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+//===- LocalStackSlotAllocation.cpp - Pre-allocate locals to stack slots --===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This pass assigns local frame indices to stack slots relative to one another
+// and allocates additional base registers to access them when the target
+// estimates they are likely to be out of range of stack pointer and frame
+// pointer relative addressing.
+//
+//===----------------------------------------------------------------------===//
+
+#define DEBUG_TYPE "localstackalloc"
+#include "llvm/Constants.h"
+#include "llvm/DerivedTypes.h"
+#include "llvm/Instructions.h"
+#include "llvm/Intrinsics.h"
+#include "llvm/LLVMContext.h"
+#include "llvm/Module.h"
+#include "llvm/Pass.h"
+#include "llvm/ADT/SmallSet.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/CodeGen/MachineFrameInfo.h"
+#include "llvm/CodeGen/MachineFunction.h"
+#include "llvm/CodeGen/MachineFunctionPass.h"
+#include "llvm/CodeGen/MachineRegisterInfo.h"
+#include "llvm/CodeGen/Passes.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/ErrorHandling.h"
+#include "llvm/Support/raw_ostream.h"
+#include "llvm/Target/TargetRegisterInfo.h"
+#include "llvm/Target/TargetFrameLowering.h"
+
+using namespace llvm;
+
+STATISTIC(NumAllocations, "Number of frame indices allocated into local block");
+STATISTIC(NumBaseRegisters, "Number of virtual frame base registers allocated");
+STATISTIC(NumReplacements, "Number of frame indices references replaced");
+
+namespace {
+ class FrameRef {
+ MachineBasicBlock::iterator MI; // Instr referencing the frame
+ int64_t LocalOffset; // Local offset of the frame idx referenced
+ public:
+ FrameRef(MachineBasicBlock::iterator I, int64_t Offset) :
+ MI(I), LocalOffset(Offset) {}
+ bool operator<(const FrameRef &RHS) const {
+ return LocalOffset < RHS.LocalOffset;
+ }
+ MachineBasicBlock::iterator getMachineInstr() { return MI; }
+ };
+
+ class LocalStackSlotPass: public MachineFunctionPass {
+ SmallVector<int64_t,16> LocalOffsets;
+
+ void AdjustStackOffset(MachineFrameInfo *MFI, int FrameIdx, int64_t &Offset,
+ bool StackGrowsDown, unsigned &MaxAlign);
+ void calculateFrameObjectOffsets(MachineFunction &Fn);
+ bool insertFrameReferenceRegisters(MachineFunction &Fn);
+ public:
+ static char ID; // Pass identification, replacement for typeid
+ explicit LocalStackSlotPass() : MachineFunctionPass(ID) { }
+ bool runOnMachineFunction(MachineFunction &MF);
+
+ virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+ AU.setPreservesCFG();
+ MachineFunctionPass::getAnalysisUsage(AU);
+ }
+
+ private:
+ };
+} // end anonymous namespace
+
+char LocalStackSlotPass::ID = 0;
+char &llvm::LocalStackSlotAllocationID = LocalStackSlotPass::ID;
+INITIALIZE_PASS(LocalStackSlotPass, "localstackalloc",
+ "Local Stack Slot Allocation", false, false)
+
+bool LocalStackSlotPass::runOnMachineFunction(MachineFunction &MF) {
+ MachineFrameInfo *MFI = MF.getFrameInfo();
+ const TargetRegisterInfo *TRI = MF.getTarget().getRegisterInfo();
+ unsigned LocalObjectCount = MFI->getObjectIndexEnd();
+
+ // If the target doesn't want/need this pass, or if there are no locals
+ // to consider, early exit.
+ if (!TRI->requiresVirtualBaseRegisters(MF) || LocalObjectCount == 0)
+ return true;
+
+ // Make sure we have enough space to store the local offsets.
+ LocalOffsets.resize(MFI->getObjectIndexEnd());
+
+ // Lay out the local blob.
+ calculateFrameObjectOffsets(MF);
+
+ // Insert virtual base registers to resolve frame index references.
+ bool UsedBaseRegs = insertFrameReferenceRegisters(MF);
+
+ // Tell MFI whether any base registers were allocated. PEI will only
+ // want to use the local block allocations from this pass if there were any.
+ // Otherwise, PEI can do a bit better job of getting the alignment right
+ // without a hole at the start since it knows the alignment of the stack
+ // at the start of local allocation, and this pass doesn't.
+ MFI->setUseLocalStackAllocationBlock(UsedBaseRegs);
+
+ return true;
+}
+
+/// AdjustStackOffset - Helper function used to adjust the stack frame offset.
+void LocalStackSlotPass::AdjustStackOffset(MachineFrameInfo *MFI,
+ int FrameIdx, int64_t &Offset,
+ bool StackGrowsDown,
+ unsigned &MaxAlign) {
+ // If the stack grows down, add the object size to find the lowest address.
+ if (StackGrowsDown)
+ Offset += MFI->getObjectSize(FrameIdx);
+
+ unsigned Align = MFI->getObjectAlignment(FrameIdx);
+
+ // If the alignment of this object is greater than that of the stack, then
+ // increase the stack alignment to match.
+ MaxAlign = std::max(MaxAlign, Align);
+
+ // Adjust to alignment boundary.
+ Offset = (Offset + Align - 1) / Align * Align;
+
+ int64_t LocalOffset = StackGrowsDown ? -Offset : Offset;
+ DEBUG(dbgs() << "Allocate FI(" << FrameIdx << ") to local offset "
+ << LocalOffset << "\n");
+ // Keep the offset available for base register allocation
+ LocalOffsets[FrameIdx] = LocalOffset;
+ // And tell MFI about it for PEI to use later
+ MFI->mapLocalFrameObject(FrameIdx, LocalOffset);
+
+ if (!StackGrowsDown)
+ Offset += MFI->getObjectSize(FrameIdx);
+
+ ++NumAllocations;
+}
+
+/// calculateFrameObjectOffsets - Calculate actual frame offsets for all of the
+/// abstract stack objects.
+///
+void LocalStackSlotPass::calculateFrameObjectOffsets(MachineFunction &Fn) {
+ // Loop over all of the stack objects, assigning sequential addresses...
+ MachineFrameInfo *MFI = Fn.getFrameInfo();
+ const TargetFrameLowering &TFI = *Fn.getTarget().getFrameLowering();
+ bool StackGrowsDown =
+ TFI.getStackGrowthDirection() == TargetFrameLowering::StackGrowsDown;
+ int64_t Offset = 0;
+ unsigned MaxAlign = 0;
+
+ // Make sure that the stack protector comes before the local variables on the
+ // stack.
+ SmallSet<int, 16> LargeStackObjs;
+ if (MFI->getStackProtectorIndex() >= 0) {
+ AdjustStackOffset(MFI, MFI->getStackProtectorIndex(), Offset,
+ StackGrowsDown, MaxAlign);
+
+ // Assign large stack objects first.
+ for (unsigned i = 0, e = MFI->getObjectIndexEnd(); i != e; ++i) {
+ if (MFI->isDeadObjectIndex(i))
+ continue;
+ if (MFI->getStackProtectorIndex() == (int)i)
+ continue;
+ if (!MFI->MayNeedStackProtector(i))
+ continue;
+
+ AdjustStackOffset(MFI, i, Offset, StackGrowsDown, MaxAlign);
+ LargeStackObjs.insert(i);
+ }
+ }
+
+ // Then assign frame offsets to stack objects that are not used to spill
+ // callee saved registers.
+ for (unsigned i = 0, e = MFI->getObjectIndexEnd(); i != e; ++i) {
+ if (MFI->isDeadObjectIndex(i))
+ continue;
+ if (MFI->getStackProtectorIndex() == (int)i)
+ continue;
+ if (LargeStackObjs.count(i))
+ continue;
+
+ AdjustStackOffset(MFI, i, Offset, StackGrowsDown, MaxAlign);
+ }
+
+ // Remember how big this blob of stack space is
+ MFI->setLocalFrameSize(Offset);
+ MFI->setLocalFrameMaxAlign(MaxAlign);
+}
+
+static inline bool
+lookupCandidateBaseReg(const SmallVector<std::pair<unsigned, int64_t>, 8> &Regs,
+ std::pair<unsigned, int64_t> &RegOffset,
+ int64_t FrameSizeAdjust,
+ int64_t LocalFrameOffset,
+ const MachineInstr *MI,
+ const TargetRegisterInfo *TRI) {
+ unsigned e = Regs.size();
+ for (unsigned i = 0; i < e; ++i) {
+ RegOffset = Regs[i];
+ // 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 - RegOffset.second;
+ if (TRI->isFrameOffsetLegal(MI, Offset))
+ return true;
+ }
+ return false;
+}
+
+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;
+
+ // A base register definition is a register + offset pair.
+ SmallVector<std::pair<unsigned, int64_t>, 8> BaseRegisters;
+
+ 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 instructions can't be out of range, so they don't need
+ // any updates.
+ if (MI->isDebugValue())
+ 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;
+ FrameReferenceInsns.
+ push_back(FrameRef(MI, LocalOffsets[MI->getOperand(i).getIndex()]));
+ break;
+ }
+ }
+ }
+ }
+
+ // Sort the frame references by local offset
+ array_pod_sort(FrameReferenceInsns.begin(), FrameReferenceInsns.end());
+
+ MachineBasicBlock *Entry = Fn.begin();
+
+ // Loop through the frame references and allocate for them as necessary.
+ for (int ref = 0, e = FrameReferenceInsns.size(); ref < e ; ++ref) {
+ MachineBasicBlock::iterator I =
+ FrameReferenceInsns[ref].getMachineInstr();
+ MachineInstr *MI = I;
+ for (unsigned idx = 0, e = MI->getNumOperands(); idx != e; ++idx) {
+ // Consider replacing all frame index operands that reference
+ // an object allocated in the local block.
+ if (MI->getOperand(idx).isFI()) {
+ int FrameIdx = MI->getOperand(idx).getIndex();
+
+ assert(MFI->isObjectPreAllocated(FrameIdx) &&
+ "Only pre-allocated locals expected!");
+
+ DEBUG(dbgs() << "Considering: " << *MI);
+ if (TRI->needsFrameBaseReg(MI, LocalOffsets[FrameIdx])) {
+ unsigned BaseReg = 0;
+ 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.
+ std::pair<unsigned, int64_t> RegOffset;
+ if (lookupCandidateBaseReg(BaseRegisters, RegOffset,
+ FrameSizeAdjust,
+ LocalOffsets[FrameIdx],
+ MI, TRI)) {
+ DEBUG(dbgs() << " Reusing base register " <<
+ RegOffset.first << "\n");
+ // We found a register to reuse.
+ BaseReg = RegOffset.first;
+ Offset = FrameSizeAdjust + LocalOffsets[FrameIdx] -
+ RegOffset.second;
+ } else {
+ // No previously defined register was in range, so create a
+ // new one.
+ int64_t InstrOffset = TRI->getFrameIndexInstrOffset(MI, idx);
+ const TargetRegisterClass *RC = TRI->getPointerRegClass();
+ BaseReg = Fn.getRegInfo().createVirtualRegister(RC);
+
+ DEBUG(dbgs() << " Materializing base register " << BaseReg <<
+ " at frame local offset " <<
+ LocalOffsets[FrameIdx] + 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;
+
+ int64_t BaseOffset = FrameSizeAdjust + LocalOffsets[FrameIdx] +
+ InstrOffset;
+ BaseRegisters.push_back(
+ std::pair<unsigned, int64_t>(BaseReg, BaseOffset));
+ ++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;
+}
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