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Cleanup of frame index scavenging. Better code flow and more accurately

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handles T2 and ARM use cases.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@84761 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Jim Grosbach 2009-10-21 15:26:21 +00:00
parent 2ba7a90126
commit 3325537682
1 changed files with 60 additions and 35 deletions
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95
lib/CodeGen/PrologEpilogInserter.cpp
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@ -729,10 +729,12 @@ void PEI::replaceFrameIndices(MachineFunction &Fn) {
/// the instruciton range. Return the operand number of the kill in Operand.
static MachineBasicBlock::iterator
findLastUseReg(MachineBasicBlock::iterator I, MachineBasicBlock::iterator ME,
unsigned Reg, unsigned *Operand) {
unsigned Reg) {
// Scan forward to find the last use of this virtual register
for (++I; I != ME; ++I) {
MachineInstr *MI = I;
bool isDefInsn = false;
bool isKillInsn = false;
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i)
if (MI->getOperand(i).isReg()) {
unsigned OpReg = MI->getOperand(i).getReg();
@ -740,13 +742,14 @@ findLastUseReg(MachineBasicBlock::iterator I, MachineBasicBlock::iterator ME,
continue;
assert (OpReg == Reg
&& "overlapping use of scavenged index register!");
// If this is the killing use, we're done
if (MI->getOperand(i).isKill()) {
if (Operand)
*Operand = i;
return I;
}
// If this is the killing use, we have a candidate.
if (MI->getOperand(i).isKill())
isKillInsn = true;
else if (MI->getOperand(i).isDef())
isDefInsn = true;
}
if (isKillInsn && !isDefInsn)
return I;
}
// If we hit the end of the basic block, there was no kill of
// the virtual register, which is wrong.
@ -763,10 +766,13 @@ void PEI::scavengeFrameVirtualRegs(MachineFunction &Fn) {
E = Fn.end(); BB != E; ++BB) {
RS->enterBasicBlock(BB);
// FIXME: The logic flow in this function is still too convoluted.
// It needs a cleanup refactoring. Do that in preparation for tracking
// more than one scratch register value and using ranges to find
// available scratch registers.
unsigned CurrentVirtReg = 0;
unsigned CurrentScratchReg = 0;
bool havePrevValue = false;
unsigned PrevScratchReg = 0;
int PrevValue = 0;
MachineInstr *PrevLastUseMI = NULL;
unsigned PrevLastUseOp = 0;
@ -776,11 +782,13 @@ void PEI::scavengeFrameVirtualRegs(MachineFunction &Fn) {
// The instruction stream may change in the loop, so check BB->end()
// directly.
for (MachineBasicBlock::iterator I = BB->begin(); I != BB->end(); ++I) {
for (MachineBasicBlock::iterator I = BB->begin(); I != BB->end(); ) {
MachineInstr *MI = I;
bool isDefInsn = false;
bool isKillInsn = false;
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i)
bool clobbersScratchReg = false;
bool DoIncr = true;
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
if (MI->getOperand(i).isReg()) {
MachineOperand &MO = MI->getOperand(i);
unsigned Reg = MO.getReg();
@ -789,17 +797,14 @@ void PEI::scavengeFrameVirtualRegs(MachineFunction &Fn) {
if (!TargetRegisterInfo::isVirtualRegister(Reg)) {
// If we have a previous scratch reg, check and see if anything
// here kills whatever value is in there.
if (Reg == PrevScratchReg) {
if (Reg == CurrentScratchReg) {
if (MO.isUse()) {
// Two-address operands implicitly kill
if (MO.isKill() || MI->isRegTiedToDefOperand(i)) {
havePrevValue = false;
PrevScratchReg = 0;
}
if (MO.isKill() || MI->isRegTiedToDefOperand(i))
clobbersScratchReg = true;
} else {
assert (MO.isDef());
havePrevValue = false;
PrevScratchReg = 0;
clobbersScratchReg = true;
}
}
continue;
@ -840,37 +845,46 @@ void PEI::scavengeFrameVirtualRegs(MachineFunction &Fn) {
// for the virtual register are exclusively for the purpose
// of populating the value in the register. That's reasonable
// for these frame index registers, but it's still a very, very
// strong assumption. Perhaps this implies that the frame index
// elimination should be before register allocation, with
// conservative heuristics since we'll know less then, and
// the reuse calculations done directly when doing the code-gen?
// strong assumption. rdar://7322732. Better would be to
// explicitly check each instruction in the range for references
// to the virtual register. Only delete those insns that
// touch the virtual register.
// Find the last use of the new virtual register. Remove all
// instruction between here and there, and update the current
// instruction to reference the last use insn instead.
MachineBasicBlock::iterator LastUseMI =
findLastUseReg(I, BB->end(), Reg, &i);
findLastUseReg(I, BB->end(), Reg);
// Remove all instructions up 'til the last use, since they're
// just calculating the value we already have.
BB->erase(I, LastUseMI);
MI = I = LastUseMI;
e = MI->getNumOperands();
CurrentScratchReg = PrevScratchReg;
// Extend the live range of the register
// Extend the live range of the scratch register
PrevLastUseMI->getOperand(PrevLastUseOp).setIsKill(false);
RS->setUsed(CurrentScratchReg);
} else {
CurrentVirtReg = Reg;
const TargetRegisterClass *RC = Fn.getRegInfo().getRegClass(Reg);
CurrentScratchReg = RS->FindUnusedReg(RC);
if (CurrentScratchReg == 0)
// No register is "free". Scavenge a register.
CurrentScratchReg = RS->scavengeRegister(RC, I, SPAdj);
PrevValue = Value;
// We deleted the instruction we were scanning the operands of.
// Jump back to the instruction iterator loop. Don't increment
// past this instruction since we updated the iterator already.
DoIncr = false;
break;
}
// Scavenge a new scratch register
CurrentVirtReg = Reg;
const TargetRegisterClass *RC = Fn.getRegInfo().getRegClass(Reg);
CurrentScratchReg = RS->FindUnusedReg(RC);
if (CurrentScratchReg == 0)
// No register is "free". Scavenge a register.
CurrentScratchReg = RS->scavengeRegister(RC, I, SPAdj);
PrevValue = Value;
}
// replace this reference to the virtual register with the
// scratch register.
assert (CurrentScratchReg && "Missing scratch register!");
MI->getOperand(i).setReg(CurrentScratchReg);
@ -880,15 +894,26 @@ void PEI::scavengeFrameVirtualRegs(MachineFunction &Fn) {
PrevLastUseMI = MI;
}
}
}
// If this is the last use of the scratch, stop tracking it. The
// last use will be a kill operand in an instruction that does
// not also define the scratch register.
if (isKillInsn && !isDefInsn) {
PrevScratchReg = CurrentScratchReg;
CurrentScratchReg = CurrentVirtReg = 0;
CurrentVirtReg = 0;
havePrevValue = trackingCurrentValue;
}
RS->forward(MI);
// Similarly, notice if instruction clobbered the value in the
// register we're tracking for possible later reuse. This is noted
// above, but enforced here since the value is still live while we
// process the rest of the operands of the instruction.
if (clobbersScratchReg) {
havePrevValue = false;
CurrentScratchReg = 0;
}
if (DoIncr) {
RS->forward(I);
++I;
}
}
}
}