1 //===- LocalStackSlotAllocation.cpp - Pre-allocate locals to stack slots --===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This pass assigns local frame indices to stack slots relative to one another
11 // and allocates additional base registers to access them when the target
12 // estimates they are likely to be out of range of stack pointer and frame
13 // pointer relative addressing.
15 //===----------------------------------------------------------------------===//
17 #define DEBUG_TYPE "localstackalloc"
18 #include "llvm/CodeGen/Passes.h"
19 #include "llvm/ADT/STLExtras.h"
20 #include "llvm/ADT/SetVector.h"
21 #include "llvm/ADT/SmallSet.h"
22 #include "llvm/ADT/Statistic.h"
23 #include "llvm/CodeGen/MachineFrameInfo.h"
24 #include "llvm/CodeGen/MachineFunction.h"
25 #include "llvm/CodeGen/MachineFunctionPass.h"
26 #include "llvm/CodeGen/MachineRegisterInfo.h"
27 #include "llvm/CodeGen/StackProtector.h"
28 #include "llvm/IR/Constants.h"
29 #include "llvm/IR/DerivedTypes.h"
30 #include "llvm/IR/Instructions.h"
31 #include "llvm/IR/Intrinsics.h"
32 #include "llvm/IR/LLVMContext.h"
33 #include "llvm/IR/Module.h"
34 #include "llvm/Pass.h"
35 #include "llvm/Support/Debug.h"
36 #include "llvm/Support/ErrorHandling.h"
37 #include "llvm/Support/raw_ostream.h"
38 #include "llvm/Target/TargetFrameLowering.h"
39 #include "llvm/Target/TargetRegisterInfo.h"
43 STATISTIC(NumAllocations, "Number of frame indices allocated into local block");
44 STATISTIC(NumBaseRegisters, "Number of virtual frame base registers allocated");
45 STATISTIC(NumReplacements, "Number of frame indices references replaced");
49 MachineBasicBlock::iterator MI; // Instr referencing the frame
50 int64_t LocalOffset; // Local offset of the frame idx referenced
51 int FrameIdx; // The frame index
53 FrameRef(MachineBasicBlock::iterator I, int64_t Offset, int Idx) :
54 MI(I), LocalOffset(Offset), FrameIdx(Idx) {}
55 bool operator<(const FrameRef &RHS) const {
56 return LocalOffset < RHS.LocalOffset;
58 MachineBasicBlock::iterator getMachineInstr() const { return MI; }
59 int64_t getLocalOffset() const { return LocalOffset; }
60 int getFrameIndex() const { return FrameIdx; }
63 class LocalStackSlotPass: public MachineFunctionPass {
64 SmallVector<int64_t,16> LocalOffsets;
65 /// StackObjSet - A set of stack object indexes
66 typedef SmallSetVector<int, 8> StackObjSet;
68 void AdjustStackOffset(MachineFrameInfo *MFI, int FrameIdx, int64_t &Offset,
69 bool StackGrowsDown, unsigned &MaxAlign);
70 void AssignProtectedObjSet(const StackObjSet &UnassignedObjs,
71 SmallSet<int, 16> &ProtectedObjs,
72 MachineFrameInfo *MFI, bool StackGrowsDown,
73 int64_t &Offset, unsigned &MaxAlign);
74 void calculateFrameObjectOffsets(MachineFunction &Fn);
75 bool insertFrameReferenceRegisters(MachineFunction &Fn);
77 static char ID; // Pass identification, replacement for typeid
78 explicit LocalStackSlotPass() : MachineFunctionPass(ID) {
79 initializeLocalStackSlotPassPass(*PassRegistry::getPassRegistry());
81 bool runOnMachineFunction(MachineFunction &MF);
83 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
85 AU.addRequired<StackProtector>();
86 MachineFunctionPass::getAnalysisUsage(AU);
91 } // end anonymous namespace
93 char LocalStackSlotPass::ID = 0;
94 char &llvm::LocalStackSlotAllocationID = LocalStackSlotPass::ID;
95 INITIALIZE_PASS_BEGIN(LocalStackSlotPass, "localstackalloc",
96 "Local Stack Slot Allocation", false, false)
97 INITIALIZE_PASS_DEPENDENCY(StackProtector)
98 INITIALIZE_PASS_END(LocalStackSlotPass, "localstackalloc",
99 "Local Stack Slot Allocation", false, false)
102 bool LocalStackSlotPass::runOnMachineFunction(MachineFunction &MF) {
103 MachineFrameInfo *MFI = MF.getFrameInfo();
104 const TargetRegisterInfo *TRI = MF.getTarget().getRegisterInfo();
105 unsigned LocalObjectCount = MFI->getObjectIndexEnd();
107 // If the target doesn't want/need this pass, or if there are no locals
108 // to consider, early exit.
109 if (!TRI->requiresVirtualBaseRegisters(MF) || LocalObjectCount == 0)
112 // Make sure we have enough space to store the local offsets.
113 LocalOffsets.resize(MFI->getObjectIndexEnd());
115 // Lay out the local blob.
116 calculateFrameObjectOffsets(MF);
118 // Insert virtual base registers to resolve frame index references.
119 bool UsedBaseRegs = insertFrameReferenceRegisters(MF);
121 // Tell MFI whether any base registers were allocated. PEI will only
122 // want to use the local block allocations from this pass if there were any.
123 // Otherwise, PEI can do a bit better job of getting the alignment right
124 // without a hole at the start since it knows the alignment of the stack
125 // at the start of local allocation, and this pass doesn't.
126 MFI->setUseLocalStackAllocationBlock(UsedBaseRegs);
131 /// AdjustStackOffset - Helper function used to adjust the stack frame offset.
132 void LocalStackSlotPass::AdjustStackOffset(MachineFrameInfo *MFI,
133 int FrameIdx, int64_t &Offset,
135 unsigned &MaxAlign) {
136 // If the stack grows down, add the object size to find the lowest address.
138 Offset += MFI->getObjectSize(FrameIdx);
140 unsigned Align = MFI->getObjectAlignment(FrameIdx);
142 // If the alignment of this object is greater than that of the stack, then
143 // increase the stack alignment to match.
144 MaxAlign = std::max(MaxAlign, Align);
146 // Adjust to alignment boundary.
147 Offset = (Offset + Align - 1) / Align * Align;
149 int64_t LocalOffset = StackGrowsDown ? -Offset : Offset;
150 DEBUG(dbgs() << "Allocate FI(" << FrameIdx << ") to local offset "
151 << LocalOffset << "\n");
152 // Keep the offset available for base register allocation
153 LocalOffsets[FrameIdx] = LocalOffset;
154 // And tell MFI about it for PEI to use later
155 MFI->mapLocalFrameObject(FrameIdx, LocalOffset);
158 Offset += MFI->getObjectSize(FrameIdx);
163 /// AssignProtectedObjSet - Helper function to assign large stack objects (i.e.,
164 /// those required to be close to the Stack Protector) to stack offsets.
165 void LocalStackSlotPass::AssignProtectedObjSet(const StackObjSet &UnassignedObjs,
166 SmallSet<int, 16> &ProtectedObjs,
167 MachineFrameInfo *MFI,
168 bool StackGrowsDown, int64_t &Offset,
169 unsigned &MaxAlign) {
171 for (StackObjSet::const_iterator I = UnassignedObjs.begin(),
172 E = UnassignedObjs.end(); I != E; ++I) {
174 AdjustStackOffset(MFI, i, Offset, StackGrowsDown, MaxAlign);
175 ProtectedObjs.insert(i);
179 /// calculateFrameObjectOffsets - Calculate actual frame offsets for all of the
180 /// abstract stack objects.
182 void LocalStackSlotPass::calculateFrameObjectOffsets(MachineFunction &Fn) {
183 // Loop over all of the stack objects, assigning sequential addresses...
184 MachineFrameInfo *MFI = Fn.getFrameInfo();
185 const TargetFrameLowering &TFI = *Fn.getTarget().getFrameLowering();
186 bool StackGrowsDown =
187 TFI.getStackGrowthDirection() == TargetFrameLowering::StackGrowsDown;
189 unsigned MaxAlign = 0;
190 StackProtector *SP = &getAnalysis<StackProtector>();
192 // Make sure that the stack protector comes before the local variables on the
194 SmallSet<int, 16> ProtectedObjs;
195 if (MFI->getStackProtectorIndex() >= 0) {
196 StackObjSet LargeArrayObjs;
197 StackObjSet SmallArrayObjs;
198 StackObjSet AddrOfObjs;
200 AdjustStackOffset(MFI, MFI->getStackProtectorIndex(), Offset,
201 StackGrowsDown, MaxAlign);
203 // Assign large stack objects first.
204 for (unsigned i = 0, e = MFI->getObjectIndexEnd(); i != e; ++i) {
205 if (MFI->isDeadObjectIndex(i))
207 if (MFI->getStackProtectorIndex() == (int)i)
210 switch (SP->getSSPLayout(MFI->getObjectAllocation(i))) {
211 case StackProtector::SSPLK_None:
213 case StackProtector::SSPLK_SmallArray:
214 SmallArrayObjs.insert(i);
216 case StackProtector::SSPLK_AddrOf:
217 AddrOfObjs.insert(i);
219 case StackProtector::SSPLK_LargeArray:
220 LargeArrayObjs.insert(i);
223 llvm_unreachable("Unexpected SSPLayoutKind.");
226 AssignProtectedObjSet(LargeArrayObjs, ProtectedObjs, MFI, StackGrowsDown,
228 AssignProtectedObjSet(SmallArrayObjs, ProtectedObjs, MFI, StackGrowsDown,
230 AssignProtectedObjSet(AddrOfObjs, ProtectedObjs, MFI, StackGrowsDown,
234 // Then assign frame offsets to stack objects that are not used to spill
235 // callee saved registers.
236 for (unsigned i = 0, e = MFI->getObjectIndexEnd(); i != e; ++i) {
237 if (MFI->isDeadObjectIndex(i))
239 if (MFI->getStackProtectorIndex() == (int)i)
241 if (ProtectedObjs.count(i))
244 AdjustStackOffset(MFI, i, Offset, StackGrowsDown, MaxAlign);
247 // Remember how big this blob of stack space is
248 MFI->setLocalFrameSize(Offset);
249 MFI->setLocalFrameMaxAlign(MaxAlign);
253 lookupCandidateBaseReg(int64_t BaseOffset,
254 int64_t FrameSizeAdjust,
255 int64_t LocalFrameOffset,
256 const MachineInstr *MI,
257 const TargetRegisterInfo *TRI) {
258 // Check if the relative offset from the where the base register references
259 // to the target address is in range for the instruction.
260 int64_t Offset = FrameSizeAdjust + LocalFrameOffset - BaseOffset;
261 return TRI->isFrameOffsetLegal(MI, Offset);
264 bool LocalStackSlotPass::insertFrameReferenceRegisters(MachineFunction &Fn) {
265 // Scan the function's instructions looking for frame index references.
266 // For each, ask the target if it wants a virtual base register for it
267 // based on what we can tell it about where the local will end up in the
268 // stack frame. If it wants one, re-use a suitable one we've previously
269 // allocated, or if there isn't one that fits the bill, allocate a new one
270 // and ask the target to create a defining instruction for it.
271 bool UsedBaseReg = false;
273 MachineFrameInfo *MFI = Fn.getFrameInfo();
274 const TargetRegisterInfo *TRI = Fn.getTarget().getRegisterInfo();
275 const TargetFrameLowering &TFI = *Fn.getTarget().getFrameLowering();
276 bool StackGrowsDown =
277 TFI.getStackGrowthDirection() == TargetFrameLowering::StackGrowsDown;
279 // Collect all of the instructions in the block that reference
280 // a frame index. Also store the frame index referenced to ease later
281 // lookup. (For any insn that has more than one FI reference, we arbitrarily
282 // choose the first one).
283 SmallVector<FrameRef, 64> FrameReferenceInsns;
285 for (MachineFunction::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB) {
286 for (MachineBasicBlock::iterator I = BB->begin(); I != BB->end(); ++I) {
287 MachineInstr *MI = I;
289 // Debug value, stackmap and patchpoint instructions can't be out of
290 // range, so they don't need any updates.
291 if (MI->isDebugValue() ||
292 MI->getOpcode() == TargetOpcode::STACKMAP ||
293 MI->getOpcode() == TargetOpcode::PATCHPOINT)
296 // For now, allocate the base register(s) within the basic block
297 // where they're used, and don't try to keep them around outside
298 // of that. It may be beneficial to try sharing them more broadly
299 // than that, but the increased register pressure makes that a
300 // tricky thing to balance. Investigate if re-materializing these
302 for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
303 // Consider replacing all frame index operands that reference
304 // an object allocated in the local block.
305 if (MI->getOperand(i).isFI()) {
306 // Don't try this with values not in the local block.
307 if (!MFI->isObjectPreAllocated(MI->getOperand(i).getIndex()))
309 int Idx = MI->getOperand(i).getIndex();
310 int64_t LocalOffset = LocalOffsets[Idx];
311 if (!TRI->needsFrameBaseReg(MI, LocalOffset))
314 push_back(FrameRef(MI, LocalOffset, Idx));
321 // Sort the frame references by local offset
322 array_pod_sort(FrameReferenceInsns.begin(), FrameReferenceInsns.end());
324 MachineBasicBlock *Entry = Fn.begin();
326 unsigned BaseReg = 0;
327 int64_t BaseOffset = 0;
329 // Loop through the frame references and allocate for them as necessary.
330 for (int ref = 0, e = FrameReferenceInsns.size(); ref < e ; ++ref) {
331 FrameRef &FR = FrameReferenceInsns[ref];
332 MachineBasicBlock::iterator I = FR.getMachineInstr();
333 MachineInstr *MI = I;
334 int64_t LocalOffset = FR.getLocalOffset();
335 int FrameIdx = FR.getFrameIndex();
336 assert(MFI->isObjectPreAllocated(FrameIdx) &&
337 "Only pre-allocated locals expected!");
339 DEBUG(dbgs() << "Considering: " << *MI);
342 for (unsigned f = MI->getNumOperands(); idx != f; ++idx) {
343 if (!MI->getOperand(idx).isFI())
346 if (FrameIdx == I->getOperand(idx).getIndex())
350 assert(idx < MI->getNumOperands() && "Cannot find FI operand");
353 int64_t FrameSizeAdjust = StackGrowsDown ? MFI->getLocalFrameSize() : 0;
355 DEBUG(dbgs() << " Replacing FI in: " << *MI);
357 // If we have a suitable base register available, use it; otherwise
358 // create a new one. Note that any offset encoded in the
359 // instruction itself will be taken into account by the target,
360 // so we don't have to adjust for it here when reusing a base
362 if (UsedBaseReg && lookupCandidateBaseReg(BaseOffset, FrameSizeAdjust,
363 LocalOffset, MI, TRI)) {
364 DEBUG(dbgs() << " Reusing base register " << BaseReg << "\n");
365 // We found a register to reuse.
366 Offset = FrameSizeAdjust + LocalOffset - BaseOffset;
368 // No previously defined register was in range, so create a // new one.
370 int64_t InstrOffset = TRI->getFrameIndexInstrOffset(MI, idx);
372 int64_t PrevBaseOffset = BaseOffset;
373 BaseOffset = FrameSizeAdjust + LocalOffset + InstrOffset;
375 // We'd like to avoid creating single-use virtual base registers.
376 // Because the FrameRefs are in sorted order, and we've already
377 // processed all FrameRefs before this one, just check whether or not
378 // the next FrameRef will be able to reuse this new register. If not,
379 // then don't bother creating it.
380 bool CanReuse = false;
381 for (int refn = ref + 1; refn < e; ++refn) {
382 FrameRef &FRN = FrameReferenceInsns[refn];
383 MachineBasicBlock::iterator J = FRN.getMachineInstr();
384 MachineInstr *MIN = J;
386 CanReuse = lookupCandidateBaseReg(BaseOffset, FrameSizeAdjust,
387 FRN.getLocalOffset(), MIN, TRI);
392 BaseOffset = PrevBaseOffset;
396 const MachineFunction *MF = MI->getParent()->getParent();
397 const TargetRegisterClass *RC = TRI->getPointerRegClass(*MF);
398 BaseReg = Fn.getRegInfo().createVirtualRegister(RC);
400 DEBUG(dbgs() << " Materializing base register " << BaseReg <<
401 " at frame local offset " << LocalOffset + InstrOffset << "\n");
403 // Tell the target to insert the instruction to initialize
404 // the base register.
405 // MachineBasicBlock::iterator InsertionPt = Entry->begin();
406 TRI->materializeFrameBaseRegister(Entry, BaseReg, FrameIdx,
409 // The base register already includes any offset specified
410 // by the instruction, so account for that so it doesn't get
412 Offset = -InstrOffset;
417 assert(BaseReg != 0 && "Unable to allocate virtual base register!");
419 // Modify the instruction to use the new base register rather
420 // than the frame index operand.
421 TRI->resolveFrameIndex(I, BaseReg, Offset);
422 DEBUG(dbgs() << "Resolved: " << *MI);