegInfo();
- AA = &getAnalysis<AliasAnalysis>();
+ AA = &getAnalysis<AAResultsWrapperPass>().getAAResults();
DT = &getAnalysis<MachineDominatorTree>();
+ LookAheadLimit = TII->getMachineCSELookAheadLimit();
return PerformCSE(DT->getRootNode());
}
projects / oota-llvm.git / blobdiff