#define DEBUG_TYPE "machine-licm"
#include "llvm/CodeGen/Passes.h"
+#include "llvm/CodeGen/MachineConstantPool.h"
#include "llvm/CodeGen/MachineDominators.h"
#include "llvm/CodeGen/MachineLoopInfo.h"
#include "llvm/CodeGen/MachineMemOperand.h"
namespace {
class MachineLICM : public MachineFunctionPass {
+ MachineConstantPool *MCP;
const TargetMachine *TM;
const TargetInstrInfo *TII;
const TargetRegisterInfo *TRI;
///
void HoistRegion(MachineDomTreeNode *N);
+ /// isLoadFromConstantMemory - Return true if the given instruction is a
+ /// load from constant memory.
+ bool isLoadFromConstantMemory(MachineInstr *MI);
+
/// ExtractHoistableLoad - Unfold a load from the given machineinstr if
/// the load itself could be hoisted. Return the unfolded and hoistable
/// load, or null if the load couldn't be unfolded or if it wouldn't
/// be hoistable.
MachineInstr *ExtractHoistableLoad(MachineInstr *MI);
+ /// LookForDuplicate - Find an instruction amount PrevMIs that is a
+ /// duplicate of MI. Return this instruction if it's found.
+ const MachineInstr *LookForDuplicate(const MachineInstr *MI,
+ std::vector<const MachineInstr*> &PrevMIs);
+
/// EliminateCSE - Given a LICM'ed instruction, look for an instruction on
/// the preheader that compute the same value. If it's found, do a RAU on
/// with the definition of the existing instruction rather than hoisting
DEBUG(errs() << "******** Machine LICM ********\n");
Changed = FirstInLoop = false;
+ MCP = MF.getConstantPool();
TM = &MF.getTarget();
TII = TM->getInstrInfo();
TRI = TM->getRegisterInfo();
// to decide whether the loaded value is actually a constant. If so, we can
// actually use it as a load.
if (!I.isInvariantLoad(AA))
- // FIXME: we should be able to sink loads with no other side effects if
- // there is nothing that can change memory from here until the end of
- // block. This is a trivial form of alias analysis.
+ // FIXME: we should be able to hoist loads with no other side effects if
+ // there are no other instructions which can change memory in this loop.
+ // This is a trivial form of alias analysis.
return false;
}
return false;
}
+/// isLoadFromConstantMemory - Return true if the given instruction is a
+/// load from constant memory. Machine LICM will hoist these even if they are
+/// not re-materializable.
+bool MachineLICM::isLoadFromConstantMemory(MachineInstr *MI) {
+ if (!MI->getDesc().mayLoad()) return false;
+ if (!MI->hasOneMemOperand()) return false;
+ MachineMemOperand *MMO = *MI->memoperands_begin();
+ if (MMO->isVolatile()) return false;
+ if (!MMO->getValue()) return false;
+ const PseudoSourceValue *PSV = dyn_cast<PseudoSourceValue>(MMO->getValue());
+ if (PSV) {
+ MachineFunction &MF = *MI->getParent()->getParent();
+ return PSV->isConstant(MF.getFrameInfo());
+ } else {
+ return AA->pointsToConstantMemory(MMO->getValue());
+ }
+}
+
/// IsProfitableToHoist - Return true if it is potentially profitable to hoist
/// the given loop invariant.
bool MachineLICM::IsProfitableToHoist(MachineInstr &MI) {
// FIXME: For now, only hoist re-materilizable instructions. LICM will
// increase register pressure. We want to make sure it doesn't increase
// spilling.
- if (!TII->isTriviallyReMaterializable(&MI, AA))
- return false;
+ // Also hoist loads from constant memory, e.g. load from stubs, GOT. Hoisting
+ // these tend to help performance in low register pressure situation. The
+ // trade off is it may cause spill in high pressure situation. It will end up
+ // adding a store in the loop preheader. But the reload is no more expensive.
+ // The side benefit is these loads are frequently CSE'ed.
+ if (!TII->isTriviallyReMaterializable(&MI, AA)) {
+ if (!isLoadFromConstantMemory(&MI))
+ return false;
+ }
// If result(s) of this instruction is used by PHIs, then don't hoist it.
// The presence of joins makes it difficult for current register allocator
// If not, we may be able to unfold a load and hoist that.
// First test whether the instruction is loading from an amenable
// memory location.
- if (!MI->getDesc().mayLoad()) return 0;
- if (!MI->hasOneMemOperand()) return 0;
- MachineMemOperand *MMO = *MI->memoperands_begin();
- if (MMO->isVolatile()) return 0;
- MachineFunction &MF = *MI->getParent()->getParent();
- if (!MMO->getValue()) return 0;
- if (const PseudoSourceValue *PSV =
- dyn_cast<PseudoSourceValue>(MMO->getValue())) {
- if (!PSV->isConstant(MF.getFrameInfo())) return 0;
- } else {
- if (!AA->pointsToConstantMemory(MMO->getValue())) return 0;
- }
+ if (!isLoadFromConstantMemory(MI))
+ return 0;
+
// Next determine the register class for a temporary register.
unsigned LoadRegIndex;
unsigned NewOpc =
const TargetRegisterClass *RC = TID.OpInfo[LoadRegIndex].getRegClass(TRI);
// Ok, we're unfolding. Create a temporary register and do the unfold.
unsigned Reg = RegInfo->createVirtualRegister(RC);
+
+ MachineFunction &MF = *MI->getParent()->getParent();
SmallVector<MachineInstr *, 2> NewMIs;
bool Success =
TII->unfoldMemoryOperand(MF, MI, Reg,
}
}
-static const MachineInstr *LookForDuplicate(const MachineInstr *MI,
- std::vector<const MachineInstr*> &PrevMIs,
- MachineRegisterInfo *RegInfo) {
- unsigned NumOps = MI->getNumOperands();
+const MachineInstr*
+MachineLICM::LookForDuplicate(const MachineInstr *MI,
+ std::vector<const MachineInstr*> &PrevMIs) {
for (unsigned i = 0, e = PrevMIs.size(); i != e; ++i) {
const MachineInstr *PrevMI = PrevMIs[i];
- unsigned NumOps2 = PrevMI->getNumOperands();
- if (NumOps != NumOps2)
- continue;
- bool IsSame = true;
- for (unsigned j = 0; j != NumOps; ++j) {
- const MachineOperand &MO = MI->getOperand(j);
- if (MO.isReg() && MO.isDef()) {
- if (RegInfo->getRegClass(MO.getReg()) !=
- RegInfo->getRegClass(PrevMI->getOperand(j).getReg())) {
- IsSame = false;
- break;
- }
- continue;
- }
- if (!MO.isIdenticalTo(PrevMI->getOperand(j))) {
- IsSame = false;
- break;
- }
- }
- if (IsSame)
+ if (TII->isIdentical(MI, PrevMI, RegInfo))
return PrevMI;
}
return 0;
bool MachineLICM::EliminateCSE(MachineInstr *MI,
DenseMap<unsigned, std::vector<const MachineInstr*> >::iterator &CI) {
- if (CI != CSEMap.end()) {
- if (const MachineInstr *Dup = LookForDuplicate(MI, CI->second, RegInfo)) {
- DEBUG(errs() << "CSEing " << *MI << " with " << *Dup);
- for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
- const MachineOperand &MO = MI->getOperand(i);
- if (MO.isReg() && MO.isDef())
- RegInfo->replaceRegWith(MO.getReg(), Dup->getOperand(i).getReg());
- }
- MI->eraseFromParent();
- ++NumCSEed;
- return true;
+ if (CI == CSEMap.end())
+ return false;
+
+ if (const MachineInstr *Dup = LookForDuplicate(MI, CI->second)) {
+ DEBUG(errs() << "CSEing " << *MI << " with " << *Dup);
+ for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
+ const MachineOperand &MO = MI->getOperand(i);
+ if (MO.isReg() && MO.isDef())
+ RegInfo->replaceRegWith(MO.getReg(), Dup->getOperand(i).getReg());
}
+ MI->eraseFromParent();
+ ++NumCSEed;
+ return true;
}
return false;
}
errs() << "Hoisting " << *MI;
if (CurPreheader->getBasicBlock())
errs() << " to MachineBasicBlock "
- << CurPreheader->getBasicBlock()->getName();
+ << CurPreheader->getName();
if (MI->getParent()->getBasicBlock())
errs() << " from MachineBasicBlock "
- << MI->getParent()->getBasicBlock()->getName();
+ << MI->getParent()->getName();
errs() << "\n";
});
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