LLVM 19.0.0git
CalledValuePropagation.cpp
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1//===- CalledValuePropagation.cpp - Propagate called values -----*- C++ -*-===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9// This file implements a transformation that attaches !callees metadata to
10// indirect call sites. For a given call site, the metadata, if present,
11// indicates the set of functions the call site could possibly target at
12// run-time. This metadata is added to indirect call sites when the set of
13// possible targets can be determined by analysis and is known to be small. The
14// analysis driving the transformation is similar to constant propagation and
15// makes uses of the generic sparse propagation solver.
16//
17//===----------------------------------------------------------------------===//
18
22#include "llvm/IR/Constants.h"
23#include "llvm/IR/MDBuilder.h"
25#include "llvm/Transforms/IPO.h"
26
27using namespace llvm;
28
29#define DEBUG_TYPE "called-value-propagation"
30
31/// The maximum number of functions to track per lattice value. Once the number
32/// of functions a call site can possibly target exceeds this threshold, it's
33/// lattice value becomes overdefined. The number of possible lattice values is
34/// bounded by Ch(F, M), where F is the number of functions in the module and M
35/// is MaxFunctionsPerValue. As such, this value should be kept very small. We
36/// likely can't do anything useful for call sites with a large number of
37/// possible targets, anyway.
39 "cvp-max-functions-per-value", cl::Hidden, cl::init(4),
40 cl::desc("The maximum number of functions to track per lattice value"));
41
42namespace {
43/// To enable interprocedural analysis, we assign LLVM values to the following
44/// groups. The register group represents SSA registers, the return group
45/// represents the return values of functions, and the memory group represents
46/// in-memory values. An LLVM Value can technically be in more than one group.
47/// It's necessary to distinguish these groups so we can, for example, track a
48/// global variable separately from the value stored at its location.
49enum class IPOGrouping { Register, Return, Memory };
50
51/// Our LatticeKeys are PointerIntPairs composed of LLVM values and groupings.
52using CVPLatticeKey = PointerIntPair<Value *, 2, IPOGrouping>;
53
54/// The lattice value type used by our custom lattice function. It holds the
55/// lattice state, and a set of functions.
56class CVPLatticeVal {
57public:
58 /// The states of the lattice values. Only the FunctionSet state is
59 /// interesting. It indicates the set of functions to which an LLVM value may
60 /// refer.
61 enum CVPLatticeStateTy { Undefined, FunctionSet, Overdefined, Untracked };
62
63 /// Comparator for sorting the functions set. We want to keep the order
64 /// deterministic for testing, etc.
65 struct Compare {
66 bool operator()(const Function *LHS, const Function *RHS) const {
67 return LHS->getName() < RHS->getName();
68 }
69 };
70
71 CVPLatticeVal() = default;
72 CVPLatticeVal(CVPLatticeStateTy LatticeState) : LatticeState(LatticeState) {}
73 CVPLatticeVal(std::vector<Function *> &&Functions)
74 : LatticeState(FunctionSet), Functions(std::move(Functions)) {
75 assert(llvm::is_sorted(this->Functions, Compare()));
76 }
77
78 /// Get a reference to the functions held by this lattice value. The number
79 /// of functions will be zero for states other than FunctionSet.
80 const std::vector<Function *> &getFunctions() const {
81 return Functions;
82 }
83
84 /// Returns true if the lattice value is in the FunctionSet state.
85 bool isFunctionSet() const { return LatticeState == FunctionSet; }
86
87 bool operator==(const CVPLatticeVal &RHS) const {
88 return LatticeState == RHS.LatticeState && Functions == RHS.Functions;
89 }
90
91 bool operator!=(const CVPLatticeVal &RHS) const {
92 return LatticeState != RHS.LatticeState || Functions != RHS.Functions;
93 }
94
95private:
96 /// Holds the state this lattice value is in.
97 CVPLatticeStateTy LatticeState = Undefined;
98
99 /// Holds functions indicating the possible targets of call sites. This set
100 /// is empty for lattice values in the undefined, overdefined, and untracked
101 /// states. The maximum size of the set is controlled by
102 /// MaxFunctionsPerValue. Since most LLVM values are expected to be in
103 /// uninteresting states (i.e., overdefined), CVPLatticeVal objects should be
104 /// small and efficiently copyable.
105 // FIXME: This could be a TinyPtrVector and/or merge with LatticeState.
106 std::vector<Function *> Functions;
107};
108
109/// The custom lattice function used by the generic sparse propagation solver.
110/// It handles merging lattice values and computing new lattice values for
111/// constants, arguments, values returned from trackable functions, and values
112/// located in trackable global variables. It also computes the lattice values
113/// that change as a result of executing instructions.
114class CVPLatticeFunc
115 : public AbstractLatticeFunction<CVPLatticeKey, CVPLatticeVal> {
116public:
117 CVPLatticeFunc()
118 : AbstractLatticeFunction(CVPLatticeVal(CVPLatticeVal::Undefined),
119 CVPLatticeVal(CVPLatticeVal::Overdefined),
120 CVPLatticeVal(CVPLatticeVal::Untracked)) {}
121
122 /// Compute and return a CVPLatticeVal for the given CVPLatticeKey.
123 CVPLatticeVal ComputeLatticeVal(CVPLatticeKey Key) override {
124 switch (Key.getInt()) {
125 case IPOGrouping::Register:
126 if (isa<Instruction>(Key.getPointer())) {
127 return getUndefVal();
128 } else if (auto *A = dyn_cast<Argument>(Key.getPointer())) {
129 if (canTrackArgumentsInterprocedurally(A->getParent()))
130 return getUndefVal();
131 } else if (auto *C = dyn_cast<Constant>(Key.getPointer())) {
132 return computeConstant(C);
133 }
134 return getOverdefinedVal();
135 case IPOGrouping::Memory:
136 case IPOGrouping::Return:
137 if (auto *GV = dyn_cast<GlobalVariable>(Key.getPointer())) {
139 return computeConstant(GV->getInitializer());
140 } else if (auto *F = cast<Function>(Key.getPointer()))
142 return getUndefVal();
143 }
144 return getOverdefinedVal();
145 }
146
147 /// Merge the two given lattice values. The interesting cases are merging two
148 /// FunctionSet values and a FunctionSet value with an Undefined value. For
149 /// these cases, we simply union the function sets. If the size of the union
150 /// is greater than the maximum functions we track, the merged value is
151 /// overdefined.
152 CVPLatticeVal MergeValues(CVPLatticeVal X, CVPLatticeVal Y) override {
153 if (X == getOverdefinedVal() || Y == getOverdefinedVal())
154 return getOverdefinedVal();
155 if (X == getUndefVal() && Y == getUndefVal())
156 return getUndefVal();
157 std::vector<Function *> Union;
158 std::set_union(X.getFunctions().begin(), X.getFunctions().end(),
159 Y.getFunctions().begin(), Y.getFunctions().end(),
160 std::back_inserter(Union), CVPLatticeVal::Compare{});
161 if (Union.size() > MaxFunctionsPerValue)
162 return getOverdefinedVal();
163 return CVPLatticeVal(std::move(Union));
164 }
165
166 /// Compute the lattice values that change as a result of executing the given
167 /// instruction. The changed values are stored in \p ChangedValues. We handle
168 /// just a few kinds of instructions since we're only propagating values that
169 /// can be called.
173 switch (I.getOpcode()) {
174 case Instruction::Call:
175 case Instruction::Invoke:
176 return visitCallBase(cast<CallBase>(I), ChangedValues, SS);
177 case Instruction::Load:
178 return visitLoad(*cast<LoadInst>(&I), ChangedValues, SS);
179 case Instruction::Ret:
180 return visitReturn(*cast<ReturnInst>(&I), ChangedValues, SS);
181 case Instruction::Select:
182 return visitSelect(*cast<SelectInst>(&I), ChangedValues, SS);
183 case Instruction::Store:
184 return visitStore(*cast<StoreInst>(&I), ChangedValues, SS);
185 default:
186 return visitInst(I, ChangedValues, SS);
187 }
188 }
189
190 /// Print the given CVPLatticeVal to the specified stream.
191 void PrintLatticeVal(CVPLatticeVal LV, raw_ostream &OS) override {
192 if (LV == getUndefVal())
193 OS << "Undefined ";
194 else if (LV == getOverdefinedVal())
195 OS << "Overdefined";
196 else if (LV == getUntrackedVal())
197 OS << "Untracked ";
198 else
199 OS << "FunctionSet";
200 }
201
202 /// Print the given CVPLatticeKey to the specified stream.
203 void PrintLatticeKey(CVPLatticeKey Key, raw_ostream &OS) override {
204 if (Key.getInt() == IPOGrouping::Register)
205 OS << "<reg> ";
206 else if (Key.getInt() == IPOGrouping::Memory)
207 OS << "<mem> ";
208 else if (Key.getInt() == IPOGrouping::Return)
209 OS << "<ret> ";
210 if (isa<Function>(Key.getPointer()))
211 OS << Key.getPointer()->getName();
212 else
213 OS << *Key.getPointer();
214 }
215
216 /// We collect a set of indirect calls when visiting call sites. This method
217 /// returns a reference to that set.
218 SmallPtrSetImpl<CallBase *> &getIndirectCalls() { return IndirectCalls; }
219
220private:
221 /// Holds the indirect calls we encounter during the analysis. We will attach
222 /// metadata to these calls after the analysis indicating the functions the
223 /// calls can possibly target.
224 SmallPtrSet<CallBase *, 32> IndirectCalls;
225
226 /// Compute a new lattice value for the given constant. The constant, after
227 /// stripping any pointer casts, should be a Function. We ignore null
228 /// pointers as an optimization, since calling these values is undefined
229 /// behavior.
230 CVPLatticeVal computeConstant(Constant *C) {
231 if (isa<ConstantPointerNull>(C))
232 return CVPLatticeVal(CVPLatticeVal::FunctionSet);
233 if (auto *F = dyn_cast<Function>(C->stripPointerCasts()))
234 return CVPLatticeVal({F});
235 return getOverdefinedVal();
236 }
237
238 /// Handle return instructions. The function's return state is the merge of
239 /// the returned value state and the function's return state.
240 void visitReturn(ReturnInst &I,
243 Function *F = I.getParent()->getParent();
244 if (F->getReturnType()->isVoidTy())
245 return;
246 auto RegI = CVPLatticeKey(I.getReturnValue(), IPOGrouping::Register);
247 auto RetF = CVPLatticeKey(F, IPOGrouping::Return);
248 ChangedValues[RetF] =
249 MergeValues(SS.getValueState(RegI), SS.getValueState(RetF));
250 }
251
252 /// Handle call sites. The state of a called function's formal arguments is
253 /// the merge of the argument state with the call sites corresponding actual
254 /// argument state. The call site state is the merge of the call site state
255 /// with the returned value state of the called function.
256 void visitCallBase(CallBase &CB,
260 auto RegI = CVPLatticeKey(&CB, IPOGrouping::Register);
261
262 // If this is an indirect call, save it so we can quickly revisit it when
263 // attaching metadata.
264 if (!F)
265 IndirectCalls.insert(&CB);
266
267 // If we can't track the function's return values, there's nothing to do.
269 // Void return, No need to create and update CVPLattice state as no one
270 // can use it.
271 if (CB.getType()->isVoidTy())
272 return;
273 ChangedValues[RegI] = getOverdefinedVal();
274 return;
275 }
276
277 // Inform the solver that the called function is executable, and perform
278 // the merges for the arguments and return value.
279 SS.MarkBlockExecutable(&F->front());
280 auto RetF = CVPLatticeKey(F, IPOGrouping::Return);
281 for (Argument &A : F->args()) {
282 auto RegFormal = CVPLatticeKey(&A, IPOGrouping::Register);
283 auto RegActual =
284 CVPLatticeKey(CB.getArgOperand(A.getArgNo()), IPOGrouping::Register);
285 ChangedValues[RegFormal] =
286 MergeValues(SS.getValueState(RegFormal), SS.getValueState(RegActual));
287 }
288
289 // Void return, No need to create and update CVPLattice state as no one can
290 // use it.
291 if (CB.getType()->isVoidTy())
292 return;
293
294 ChangedValues[RegI] =
295 MergeValues(SS.getValueState(RegI), SS.getValueState(RetF));
296 }
297
298 /// Handle select instructions. The select instruction state is the merge the
299 /// true and false value states.
300 void visitSelect(SelectInst &I,
303 auto RegI = CVPLatticeKey(&I, IPOGrouping::Register);
304 auto RegT = CVPLatticeKey(I.getTrueValue(), IPOGrouping::Register);
305 auto RegF = CVPLatticeKey(I.getFalseValue(), IPOGrouping::Register);
306 ChangedValues[RegI] =
307 MergeValues(SS.getValueState(RegT), SS.getValueState(RegF));
308 }
309
310 /// Handle load instructions. If the pointer operand of the load is a global
311 /// variable, we attempt to track the value. The loaded value state is the
312 /// merge of the loaded value state with the global variable state.
313 void visitLoad(LoadInst &I,
316 auto RegI = CVPLatticeKey(&I, IPOGrouping::Register);
317 if (auto *GV = dyn_cast<GlobalVariable>(I.getPointerOperand())) {
318 auto MemGV = CVPLatticeKey(GV, IPOGrouping::Memory);
319 ChangedValues[RegI] =
320 MergeValues(SS.getValueState(RegI), SS.getValueState(MemGV));
321 } else {
322 ChangedValues[RegI] = getOverdefinedVal();
323 }
324 }
325
326 /// Handle store instructions. If the pointer operand of the store is a
327 /// global variable, we attempt to track the value. The global variable state
328 /// is the merge of the stored value state with the global variable state.
329 void visitStore(StoreInst &I,
332 auto *GV = dyn_cast<GlobalVariable>(I.getPointerOperand());
333 if (!GV)
334 return;
335 auto RegI = CVPLatticeKey(I.getValueOperand(), IPOGrouping::Register);
336 auto MemGV = CVPLatticeKey(GV, IPOGrouping::Memory);
337 ChangedValues[MemGV] =
338 MergeValues(SS.getValueState(RegI), SS.getValueState(MemGV));
339 }
340
341 /// Handle all other instructions. All other instructions are marked
342 /// overdefined.
343 void visitInst(Instruction &I,
346 // Simply bail if this instruction has no user.
347 if (I.use_empty())
348 return;
349 auto RegI = CVPLatticeKey(&I, IPOGrouping::Register);
350 ChangedValues[RegI] = getOverdefinedVal();
351 }
352};
353} // namespace
354
355namespace llvm {
356/// A specialization of LatticeKeyInfo for CVPLatticeKeys. The generic solver
357/// must translate between LatticeKeys and LLVM Values when adding Values to
358/// its work list and inspecting the state of control-flow related values.
359template <> struct LatticeKeyInfo<CVPLatticeKey> {
360 static inline Value *getValueFromLatticeKey(CVPLatticeKey Key) {
361 return Key.getPointer();
362 }
363 static inline CVPLatticeKey getLatticeKeyFromValue(Value *V) {
364 return CVPLatticeKey(V, IPOGrouping::Register);
365 }
366};
367} // namespace llvm
368
369static bool runCVP(Module &M) {
370 // Our custom lattice function and generic sparse propagation solver.
371 CVPLatticeFunc Lattice;
373
374 // For each function in the module, if we can't track its arguments, let the
375 // generic solver assume it is executable.
376 for (Function &F : M)
377 if (!F.isDeclaration() && !canTrackArgumentsInterprocedurally(&F))
378 Solver.MarkBlockExecutable(&F.front());
379
380 // Solver our custom lattice. In doing so, we will also build a set of
381 // indirect call sites.
382 Solver.Solve();
383
384 // Attach metadata to the indirect call sites that were collected indicating
385 // the set of functions they can possibly target.
386 bool Changed = false;
387 MDBuilder MDB(M.getContext());
388 for (CallBase *C : Lattice.getIndirectCalls()) {
389 auto RegI = CVPLatticeKey(C->getCalledOperand(), IPOGrouping::Register);
390 CVPLatticeVal LV = Solver.getExistingValueState(RegI);
391 if (!LV.isFunctionSet() || LV.getFunctions().empty())
392 continue;
393 MDNode *Callees = MDB.createCallees(LV.getFunctions());
394 C->setMetadata(LLVMContext::MD_callees, Callees);
395 Changed = true;
396 }
397
398 return Changed;
399}
400
403 runCVP(M);
404 return PreservedAnalyses::all();
405}
static GCRegistry::Add< ErlangGC > A("erlang", "erlang-compatible garbage collector")
static cl::opt< unsigned > MaxFunctionsPerValue("cvp-max-functions-per-value", cl::Hidden, cl::init(4), cl::desc("The maximum number of functions to track per lattice value"))
The maximum number of functions to track per lattice value.
static bool runCVP(Module &M)
This file contains the declarations for the subclasses of Constant, which represent the different fla...
static GCMetadataPrinterRegistry::Add< ErlangGCPrinter > X("erlang", "erlang-compatible garbage collector")
#define F(x, y, z)
Definition: MD5.cpp:55
#define I(x, y, z)
Definition: MD5.cpp:58
static GCMetadataPrinterRegistry::Add< OcamlGCMetadataPrinter > Y("ocaml", "ocaml 3.10-compatible collector")
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
raw_pwrite_stream & OS
Value * RHS
Value * LHS
AbstractLatticeFunction - This class is implemented by the dataflow instance to specify what the latt...
LatticeVal getOverdefinedVal() const
virtual void ComputeInstructionState(Instruction &I, DenseMap< LatticeKey, LatticeVal > &ChangedValues, SparseSolver< LatticeKey, LatticeVal > &SS)=0
ComputeInstructionState - Compute the LatticeKeys that change as a result of executing instruction I.
virtual void PrintLatticeKey(LatticeKey Key, raw_ostream &OS)
PrintLatticeKey - Render the given LatticeKey to the specified stream.
virtual void PrintLatticeVal(LatticeVal LV, raw_ostream &OS)
PrintLatticeVal - Render the given LatticeVal to the specified stream.
LatticeVal getUntrackedVal() const
virtual LatticeVal MergeValues(LatticeVal X, LatticeVal Y)
MergeValues - Compute and return the merge of the two specified lattice values.
virtual LatticeVal ComputeLatticeVal(LatticeKey Key)
ComputeLatticeVal - Compute and return a LatticeVal corresponding to the given LatticeKey.
A container for analyses that lazily runs them and caches their results.
Definition: PassManager.h:321
This class represents an incoming formal argument to a Function.
Definition: Argument.h:31
Base class for all callable instructions (InvokeInst and CallInst) Holds everything related to callin...
Definition: InstrTypes.h:1467
Function * getCalledFunction() const
Returns the function called, or null if this is an indirect function invocation or the function signa...
Definition: InstrTypes.h:1715
Value * getArgOperand(unsigned i) const
Definition: InstrTypes.h:1660
PreservedAnalyses run(Module &M, ModuleAnalysisManager &)
This is an important base class in LLVM.
Definition: Constant.h:41
An instruction for reading from memory.
Definition: Instructions.h:184
MDNode * createCallees(ArrayRef< Function * > Callees)
Return metadata indicating the possible callees of indirect calls.
Definition: MDBuilder.cpp:100
Metadata node.
Definition: Metadata.h:1067
A Module instance is used to store all the information related to an LLVM module.
Definition: Module.h:65
PointerIntPair - This class implements a pair of a pointer and small integer.
A set of analyses that are preserved following a run of a transformation pass.
Definition: Analysis.h:109
static PreservedAnalyses all()
Construct a special preserved set that preserves all passes.
Definition: Analysis.h:115
Wrapper class representing virtual and physical registers.
Definition: Register.h:19
Return a value (possibly void), from a function.
This class represents the LLVM 'select' instruction.
A templated base class for SmallPtrSet which provides the typesafe interface that is common across al...
Definition: SmallPtrSet.h:321
std::pair< iterator, bool > insert(PtrType Ptr)
Inserts Ptr if and only if there is no element in the container equal to Ptr.
Definition: SmallPtrSet.h:342
SmallPtrSet - This class implements a set which is optimized for holding SmallSize or less elements.
Definition: SmallPtrSet.h:427
SparseSolver - This class is a general purpose solver for Sparse Conditional Propagation with a progr...
void MarkBlockExecutable(BasicBlock *BB)
MarkBlockExecutable - This method can be used by clients to mark all of the blocks that are known to ...
void Solve()
Solve - Solve for constants and executable blocks.
LatticeVal getExistingValueState(LatticeKey Key) const
getExistingValueState - Return the LatticeVal object corresponding to the given value from the ValueS...
An instruction for storing to memory.
Definition: Instructions.h:317
bool isVoidTy() const
Return true if this is 'void'.
Definition: Type.h:140
LLVM Value Representation.
Definition: Value.h:74
Type * getType() const
All values are typed, get the type of this value.
Definition: Value.h:255
StringRef getName() const
Return a constant reference to the value's name.
Definition: Value.cpp:309
This class implements an extremely fast bulk output stream that can only output to a stream.
Definition: raw_ostream.h:52
This class provides various memory handling functions that manipulate MemoryBlock instances.
Definition: Memory.h:52
Key
PAL metadata keys.
@ C
The default llvm calling convention, compatible with C.
Definition: CallingConv.h:34
@ SS
Definition: X86.h:207
initializer< Ty > init(const Ty &Val)
Definition: CommandLine.h:450
This is an optimization pass for GlobalISel generic memory operations.
Definition: AddressRanges.h:18
bool operator!=(uint64_t V1, const APInt &V2)
Definition: APInt.h:2043
bool operator==(const AddressRangeValuePair &LHS, const AddressRangeValuePair &RHS)
bool canTrackGlobalVariableInterprocedurally(GlobalVariable *GV)
Determine if the value maintained in the given global variable can be tracked interprocedurally.
bool is_sorted(R &&Range, Compare C)
Wrapper function around std::is_sorted to check if elements in a range R are sorted with respect to a...
Definition: STLExtras.h:1902
bool canTrackReturnsInterprocedurally(Function *F)
Determine if the values of the given function's returns can be tracked interprocedurally.
OutputIt move(R &&Range, OutputIt Out)
Provide wrappers to std::move which take ranges instead of having to pass begin/end explicitly.
Definition: STLExtras.h:1849
bool canTrackArgumentsInterprocedurally(Function *F)
Determine if the values of the given function's arguments can be tracked interprocedurally.
Implement std::hash so that hash_code can be used in STL containers.
Definition: BitVector.h:858
static CVPLatticeKey getLatticeKeyFromValue(Value *V)
static Value * getValueFromLatticeKey(CVPLatticeKey Key)
A template for translating between LLVM Values and LatticeKeys.