+/// RewriteInstruction - Rewrite specified instruction by replacing references
+/// to old frame index with new one.
+void StackSlotColoring::RewriteInstruction(MachineInstr *MI, int OldFI,
+ int NewFI, MachineFunction &MF) {
+ // Update the operands.
+ for (unsigned i = 0, ee = MI->getNumOperands(); i != ee; ++i) {
+ MachineOperand &MO = MI->getOperand(i);
+ if (!MO.isFI())
+ continue;
+ int FI = MO.getIndex();
+ if (FI != OldFI)
+ continue;
+ MO.setIndex(NewFI);
+ }
+
+ // Update the memory references. This changes the MachineMemOperands
+ // directly. They may be in use by multiple instructions, however all
+ // instructions using OldFI are being rewritten to use NewFI.
+ const Value *OldSV = PseudoSourceValue::getFixedStack(OldFI);
+ const Value *NewSV = PseudoSourceValue::getFixedStack(NewFI);
+ for (MachineInstr::mmo_iterator I = MI->memoperands_begin(),
+ E = MI->memoperands_end(); I != E; ++I)
+ if ((*I)->getValue() == OldSV)
+ (*I)->setValue(NewSV);
+}
+
+
+/// RemoveDeadStores - Scan through a basic block and look for loads followed
+/// by stores. If they're both using the same stack slot, then the store is
+/// definitely dead. This could obviously be much more aggressive (consider
+/// pairs with instructions between them), but such extensions might have a
+/// considerable compile time impact.
+bool StackSlotColoring::RemoveDeadStores(MachineBasicBlock* MBB) {
+ // FIXME: This could be much more aggressive, but we need to investigate
+ // the compile time impact of doing so.
+ bool changed = false;
+
+ SmallVector<MachineInstr*, 4> toErase;
+
+ for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end();
+ I != E; ++I) {
+ if (DCELimit != -1 && (int)NumDead >= DCELimit)
+ break;
+
+ MachineBasicBlock::iterator NextMI = llvm::next(I);
+ if (NextMI == MBB->end()) continue;
+
+ int FirstSS, SecondSS;
+ unsigned LoadReg = 0;
+ unsigned StoreReg = 0;
+ if (!(LoadReg = TII->isLoadFromStackSlot(I, FirstSS))) continue;
+ if (!(StoreReg = TII->isStoreToStackSlot(NextMI, SecondSS))) continue;
+ if (FirstSS != SecondSS || LoadReg != StoreReg || FirstSS == -1) continue;
+
+ ++NumDead;
+ changed = true;
+
+ if (NextMI->findRegisterUseOperandIdx(LoadReg, true, 0) != -1) {
+ ++NumDead;
+ toErase.push_back(I);
+ }
+
+ toErase.push_back(NextMI);
+ ++I;
+ }
+
+ for (SmallVector<MachineInstr*, 4>::iterator I = toErase.begin(),
+ E = toErase.end(); I != E; ++I)
+ (*I)->eraseFromParent();
+
+ return changed;
+}
+
+