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MachineCSE: Add a target query for the LookAheadLimit heurisitic

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This is used to determine whether or not to CSE physical register
defs.

Differential Revision: http://reviews.llvm.org/D9472

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@236923 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Tom Stellard 2015-05-09 00:56:07 +00:00
parent f5b930b2e2
commit 7d66bd3e7f
3 changed files with 13 additions and 2 deletions
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8
include/llvm/Target/TargetInstrInfo.h
View File

@ -1235,6 +1235,14 @@ public:
return false;
}
/// \brief Return the value to use for the MachineCSE's LookAheadLimit,
/// which is a heuristic used for CSE'ing phys reg defs.
virtual unsigned getMachineCSELookAheadLimit () const {
// The default lookahead is small to prevent unprofitable quadratic
// behavior.
return 5;
}
private:
int CallFrameSetupOpcode, CallFrameDestroyOpcode;
};

5
lib/CodeGen/MachineCSE.cpp
View File

@ -48,7 +48,7 @@ namespace {
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());
}
@ -69,7 +69,7 @@ namespace {
}
private:
const unsigned LookAheadLimit;
unsigned LookAheadLimit;
typedef RecyclingAllocator<BumpPtrAllocator,
ScopedHashTableVal<MachineInstr*, unsigned> > AllocatorTy;
typedef ScopedHashTable<MachineInstr*, unsigned,
@ -716,5 +716,6 @@ bool MachineCSE::runOnMachineFunction(MachineFunction &MF) {
MRI = &MF.getRegInfo();
AA = &getAnalysis<AliasAnalysis>();
DT = &getAnalysis<MachineDominatorTree>();
LookAheadLimit = TII->getMachineCSELookAheadLimit();
return PerformCSE(DT->getRootNode());
}

2
lib/Target/R600/SIInstrInfo.h
View File

@ -142,6 +142,8 @@ public:
bool FoldImmediate(MachineInstr *UseMI, MachineInstr *DefMI,
unsigned Reg, MachineRegisterInfo *MRI) const final;
unsigned getMachineCSELookAheadLimit() const override { return 500; }
bool isSALU(uint16_t Opcode) const {
return get(Opcode).TSFlags & SIInstrFlags::SALU;
}