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Add a simple little improvement to the local spiller to keep track of stores 

and delete them if they turn out to be dead.  This is a useful little hack
that even speeds up some programs.  For example, it speeds up Ptrdist/ks
from 17.53s to 15.59s, and 188.ammp from 149s to 146s.

This also speeds up llc :)

llvm-svn: 16630
This commit is contained in:
Chris Lattner 2004-10-01 19:47:12 +00:00
parent d3b1f6c703
commit 04f52079d7
1 changed files with 26 additions and 0 deletions
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26
llvm/lib/CodeGen/VirtRegMap.cpp
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@ -35,6 +35,7 @@ namespace {
Statistic<> NumStores("spiller", "Number of stores added");
Statistic<> NumLoads ("spiller", "Number of loads added");
Statistic<> NumReused("spiller", "Number of values reused");
Statistic<> NumDSE ("spiller", "Number of dead stores elided");
enum SpillerName { simple, local };
@ -283,6 +284,14 @@ void LocalSpiller::RewriteMBB(MachineBasicBlock &MBB, const VirtRegMap &VRM) {
// and ".second" is the virtual register that is spilled.
std::vector<std::pair<unsigned, unsigned> > DefAndUseVReg;
// MaybeDeadStores - When we need to write a value back into a stack slot,
// keep track of the inserted store. If the stack slot value is never read
// (because the value was used from some available register, for example), and
// subsequently stored to, the original store is dead. This map keeps track
// of inserted stores that are not used. If we see a subsequent store to the
// same stack slot, the original store is deleted.
std::map<int, MachineInstr*> MaybeDeadStores;
for (MachineBasicBlock::iterator MII = MBB.begin(), E = MBB.end();
MII != E; ) {
MachineInstr &MI = *MII;
@ -361,6 +370,9 @@ void LocalSpiller::RewriteMBB(MachineBasicBlock &MBB, const VirtRegMap &VRM) {
ClobberPhysReg(Op.AssignedPhysReg, SpillSlotsAvailable,
PhysRegsAvailable);
// Any stores to this stack slot are not dead anymore.
MaybeDeadStores.erase(Op.StackSlot);
MI.SetMachineOperandReg(Op.Operand, Op.AssignedPhysReg);
PhysRegsAvailable[Op.AssignedPhysReg] = Op.StackSlot;
SpillSlotsAvailable[Op.StackSlot] = Op.AssignedPhysReg;
@ -383,6 +395,9 @@ void LocalSpiller::RewriteMBB(MachineBasicBlock &MBB, const VirtRegMap &VRM) {
// This invalidates PhysReg.
ClobberPhysReg(PhysReg, SpillSlotsAvailable, PhysRegsAvailable);
// Any stores to this stack slot are not dead anymore.
MaybeDeadStores.erase(StackSlot);
MI.SetMachineOperandReg(i, PhysReg);
PhysRegsAvailable[PhysReg] = StackSlot;
SpillSlotsAvailable[StackSlot] = PhysReg;
@ -423,6 +438,9 @@ void LocalSpiller::RewriteMBB(MachineBasicBlock &MBB, const VirtRegMap &VRM) {
int SS = VRM.getStackSlot(I->second);
DEBUG(std::cerr << " - StackSlot: " << SS << "\n");
// Any stores to this stack slot are not dead anymore.
MaybeDeadStores.erase(SS);
std::map<int, unsigned>::iterator I = SpillSlotsAvailable.find(SS);
if (I != SpillSlotsAvailable.end()) {
PhysRegsAvailable.erase(I->second);
@ -476,6 +494,14 @@ void LocalSpiller::RewriteMBB(MachineBasicBlock &MBB, const VirtRegMap &VRM) {
DEBUG(std::cerr << "Store:\t" << *next(MII));
MI.SetMachineOperandReg(i, PhysReg);
// If there is a dead store to this stack slot, nuke it now.
MachineInstr *&LastStore = MaybeDeadStores[StackSlot];
if (LastStore) {
++NumDSE;
MBB.erase(LastStore);
}
LastStore = next(MII);
// If the stack slot value was previously available in some other
// register, change it now. Otherwise, make the register available,
// in PhysReg.