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When spilling a live range that is used multiple times by one instruction,

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only add a reload live range once for the instruction.  This is one step
towards fixing a regalloc pessimization that Nate notice, but is later undone
by the spiller (so no code is changed).

llvm-svn: 23293
This commit is contained in:
Chris Lattner 2005-09-09 19:17:47 +00:00
parent 8d654c32cb
commit 8d8506f8e2
1 changed files with 26 additions and 9 deletions
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35
lib/CodeGen/LiveIntervalAnalysis.cpp
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@ -249,14 +249,26 @@ addIntervalsForSpills(const LiveInterval &li, VirtRegMap &vrm, int slot) {
MachineBasicBlock::iterator mi = getInstructionFromIndex(index);
// NewRegLiveIn - This instruction might have multiple uses of the spilled
// register. In this case, for the first use, keep track of the new vreg
// that we reload it into. If we see a second use, reuse this vreg
// instead of creating live ranges for two reloads.
unsigned NewRegLiveIn = 0;
for_operand:
for (unsigned i = 0; i != mi->getNumOperands(); ++i) {
MachineOperand& mop = mi->getOperand(i);
if (mop.isRegister() && mop.getReg() == li.reg) {
// First thing, attempt to fold the memory reference into the
// instruction. If we can do this, we don't need to insert spill
// code.
if (MachineInstr* fmi = mri_->foldMemoryOperand(mi, i, slot)) {
if (NewRegLiveIn && mop.isUse()) {
// We already emitted a reload of this value, reuse it for
// subsequent operands.
mi->SetMachineOperandReg(i, NewRegLiveIn);
DEBUG(std::cerr << "\t\t\t\treused reload into reg" << NewRegLiveIn
<< " for operand #" << i << '\n');
mi->dump();
} else if (MachineInstr* fmi = mri_->foldMemoryOperand(mi, i, slot)) {
// Attempt to fold the memory reference into the instruction. If we
// can do this, we don't need to insert spill code.
if (lv_)
lv_->instructionChanged(mi, fmi);
vrm.virtFolded(li.reg, mi, i, fmi);
@ -288,11 +300,11 @@ addIntervalsForSpills(const LiveInterval &li, VirtRegMap &vrm, int slot) {
getUseIndex(index));
// create a new register for this spill
unsigned nReg = mf_->getSSARegMap()->createVirtualRegister(rc);
mi->SetMachineOperandReg(i, nReg);
NewRegLiveIn = mf_->getSSARegMap()->createVirtualRegister(rc);
mi->SetMachineOperandReg(i, NewRegLiveIn);
vrm.grow();
vrm.assignVirt2StackSlot(nReg, slot);
LiveInterval& nI = getOrCreateInterval(nReg);
vrm.assignVirt2StackSlot(NewRegLiveIn, slot);
LiveInterval& nI = getOrCreateInterval(NewRegLiveIn);
assert(nI.empty());
// the spill weight is now infinity as it
@ -305,7 +317,12 @@ addIntervalsForSpills(const LiveInterval &li, VirtRegMap &vrm, int slot) {
// update live variables if it is available
if (lv_)
lv_->addVirtualRegisterKilled(nReg, mi);
lv_->addVirtualRegisterKilled(NewRegLiveIn, mi);
// If this is a live in, reuse it for subsequent live-ins. If it's
// a def, we can't do this.
if (!mop.isUse()) NewRegLiveIn = 0;
DEBUG(std::cerr << "\t\t\t\tadded new interval: " << nI << '\n');
}
}