+
+static inline bool
+lookupCandidateBaseReg(int64_t BaseOffset,
+ int64_t FrameSizeAdjust,
+ int64_t LocalFrameOffset,
+ const MachineInstr *MI,
+ const TargetRegisterInfo *TRI) {
+ // Check if the relative offset from the where the base register references
+ // to the target address is in range for the instruction.
+ int64_t Offset = FrameSizeAdjust + LocalFrameOffset - BaseOffset;
+ return TRI->isFrameOffsetLegal(MI, Offset);
+}
+
+bool LocalStackSlotPass::insertFrameReferenceRegisters(MachineFunction &Fn) {
+ // Scan the function's instructions looking for frame index references.
+ // For each, ask the target if it wants a virtual base register for it
+ // based on what we can tell it about where the local will end up in the
+ // stack frame. If it wants one, re-use a suitable one we've previously
+ // allocated, or if there isn't one that fits the bill, allocate a new one
+ // and ask the target to create a defining instruction for it.
+ bool UsedBaseReg = false;
+
+ MachineFrameInfo *MFI = Fn.getFrameInfo();
+ const TargetRegisterInfo *TRI = Fn.getTarget().getRegisterInfo();
+ const TargetFrameLowering &TFI = *Fn.getTarget().getFrameLowering();
+ bool StackGrowsDown =
+ TFI.getStackGrowthDirection() == TargetFrameLowering::StackGrowsDown;
+
+ // Collect all of the instructions in the block that reference
+ // a frame index. Also store the frame index referenced to ease later
+ // lookup. (For any insn that has more than one FI reference, we arbitrarily
+ // choose the first one).
+ SmallVector<FrameRef, 64> FrameReferenceInsns;
+
+ for (MachineFunction::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB) {
+ for (MachineBasicBlock::iterator I = BB->begin(); I != BB->end(); ++I) {
+ MachineInstr *MI = I;
+
+ // Debug value, stackmap and patchpoint instructions can't be out of
+ // range, so they don't need any updates.
+ if (MI->isDebugValue() ||
+ MI->getOpcode() == TargetOpcode::STACKMAP ||
+ MI->getOpcode() == TargetOpcode::PATCHPOINT)
+ continue;
+
+ // For now, allocate the base register(s) within the basic block
+ // where they're used, and don't try to keep them around outside
+ // of that. It may be beneficial to try sharing them more broadly
+ // than that, but the increased register pressure makes that a
+ // tricky thing to balance. Investigate if re-materializing these
+ // becomes an issue.
+ for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
+ // Consider replacing all frame index operands that reference
+ // an object allocated in the local block.
+ if (MI->getOperand(i).isFI()) {
+ // Don't try this with values not in the local block.
+ if (!MFI->isObjectPreAllocated(MI->getOperand(i).getIndex()))
+ break;
+ int Idx = MI->getOperand(i).getIndex();
+ int64_t LocalOffset = LocalOffsets[Idx];
+ if (!TRI->needsFrameBaseReg(MI, LocalOffset))
+ break;
+ FrameReferenceInsns.
+ push_back(FrameRef(MI, LocalOffset, Idx));
+ break;
+ }
+ }
+ }
+ }
+
+ // Sort the frame references by local offset
+ array_pod_sort(FrameReferenceInsns.begin(), FrameReferenceInsns.end());
+
+ MachineBasicBlock *Entry = Fn.begin();
+
+ unsigned BaseReg = 0;
+ int64_t BaseOffset = 0;
+
+ // Loop through the frame references and allocate for them as necessary.
+ for (int ref = 0, e = FrameReferenceInsns.size(); ref < e ; ++ref) {
+ FrameRef &FR = FrameReferenceInsns[ref];
+ MachineBasicBlock::iterator I = FR.getMachineInstr();
+ MachineInstr *MI = I;
+ int64_t LocalOffset = FR.getLocalOffset();
+ int FrameIdx = FR.getFrameIndex();
+ assert(MFI->isObjectPreAllocated(FrameIdx) &&
+ "Only pre-allocated locals expected!");
+
+ DEBUG(dbgs() << "Considering: " << *MI);
+
+ unsigned idx = 0;
+ for (unsigned f = MI->getNumOperands(); idx != f; ++idx) {
+ if (!MI->getOperand(idx).isFI())
+ continue;
+
+ if (FrameIdx == I->getOperand(idx).getIndex())
+ break;
+ }
+
+ assert(idx < MI->getNumOperands() && "Cannot find FI operand");
+
+ int64_t Offset = 0;
+ int64_t FrameSizeAdjust = StackGrowsDown ? MFI->getLocalFrameSize() : 0;
+
+ DEBUG(dbgs() << " Replacing FI in: " << *MI);
+
+ // If we have a suitable base register available, use it; otherwise
+ // create a new one. Note that any offset encoded in the
+ // instruction itself will be taken into account by the target,
+ // so we don't have to adjust for it here when reusing a base
+ // register.
+ if (UsedBaseReg && lookupCandidateBaseReg(BaseOffset, FrameSizeAdjust,
+ LocalOffset, MI, TRI)) {
+ DEBUG(dbgs() << " Reusing base register " << BaseReg << "\n");
+ // We found a register to reuse.
+ Offset = FrameSizeAdjust + LocalOffset - BaseOffset;
+ } else {
+ // No previously defined register was in range, so create a // new one.
+
+ int64_t InstrOffset = TRI->getFrameIndexInstrOffset(MI, idx);
+
+ int64_t PrevBaseOffset = BaseOffset;
+ BaseOffset = FrameSizeAdjust + LocalOffset + InstrOffset;
+
+ // We'd like to avoid creating single-use virtual base registers.
+ // Because the FrameRefs are in sorted order, and we've already
+ // processed all FrameRefs before this one, just check whether or not
+ // the next FrameRef will be able to reuse this new register. If not,
+ // then don't bother creating it.
+ bool CanReuse = false;
+ for (int refn = ref + 1; refn < e; ++refn) {
+ FrameRef &FRN = FrameReferenceInsns[refn];
+ MachineBasicBlock::iterator J = FRN.getMachineInstr();
+ MachineInstr *MIN = J;
+
+ CanReuse = lookupCandidateBaseReg(BaseOffset, FrameSizeAdjust,
+ FRN.getLocalOffset(), MIN, TRI);
+ break;
+ }
+
+ if (!CanReuse) {
+ BaseOffset = PrevBaseOffset;
+ continue;
+ }
+
+ const MachineFunction *MF = MI->getParent()->getParent();
+ const TargetRegisterClass *RC = TRI->getPointerRegClass(*MF);
+ BaseReg = Fn.getRegInfo().createVirtualRegister(RC);
+
+ DEBUG(dbgs() << " Materializing base register " << BaseReg <<
+ " at frame local offset " << LocalOffset + InstrOffset << "\n");
+
+ // Tell the target to insert the instruction to initialize
+ // the base register.
+ // MachineBasicBlock::iterator InsertionPt = Entry->begin();
+ TRI->materializeFrameBaseRegister(Entry, BaseReg, FrameIdx,
+ InstrOffset);
+
+ // The base register already includes any offset specified
+ // by the instruction, so account for that so it doesn't get
+ // applied twice.
+ Offset = -InstrOffset;
+
+ ++NumBaseRegisters;
+ UsedBaseReg = true;
+ }
+ assert(BaseReg != 0 && "Unable to allocate virtual base register!");
+
+ // Modify the instruction to use the new base register rather
+ // than the frame index operand.
+ TRI->resolveFrameIndex(I, BaseReg, Offset);
+ DEBUG(dbgs() << "Resolved: " << *MI);
+
+ ++NumReplacements;
+ }
+
+ return UsedBaseReg;
+}