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 #include "llvm/CodeGen/Passes.h"
18 #include "llvm/ADT/STLExtras.h"
19 #include "llvm/ADT/SetVector.h"
20 #include "llvm/ADT/SmallSet.h"
21 #include "llvm/ADT/Statistic.h"
22 #include "llvm/CodeGen/MachineFrameInfo.h"
23 #include "llvm/CodeGen/MachineFunction.h"
24 #include "llvm/CodeGen/MachineFunctionPass.h"
25 #include "llvm/CodeGen/MachineRegisterInfo.h"
26 #include "llvm/CodeGen/StackProtector.h"
27 #include "llvm/IR/Constants.h"
28 #include "llvm/IR/DerivedTypes.h"
29 #include "llvm/IR/Instructions.h"
30 #include "llvm/IR/Intrinsics.h"
31 #include "llvm/IR/LLVMContext.h"
32 #include "llvm/IR/Module.h"
33 #include "llvm/Pass.h"
34 #include "llvm/Support/Debug.h"
35 #include "llvm/Support/ErrorHandling.h"
36 #include "llvm/Support/raw_ostream.h"
37 #include "llvm/Target/TargetFrameLowering.h"
38 #include "llvm/Target/TargetRegisterInfo.h"
39 #include "llvm/Target/TargetSubtargetInfo.h"
43 #define DEBUG_TYPE "localstackalloc"
45 STATISTIC(NumAllocations
, "Number of frame indices allocated into local block");
46 STATISTIC(NumBaseRegisters
, "Number of virtual frame base registers allocated");
47 STATISTIC(NumReplacements
, "Number of frame indices references replaced");
51 MachineBasicBlock::iterator MI
; // Instr referencing the frame
52 int64_t LocalOffset
; // Local offset of the frame idx referenced
53 int FrameIdx
; // The frame index
55 FrameRef(MachineBasicBlock::iterator I
, int64_t Offset
, int Idx
) :
56 MI(I
), LocalOffset(Offset
), FrameIdx(Idx
) {}
57 bool operator<(const FrameRef
&RHS
) const {
58 return LocalOffset
< RHS
.LocalOffset
;
60 MachineBasicBlock::iterator
getMachineInstr() const { return MI
; }
61 int64_t getLocalOffset() const { return LocalOffset
; }
62 int getFrameIndex() const { return FrameIdx
; }
65 class LocalStackSlotPass
: public MachineFunctionPass
{
66 SmallVector
<int64_t,16> LocalOffsets
;
67 /// StackObjSet - A set of stack object indexes
68 typedef SmallSetVector
<int, 8> StackObjSet
;
70 void AdjustStackOffset(MachineFrameInfo
*MFI
, int FrameIdx
, int64_t &Offset
,
71 bool StackGrowsDown
, unsigned &MaxAlign
);
72 void AssignProtectedObjSet(const StackObjSet
&UnassignedObjs
,
73 SmallSet
<int, 16> &ProtectedObjs
,
74 MachineFrameInfo
*MFI
, bool StackGrowsDown
,
75 int64_t &Offset
, unsigned &MaxAlign
);
76 void calculateFrameObjectOffsets(MachineFunction
&Fn
);
77 bool insertFrameReferenceRegisters(MachineFunction
&Fn
);
79 static char ID
; // Pass identification, replacement for typeid
80 explicit LocalStackSlotPass() : MachineFunctionPass(ID
) {
81 initializeLocalStackSlotPassPass(*PassRegistry::getPassRegistry());
83 bool runOnMachineFunction(MachineFunction
&MF
) override
;
85 void getAnalysisUsage(AnalysisUsage
&AU
) const override
{
87 AU
.addRequired
<StackProtector
>();
88 MachineFunctionPass::getAnalysisUsage(AU
);
93 } // end anonymous namespace
95 char LocalStackSlotPass::ID
= 0;
96 char &llvm::LocalStackSlotAllocationID
= LocalStackSlotPass::ID
;
97 INITIALIZE_PASS_BEGIN(LocalStackSlotPass
, "localstackalloc",
98 "Local Stack Slot Allocation", false, false)
99 INITIALIZE_PASS_DEPENDENCY(StackProtector
)
100 INITIALIZE_PASS_END(LocalStackSlotPass
, "localstackalloc",
101 "Local Stack Slot Allocation", false, false)
104 bool LocalStackSlotPass::runOnMachineFunction(MachineFunction
&MF
) {
105 MachineFrameInfo
*MFI
= MF
.getFrameInfo();
106 const TargetRegisterInfo
*TRI
= MF
.getSubtarget().getRegisterInfo();
107 unsigned LocalObjectCount
= MFI
->getObjectIndexEnd();
109 // If the target doesn't want/need this pass, or if there are no locals
110 // to consider, early exit.
111 if (!TRI
->requiresVirtualBaseRegisters(MF
) || LocalObjectCount
== 0)
114 // Make sure we have enough space to store the local offsets.
115 LocalOffsets
.resize(MFI
->getObjectIndexEnd());
117 // Lay out the local blob.
118 calculateFrameObjectOffsets(MF
);
120 // Insert virtual base registers to resolve frame index references.
121 bool UsedBaseRegs
= insertFrameReferenceRegisters(MF
);
123 // Tell MFI whether any base registers were allocated. PEI will only
124 // want to use the local block allocations from this pass if there were any.
125 // Otherwise, PEI can do a bit better job of getting the alignment right
126 // without a hole at the start since it knows the alignment of the stack
127 // at the start of local allocation, and this pass doesn't.
128 MFI
->setUseLocalStackAllocationBlock(UsedBaseRegs
);
133 /// AdjustStackOffset - Helper function used to adjust the stack frame offset.
134 void LocalStackSlotPass::AdjustStackOffset(MachineFrameInfo
*MFI
,
135 int FrameIdx
, int64_t &Offset
,
137 unsigned &MaxAlign
) {
138 // If the stack grows down, add the object size to find the lowest address.
140 Offset
+= MFI
->getObjectSize(FrameIdx
);
142 unsigned Align
= MFI
->getObjectAlignment(FrameIdx
);
144 // If the alignment of this object is greater than that of the stack, then
145 // increase the stack alignment to match.
146 MaxAlign
= std::max(MaxAlign
, Align
);
148 // Adjust to alignment boundary.
149 Offset
= (Offset
+ Align
- 1) / Align
* Align
;
151 int64_t LocalOffset
= StackGrowsDown
? -Offset
: Offset
;
152 DEBUG(dbgs() << "Allocate FI(" << FrameIdx
<< ") to local offset "
153 << LocalOffset
<< "\n");
154 // Keep the offset available for base register allocation
155 LocalOffsets
[FrameIdx
] = LocalOffset
;
156 // And tell MFI about it for PEI to use later
157 MFI
->mapLocalFrameObject(FrameIdx
, LocalOffset
);
160 Offset
+= MFI
->getObjectSize(FrameIdx
);
165 /// AssignProtectedObjSet - Helper function to assign large stack objects (i.e.,
166 /// those required to be close to the Stack Protector) to stack offsets.
167 void LocalStackSlotPass::AssignProtectedObjSet(const StackObjSet
&UnassignedObjs
,
168 SmallSet
<int, 16> &ProtectedObjs
,
169 MachineFrameInfo
*MFI
,
170 bool StackGrowsDown
, int64_t &Offset
,
171 unsigned &MaxAlign
) {
173 for (StackObjSet::const_iterator I
= UnassignedObjs
.begin(),
174 E
= UnassignedObjs
.end(); I
!= E
; ++I
) {
176 AdjustStackOffset(MFI
, i
, Offset
, StackGrowsDown
, MaxAlign
);
177 ProtectedObjs
.insert(i
);
181 /// calculateFrameObjectOffsets - Calculate actual frame offsets for all of the
182 /// abstract stack objects.
184 void LocalStackSlotPass::calculateFrameObjectOffsets(MachineFunction
&Fn
) {
185 // Loop over all of the stack objects, assigning sequential addresses...
186 MachineFrameInfo
*MFI
= Fn
.getFrameInfo();
187 const TargetFrameLowering
&TFI
= *Fn
.getSubtarget().getFrameLowering();
188 bool StackGrowsDown
=
189 TFI
.getStackGrowthDirection() == TargetFrameLowering::StackGrowsDown
;
191 unsigned MaxAlign
= 0;
192 StackProtector
*SP
= &getAnalysis
<StackProtector
>();
194 // Make sure that the stack protector comes before the local variables on the
196 SmallSet
<int, 16> ProtectedObjs
;
197 if (MFI
->getStackProtectorIndex() >= 0) {
198 StackObjSet LargeArrayObjs
;
199 StackObjSet SmallArrayObjs
;
200 StackObjSet AddrOfObjs
;
202 AdjustStackOffset(MFI
, MFI
->getStackProtectorIndex(), Offset
,
203 StackGrowsDown
, MaxAlign
);
205 // Assign large stack objects first.
206 for (unsigned i
= 0, e
= MFI
->getObjectIndexEnd(); i
!= e
; ++i
) {
207 if (MFI
->isDeadObjectIndex(i
))
209 if (MFI
->getStackProtectorIndex() == (int)i
)
212 switch (SP
->getSSPLayout(MFI
->getObjectAllocation(i
))) {
213 case StackProtector::SSPLK_None
:
215 case StackProtector::SSPLK_SmallArray
:
216 SmallArrayObjs
.insert(i
);
218 case StackProtector::SSPLK_AddrOf
:
219 AddrOfObjs
.insert(i
);
221 case StackProtector::SSPLK_LargeArray
:
222 LargeArrayObjs
.insert(i
);
225 llvm_unreachable("Unexpected SSPLayoutKind.");
228 AssignProtectedObjSet(LargeArrayObjs
, ProtectedObjs
, MFI
, StackGrowsDown
,
230 AssignProtectedObjSet(SmallArrayObjs
, ProtectedObjs
, MFI
, StackGrowsDown
,
232 AssignProtectedObjSet(AddrOfObjs
, ProtectedObjs
, MFI
, StackGrowsDown
,
236 // Then assign frame offsets to stack objects that are not used to spill
237 // callee saved registers.
238 for (unsigned i
= 0, e
= MFI
->getObjectIndexEnd(); i
!= e
; ++i
) {
239 if (MFI
->isDeadObjectIndex(i
))
241 if (MFI
->getStackProtectorIndex() == (int)i
)
243 if (ProtectedObjs
.count(i
))
246 AdjustStackOffset(MFI
, i
, Offset
, StackGrowsDown
, MaxAlign
);
249 // Remember how big this blob of stack space is
250 MFI
->setLocalFrameSize(Offset
);
251 MFI
->setLocalFrameMaxAlign(MaxAlign
);
255 lookupCandidateBaseReg(int64_t BaseOffset
,
256 int64_t FrameSizeAdjust
,
257 int64_t LocalFrameOffset
,
258 const MachineInstr
*MI
,
259 const TargetRegisterInfo
*TRI
) {
260 // Check if the relative offset from the where the base register references
261 // to the target address is in range for the instruction.
262 int64_t Offset
= FrameSizeAdjust
+ LocalFrameOffset
- BaseOffset
;
263 return TRI
->isFrameOffsetLegal(MI
, Offset
);
266 bool LocalStackSlotPass::insertFrameReferenceRegisters(MachineFunction
&Fn
) {
267 // Scan the function's instructions looking for frame index references.
268 // For each, ask the target if it wants a virtual base register for it
269 // based on what we can tell it about where the local will end up in the
270 // stack frame. If it wants one, re-use a suitable one we've previously
271 // allocated, or if there isn't one that fits the bill, allocate a new one
272 // and ask the target to create a defining instruction for it.
273 bool UsedBaseReg
= false;
275 MachineFrameInfo
*MFI
= Fn
.getFrameInfo();
276 const TargetRegisterInfo
*TRI
= Fn
.getSubtarget().getRegisterInfo();
277 const TargetFrameLowering
&TFI
= *Fn
.getSubtarget().getFrameLowering();
278 bool StackGrowsDown
=
279 TFI
.getStackGrowthDirection() == TargetFrameLowering::StackGrowsDown
;
281 // Collect all of the instructions in the block that reference
282 // a frame index. Also store the frame index referenced to ease later
283 // lookup. (For any insn that has more than one FI reference, we arbitrarily
284 // choose the first one).
285 SmallVector
<FrameRef
, 64> FrameReferenceInsns
;
287 for (MachineFunction::iterator BB
= Fn
.begin(), E
= Fn
.end(); BB
!= E
; ++BB
) {
288 for (MachineBasicBlock::iterator I
= BB
->begin(); I
!= BB
->end(); ++I
) {
289 MachineInstr
*MI
= I
;
291 // Debug value, stackmap and patchpoint instructions can't be out of
292 // range, so they don't need any updates.
293 if (MI
->isDebugValue() ||
294 MI
->getOpcode() == TargetOpcode::STATEPOINT
||
295 MI
->getOpcode() == TargetOpcode::STACKMAP
||
296 MI
->getOpcode() == TargetOpcode::PATCHPOINT
)
299 // For now, allocate the base register(s) within the basic block
300 // where they're used, and don't try to keep them around outside
301 // of that. It may be beneficial to try sharing them more broadly
302 // than that, but the increased register pressure makes that a
303 // tricky thing to balance. Investigate if re-materializing these
305 for (unsigned i
= 0, e
= MI
->getNumOperands(); i
!= e
; ++i
) {
306 // Consider replacing all frame index operands that reference
307 // an object allocated in the local block.
308 if (MI
->getOperand(i
).isFI()) {
309 // Don't try this with values not in the local block.
310 if (!MFI
->isObjectPreAllocated(MI
->getOperand(i
).getIndex()))
312 int Idx
= MI
->getOperand(i
).getIndex();
313 int64_t LocalOffset
= LocalOffsets
[Idx
];
314 if (!TRI
->needsFrameBaseReg(MI
, LocalOffset
))
317 push_back(FrameRef(MI
, LocalOffset
, Idx
));
324 // Sort the frame references by local offset
325 array_pod_sort(FrameReferenceInsns
.begin(), FrameReferenceInsns
.end());
327 MachineBasicBlock
*Entry
= Fn
.begin();
329 unsigned BaseReg
= 0;
330 int64_t BaseOffset
= 0;
332 // Loop through the frame references and allocate for them as necessary.
333 for (int ref
= 0, e
= FrameReferenceInsns
.size(); ref
< e
; ++ref
) {
334 FrameRef
&FR
= FrameReferenceInsns
[ref
];
335 MachineBasicBlock::iterator I
= FR
.getMachineInstr();
336 MachineInstr
*MI
= I
;
337 int64_t LocalOffset
= FR
.getLocalOffset();
338 int FrameIdx
= FR
.getFrameIndex();
339 assert(MFI
->isObjectPreAllocated(FrameIdx
) &&
340 "Only pre-allocated locals expected!");
342 DEBUG(dbgs() << "Considering: " << *MI
);
345 for (unsigned f
= MI
->getNumOperands(); idx
!= f
; ++idx
) {
346 if (!MI
->getOperand(idx
).isFI())
349 if (FrameIdx
== I
->getOperand(idx
).getIndex())
353 assert(idx
< MI
->getNumOperands() && "Cannot find FI operand");
356 int64_t FrameSizeAdjust
= StackGrowsDown
? MFI
->getLocalFrameSize() : 0;
358 DEBUG(dbgs() << " Replacing FI in: " << *MI
);
360 // If we have a suitable base register available, use it; otherwise
361 // create a new one. Note that any offset encoded in the
362 // instruction itself will be taken into account by the target,
363 // so we don't have to adjust for it here when reusing a base
365 if (UsedBaseReg
&& lookupCandidateBaseReg(BaseOffset
, FrameSizeAdjust
,
366 LocalOffset
, MI
, TRI
)) {
367 DEBUG(dbgs() << " Reusing base register " << BaseReg
<< "\n");
368 // We found a register to reuse.
369 Offset
= FrameSizeAdjust
+ LocalOffset
- BaseOffset
;
371 // No previously defined register was in range, so create a // new one.
373 int64_t InstrOffset
= TRI
->getFrameIndexInstrOffset(MI
, idx
);
375 int64_t PrevBaseOffset
= BaseOffset
;
376 BaseOffset
= FrameSizeAdjust
+ LocalOffset
+ InstrOffset
;
378 // We'd like to avoid creating single-use virtual base registers.
379 // Because the FrameRefs are in sorted order, and we've already
380 // processed all FrameRefs before this one, just check whether or not
381 // the next FrameRef will be able to reuse this new register. If not,
382 // then don't bother creating it.
384 !lookupCandidateBaseReg(
385 BaseOffset
, FrameSizeAdjust
,
386 FrameReferenceInsns
[ref
+ 1].getLocalOffset(),
387 FrameReferenceInsns
[ref
+ 1].getMachineInstr(), TRI
)) {
388 BaseOffset
= PrevBaseOffset
;
392 const MachineFunction
*MF
= MI
->getParent()->getParent();
393 const TargetRegisterClass
*RC
= TRI
->getPointerRegClass(*MF
);
394 BaseReg
= Fn
.getRegInfo().createVirtualRegister(RC
);
396 DEBUG(dbgs() << " Materializing base register " << BaseReg
<<
397 " at frame local offset " << LocalOffset
+ InstrOffset
<< "\n");
399 // Tell the target to insert the instruction to initialize
400 // the base register.
401 // MachineBasicBlock::iterator InsertionPt = Entry->begin();
402 TRI
->materializeFrameBaseRegister(Entry
, BaseReg
, FrameIdx
,
405 // The base register already includes any offset specified
406 // by the instruction, so account for that so it doesn't get
408 Offset
= -InstrOffset
;
413 assert(BaseReg
!= 0 && "Unable to allocate virtual base register!");
415 // Modify the instruction to use the new base register rather
416 // than the frame index operand.
417 TRI
->resolveFrameIndex(*I
, BaseReg
, Offset
);
418 DEBUG(dbgs() << "Resolved: " << *MI
);