[llvm-commits] [llvm] r84761 - /llvm/trunk/lib/CodeGen/PrologEpilogInserter.cpp
Jim Grosbach
grosbach at apple.com
Wed Oct 21 08:26:25 PDT 2009
Author: grosbach
Date: Wed Oct 21 10:26:21 2009
New Revision: 84761
URL: http://llvm.org/viewvc/llvm-project?rev=84761&view=rev
Log:
Cleanup of frame index scavenging. Better code flow and more accurately
handles T2 and ARM use cases.
Modified:
llvm/trunk/lib/CodeGen/PrologEpilogInserter.cpp
Modified: llvm/trunk/lib/CodeGen/PrologEpilogInserter.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/PrologEpilogInserter.cpp?rev=84761&r1=84760&r2=84761&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/PrologEpilogInserter.cpp (original)
+++ llvm/trunk/lib/CodeGen/PrologEpilogInserter.cpp Wed Oct 21 10:26:21 2009
@@ -729,10 +729,12 @@
/// 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 @@
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 @@
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 @@
// 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 @@
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 @@
// 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 @@
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;
+ }
}
}
}
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