#include "llvm/ADT/Statistic.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/RecyclingAllocator.h"
-
using namespace llvm;
STATISTIC(NumCoalesces, "Number of copies coalesced");
STATISTIC(NumCSEs, "Number of common subexpression 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 {
}
virtual bool runOnMachineFunction(MachineFunction &MF);
-
+
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesCFG();
MachineFunctionPass::getAnalysisUsage(AU);
MachineBasicBlock::const_iterator E) const ;
bool hasLivePhysRegDefUses(const MachineInstr *MI,
const MachineBasicBlock *MBB,
- SmallSet<unsigned,8> &PhysRefs) const;
+ SmallSet<unsigned,8> &PhysRefs,
+ SmallVector<unsigned,2> &PhysDefs) const;
bool PhysRegDefsReach(MachineInstr *CSMI, MachineInstr *MI,
- SmallSet<unsigned,8> &PhysRefs) const;
+ SmallSet<unsigned,8> &PhysRefs,
+ SmallVector<unsigned,2> &PhysDefs,
+ bool &NonLocal) const;
bool isCSECandidate(MachineInstr *MI);
bool isProfitableToCSE(unsigned CSReg, unsigned Reg,
MachineInstr *CSMI, MachineInstr *MI);
} // end anonymous namespace
char MachineCSE::ID = 0;
+char &llvm::MachineCSEID = MachineCSE::ID;
INITIALIZE_PASS_BEGIN(MachineCSE, "machine-cse",
"Machine Common Subexpression Elimination", false, false)
INITIALIZE_PASS_DEPENDENCY(MachineDominatorTree)
INITIALIZE_PASS_END(MachineCSE, "machine-cse",
"Machine Common Subexpression Elimination", false, false)
-FunctionPass *llvm::createMachineCSEPass() { return new MachineCSE(); }
-
bool MachineCSE::PerformTrivialCoalescing(MachineInstr *MI,
MachineBasicBlock *MBB) {
bool Changed = false;
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;
/// instruction does not uses a physical register.
bool MachineCSE::hasLivePhysRegDefUses(const MachineInstr *MI,
const MachineBasicBlock *MBB,
- SmallSet<unsigned,8> &PhysRefs) const {
+ SmallSet<unsigned,8> &PhysRefs,
+ SmallVector<unsigned,2> &PhysDefs) 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);
(MO.isDead() || isPhysDefTriviallyDead(Reg, I, MBB->end())))
continue;
PhysRefs.insert(Reg);
+ if (MO.isDef())
+ PhysDefs.push_back(Reg);
for (const unsigned *Alias = TRI->getAliasSet(Reg); *Alias; ++Alias)
PhysRefs.insert(*Alias);
}
}
bool MachineCSE::PhysRegDefsReach(MachineInstr *CSMI, MachineInstr *MI,
- SmallSet<unsigned,8> &PhysRefs) const {
+ SmallSet<unsigned,8> &PhysRefs,
+ SmallVector<unsigned,2> &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;
+ // 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 (TRI->isInAllocatableClass(PhysDefs[i]))
+ // Avoid extending live range of physical registers unless
+ // they are unallocatable.
+ return false;
+ }
+ CrossMBB = true;
+ }
MachineBasicBlock::const_iterator I = CSMI; I = llvm::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 the instruction defines physical registers and the values *may* be
// used, then it's not safe to replace it with a common subexpression.
// It's also not safe if the instruction uses physical registers.
+ bool CrossMBBPhysDef = false;
SmallSet<unsigned,8> PhysRefs;
- if (FoundCSE && hasLivePhysRegDefUses(MI, MBB, PhysRefs)) {
+ SmallVector<unsigned, 2> PhysDefs;
+ if (FoundCSE && hasLivePhysRegDefUses(MI, MBB, PhysRefs, PhysDefs)) {
FoundCSE = false;
- // ... Unless the CS is local and it also defines the physical register
- // which is not clobbered in between and the physical register uses
- // were not clobbered.
+ // ... 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.
unsigned CSVN = VNT.lookup(MI);
MachineInstr *CSMI = Exps[CSVN];
- if (PhysRegDefsReach(CSMI, MI, PhysRefs))
+ if (PhysRegDefsReach(CSMI, MI, PhysRefs, PhysDefs, CrossMBBPhysDef))
FoundCSE = true;
}
MRI->replaceRegWith(CSEPairs[i].first, CSEPairs[i].second);
MRI->clearKillFlags(CSEPairs[i].second);
}
+
+ 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 (!PhysRefs.empty())