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Remove the now obsolete frame index virtual re-use algorithm from PEI. Pre-RA 

virtual base registers handle this function, and more. A bit more cleanup
to do on the interface to eliminateFrameIndex() after this.

llvm-svn: 112237
This commit is contained in:
Jim Grosbach 2010-08-26 22:42:12 +00:00
parent c19e3a0946
commit 2a1915d04b
1 changed files with 9 additions and 148 deletions
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157
llvm/lib/CodeGen/PrologEpilogInserter.cpp
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@ -793,38 +793,6 @@ void PEI::replaceFrameIndices(MachineFunction &Fn) {
}
}
/// findLastUseReg - find the killing use of the specified register within
/// the instruciton range. Return the operand number of the kill in Operand.
static MachineBasicBlock::iterator
findLastUseReg(MachineBasicBlock::iterator I, MachineBasicBlock::iterator ME,
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();
if (OpReg == 0 || !TargetRegisterInfo::isVirtualRegister(OpReg))
continue;
assert (OpReg == Reg
&& "overlapping use of scavenged index register!");
// 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.
assert (0 && "scavenged index register never killed!");
return ME;
}
/// scavengeFrameVirtualRegs - Replace all frame index virtual registers
/// with physical registers. Use the register scavenger to find an
/// appropriate register to use.
@ -834,27 +802,14 @@ 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;
TargetRegisterInfo::FrameIndexValue PrevValue(0,0);
TargetRegisterInfo::FrameIndexValue Value(0,0);
MachineInstr *PrevLastUseMI = NULL;
unsigned PrevLastUseOp = 0;
bool trackingCurrentValue = false;
unsigned VirtReg = 0;
unsigned ScratchReg = 0;
int SPAdj = 0;
// The instruction stream may change in the loop, so check BB->end()
// directly.
for (MachineBasicBlock::iterator I = BB->begin(); I != BB->end(); ) {
MachineInstr *MI = I;
bool isDefInsn = false;
bool isKillInsn = false;
bool clobbersScratchReg = false;
bool DoIncr = true;
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
if (MI->getOperand(i).isReg()) {
@ -862,124 +817,30 @@ void PEI::scavengeFrameVirtualRegs(MachineFunction &Fn) {
unsigned Reg = MO.getReg();
if (Reg == 0)
continue;
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 == CurrentScratchReg) {
if (MO.isUse()) {
// Two-address operands implicitly kill
if (MO.isKill() || MI->isRegTiedToDefOperand(i))
clobbersScratchReg = true;
} else {
assert (MO.isDef());
clobbersScratchReg = true;
}
}
if (!TargetRegisterInfo::isVirtualRegister(Reg))
continue;
}
++NumVirtualFrameRegs;
// If this is a def, remember that this insn defines the value.
// This lets us properly consider insns which re-use the scratch
// register, such as r2 = sub r2, #imm, in the middle of the
// scratch range.
if (MO.isDef())
isDefInsn = true;
// Have we already allocated a scratch register for this virtual?
if (Reg != CurrentVirtReg) {
if (Reg != VirtReg) {
// When we first encounter a new virtual register, it
// must be a definition.
assert(MI->getOperand(i).isDef() &&
"frame index virtual missing def!");
// We can't have nested virtual register live ranges because
// there's only a guarantee of one scavenged register at a time.
assert (CurrentVirtReg == 0 &&
"overlapping frame index virtual registers!");
// If the target gave us information about what's in the register,
// we can use that to re-use scratch regs.
DenseMap<unsigned, FrameConstantEntry>::iterator Entry =
FrameConstantRegMap.find(Reg);
trackingCurrentValue = Entry != FrameConstantRegMap.end();
if (trackingCurrentValue) {
SPAdj = (*Entry).second.second;
Value = (*Entry).second.first;
} else {
SPAdj = 0;
Value.first = 0;
Value.second = 0;
}
// If the scratch register from the last allocation is still
// available, see if the value matches. If it does, just re-use it.
if (trackingCurrentValue && havePrevValue && PrevValue == Value) {
// FIXME: This assumes that the instructions in the live range
// 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. 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);
// Remove all instructions up 'til the last use, since they're
// just calculating the value we already have.
BB->erase(I, LastUseMI);
I = LastUseMI;
// Extend the live range of the scratch register
PrevLastUseMI->getOperand(PrevLastUseOp).setIsKill(false);
RS->setUsed(CurrentScratchReg);
CurrentVirtReg = Reg;
// 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;
VirtReg = Reg;
const TargetRegisterClass *RC = Fn.getRegInfo().getRegClass(Reg);
CurrentScratchReg = RS->scavengeRegister(RC, I, SPAdj);
PrevValue = Value;
ScratchReg = RS->scavengeRegister(RC, I, SPAdj);
++NumScavengedRegs;
}
// replace this reference to the virtual register with the
// scratch register.
assert (CurrentScratchReg && "Missing scratch register!");
MI->getOperand(i).setReg(CurrentScratchReg);
assert (ScratchReg && "Missing scratch register!");
MI->getOperand(i).setReg(ScratchReg);
if (MI->getOperand(i).isKill()) {
isKillInsn = true;
PrevLastUseOp = i;
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) {
CurrentVirtReg = 0;
havePrevValue = trackingCurrentValue;
}
// 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;