1//===- PGOCtxProfLowering.cpp - Contextual PGO Instr. Lowering ------------===//
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
10#include "llvm/Transforms/Instrumentation/PGOCtxProfLowering.h"
11#include "llvm/ADT/STLExtras.h"
12#include "llvm/Analysis/CFG.h"
13#include "llvm/Analysis/CtxProfAnalysis.h"
14#include "llvm/Analysis/OptimizationRemarkEmitter.h"
15#include "llvm/IR/Analysis.h"
16#include "llvm/IR/Constants.h"
17#include "llvm/IR/DiagnosticInfo.h"
18#include "llvm/IR/GlobalValue.h"
19#include "llvm/IR/IRBuilder.h"
20#include "llvm/IR/InstrTypes.h"
21#include "llvm/IR/Instructions.h"
22#include "llvm/IR/IntrinsicInst.h"
23#include "llvm/IR/Module.h"
24#include "llvm/IR/PassManager.h"
25#include "llvm/ProfileData/CtxInstrContextNode.h"
26#include "llvm/ProfileData/InstrProf.h"
27#include "llvm/Support/CommandLine.h"
28#include <utility>
29
30using namespace llvm;
31
32#define DEBUG_TYPE "ctx-instr-lower"
33
34static cl::list<std::string> ContextRoots(
35 "profile-context-root", cl::Hidden,
36 cl::desc(
37 "A function name, assumed to be global, which will be treated as the "
38 "root of an interesting graph, which will be profiled independently "
39 "from other similar graphs."));
40
41bool PGOCtxProfLoweringPass::isCtxIRPGOInstrEnabled() {
42 return !ContextRoots.empty();
43}
44
45// the names of symbols we expect in compiler-rt. Using a namespace for
46// readability.
47namespace CompilerRtAPINames {
48static auto StartCtx = "__llvm_ctx_profile_start_context";
49static auto ReleaseCtx = "__llvm_ctx_profile_release_context";
50static auto GetCtx = "__llvm_ctx_profile_get_context";
51static auto ExpectedCalleeTLS = "__llvm_ctx_profile_expected_callee";
52static auto CallsiteTLS = "__llvm_ctx_profile_callsite";
53} // namespace CompilerRtAPINames
54
55namespace {
56// The lowering logic and state.
57class CtxInstrumentationLowerer final {
58 Module &M;
59 ModuleAnalysisManager &MAM;
60 Type *ContextNodeTy = nullptr;
61 StructType *FunctionDataTy = nullptr;
62
63 DenseSet<const Function *> ContextRootSet;
64 Function *StartCtx = nullptr;
65 Function *GetCtx = nullptr;
66 Function *ReleaseCtx = nullptr;
67 GlobalVariable *ExpectedCalleeTLS = nullptr;
68 GlobalVariable *CallsiteInfoTLS = nullptr;
69 Constant *CannotBeRootInitializer = nullptr;
70
71public:
72 CtxInstrumentationLowerer(Module &M, ModuleAnalysisManager &MAM);
73 // return true if lowering happened (i.e. a change was made)
74 bool lowerFunction(Function &F);
75};
76
77// llvm.instrprof.increment[.step] captures the total number of counters as one
78// of its parameters, and llvm.instrprof.callsite captures the total number of
79// callsites. Those values are the same for instances of those intrinsics in
80// this function. Find the first instance of each and return them.
81std::pair<uint32_t, uint32_t> getNumCountersAndCallsites(const Function &F) {
82 uint32_t NumCounters = 0;
83 uint32_t NumCallsites = 0;
84 for (const auto &BB : F) {
85 for (const auto &I : BB) {
86 if (const auto *Incr = dyn_cast<InstrProfIncrementInst>(Val: &I)) {
87 uint32_t V =
88 static_cast<uint32_t>(Incr->getNumCounters()->getZExtValue());
89 assert((!NumCounters || V == NumCounters) &&
90 "expected all llvm.instrprof.increment[.step] intrinsics to "
91 "have the same total nr of counters parameter");
92 NumCounters = V;
93 } else if (const auto *CSIntr = dyn_cast<InstrProfCallsite>(Val: &I)) {
94 uint32_t V =
95 static_cast<uint32_t>(CSIntr->getNumCounters()->getZExtValue());
96 assert((!NumCallsites || V == NumCallsites) &&
97 "expected all llvm.instrprof.callsite intrinsics to have the "
98 "same total nr of callsites parameter");
99 NumCallsites = V;
100 }
101#ifdef NDEBUG
102 if (NumCounters && NumCallsites)
103 return std::make_pair(x&: NumCounters, y&: NumCallsites);
104#endif
105 }
106 }
107 return {NumCounters, NumCallsites};
108}
109
110void emitUnsupportedRootError(const Function &F, StringRef Reason) {
111 F.getContext().emitError(ErrorStr: "[ctxprof] The function " + F.getName() +
112 " was indicated as context root but " + Reason +
113 ", which is not supported.");
114}
115} // namespace
116
117// set up tie-in with compiler-rt.
118// NOTE!!!
119// These have to match compiler-rt/lib/ctx_profile/CtxInstrProfiling.h
120CtxInstrumentationLowerer::CtxInstrumentationLowerer(Module &M,
121 ModuleAnalysisManager &MAM)
122 : M(M), MAM(MAM) {
123 auto *PointerTy = PointerType::get(C&: M.getContext(), AddressSpace: 0);
124 auto *SanitizerMutexType = Type::getInt8Ty(C&: M.getContext());
125 auto *I32Ty = Type::getInt32Ty(C&: M.getContext());
126 auto *I64Ty = Type::getInt64Ty(C&: M.getContext());
127
128#define _PTRDECL(_, __) PointerTy,
129#define _VOLATILE_PTRDECL(_, __) PointerTy,
130#define _CONTEXT_ROOT PointerTy,
131#define _MUTEXDECL(_) SanitizerMutexType,
132
133 FunctionDataTy = StructType::get(
134 Context&: M.getContext(), Elements: {CTXPROF_FUNCTION_DATA(_PTRDECL, _CONTEXT_ROOT,
135 _VOLATILE_PTRDECL, _MUTEXDECL)});
136#undef _PTRDECL
137#undef _CONTEXT_ROOT
138#undef _VOLATILE_PTRDECL
139#undef _MUTEXDECL
140
141#define _PTRDECL(_, __) Constant::getNullValue(PointerTy),
142#define _VOLATILE_PTRDECL(_, __) _PTRDECL(_, __)
143#define _MUTEXDECL(_) Constant::getNullValue(SanitizerMutexType),
144#define _CONTEXT_ROOT \
145 Constant::getIntegerValue( \
146 PointerTy, \
147 APInt(M.getDataLayout().getPointerTypeSizeInBits(PointerTy), 1U)),
148 CannotBeRootInitializer = ConstantStruct::get(
149 T: FunctionDataTy, V: {CTXPROF_FUNCTION_DATA(_PTRDECL, _CONTEXT_ROOT,
150 _VOLATILE_PTRDECL, _MUTEXDECL)});
151#undef _PTRDECL
152#undef _CONTEXT_ROOT
153#undef _VOLATILE_PTRDECL
154#undef _MUTEXDECL
155
156 // The Context header.
157 ContextNodeTy = StructType::get(Context&: M.getContext(), Elements: {
158 I64Ty, /*Guid*/
159 PointerTy, /*Next*/
160 I32Ty, /*NumCounters*/
161 I32Ty, /*NumCallsites*/
162 });
163
164 // Define a global for each entrypoint. We'll reuse the entrypoint's name
165 // as prefix. We assume the entrypoint names to be unique.
166 for (const auto &Fname : ContextRoots) {
167 if (const auto *F = M.getFunction(Name: Fname)) {
168 if (F->isDeclaration())
169 continue;
170 ContextRootSet.insert(V: F);
171 for (const auto &BB : *F)
172 for (const auto &I : BB)
173 if (const auto *CB = dyn_cast<CallBase>(Val: &I))
174 if (CB->isMustTailCall())
175 emitUnsupportedRootError(F: *F, Reason: "it features musttail calls");
176 }
177 }
178
179 // Declare the functions we will call.
180 StartCtx = cast<Function>(
181 Val: M.getOrInsertFunction(
182 Name: CompilerRtAPINames::StartCtx,
183 T: FunctionType::get(Result: PointerTy,
184 Params: {PointerTy, /*FunctionData*/
185 I64Ty, /*Guid*/ I32Ty,
186 /*NumCounters*/ I32Ty /*NumCallsites*/},
187 isVarArg: false))
188 .getCallee());
189 GetCtx = cast<Function>(
190 Val: M.getOrInsertFunction(Name: CompilerRtAPINames::GetCtx,
191 T: FunctionType::get(Result: PointerTy,
192 Params: {PointerTy, /*FunctionData*/
193 PointerTy, /*Callee*/
194 I64Ty, /*Guid*/
195 I32Ty, /*NumCounters*/
196 I32Ty}, /*NumCallsites*/
197 isVarArg: false))
198 .getCallee());
199 ReleaseCtx = cast<Function>(
200 Val: M.getOrInsertFunction(Name: CompilerRtAPINames::ReleaseCtx,
201 T: FunctionType::get(Result: Type::getVoidTy(C&: M.getContext()),
202 Params: {
203 PointerTy, /*FunctionData*/
204 },
205 isVarArg: false))
206 .getCallee());
207
208 // Declare the TLSes we will need to use.
209 CallsiteInfoTLS =
210 new GlobalVariable(M, PointerTy, false, GlobalValue::ExternalLinkage,
211 nullptr, CompilerRtAPINames::CallsiteTLS);
212 CallsiteInfoTLS->setThreadLocal(true);
213 CallsiteInfoTLS->setVisibility(llvm::GlobalValue::HiddenVisibility);
214 ExpectedCalleeTLS =
215 new GlobalVariable(M, PointerTy, false, GlobalValue::ExternalLinkage,
216 nullptr, CompilerRtAPINames::ExpectedCalleeTLS);
217 ExpectedCalleeTLS->setThreadLocal(true);
218 ExpectedCalleeTLS->setVisibility(llvm::GlobalValue::HiddenVisibility);
219}
220
221PreservedAnalyses PGOCtxProfLoweringPass::run(Module &M,
222 ModuleAnalysisManager &MAM) {
223 CtxInstrumentationLowerer Lowerer(M, MAM);
224 bool Changed = false;
225 for (auto &F : M)
226 Changed |= Lowerer.lowerFunction(F);
227 return Changed ? PreservedAnalyses::none() : PreservedAnalyses::all();
228}
229
230bool CtxInstrumentationLowerer::lowerFunction(Function &F) {
231 if (F.isDeclaration())
232 return false;
233
234 // Probably pointless to try to do anything here, unlikely to be
235 // performance-affecting.
236 if (!llvm::canReturn(F)) {
237 for (auto &BB : F)
238 for (auto &I : make_early_inc_range(Range&: BB))
239 if (isa<InstrProfCntrInstBase>(Val: &I))
240 I.eraseFromParent();
241 if (ContextRootSet.contains(V: &F))
242 emitUnsupportedRootError(F, Reason: "it does not return");
243 return true;
244 }
245
246 auto &FAM = MAM.getResult<FunctionAnalysisManagerModuleProxy>(IR&: M).getManager();
247 auto &ORE = FAM.getResult<OptimizationRemarkEmitterAnalysis>(IR&: F);
248
249 Value *Guid = nullptr;
250 auto [NumCounters, NumCallsites] = getNumCountersAndCallsites(F);
251
252 Value *Context = nullptr;
253 Value *RealContext = nullptr;
254
255 StructType *ThisContextType = nullptr;
256 Value *TheRootFunctionData = nullptr;
257 Value *ExpectedCalleeTLSAddr = nullptr;
258 Value *CallsiteInfoTLSAddr = nullptr;
259 const bool HasMusttail = [&F]() {
260 for (auto &BB : F)
261 for (auto &I : BB)
262 if (auto *CB = dyn_cast<CallBase>(Val: &I))
263 if (CB->isMustTailCall())
264 return true;
265 return false;
266 }();
267
268 if (HasMusttail && ContextRootSet.contains(V: &F)) {
269 F.getContext().emitError(
270 ErrorStr: "[ctx_prof] A function with musttail calls was explicitly requested as "
271 "root. That is not supported because we cannot instrument a return "
272 "instruction to release the context: " +
273 F.getName());
274 return false;
275 }
276 auto &Head = F.getEntryBlock();
277 for (auto &I : Head) {
278 // Find the increment intrinsic in the entry basic block.
279 if (auto *Mark = dyn_cast<InstrProfIncrementInst>(Val: &I)) {
280 assert(Mark->getIndex()->isZero());
281
282 IRBuilder<> Builder(Mark);
283 Guid = Builder.getInt64(
284 C: AssignGUIDPass::getGUID(F: cast<Function>(Val&: *Mark->getNameValue())));
285 // The type of the context of this function is now knowable since we have
286 // NumCallsites and NumCounters. We declare it here because it's more
287 // convenient - we have the Builder.
288 ThisContextType = StructType::get(
289 Context&: F.getContext(),
290 Elements: {ContextNodeTy, ArrayType::get(ElementType: Builder.getInt64Ty(), NumElements: NumCounters),
291 ArrayType::get(ElementType: Builder.getPtrTy(), NumElements: NumCallsites)});
292 // Figure out which way we obtain the context object for this function -
293 // if it's an entrypoint, then we call StartCtx, otherwise GetCtx. In the
294 // former case, we also set TheRootFunctionData since we need to release
295 // it at the end (plus it can be used to know if we have an entrypoint or
296 // a regular function). Don't set a name, they end up taking a lot of
297 // space and we don't need them.
298
299 // Zero-initialize the FunctionData, except for functions that have
300 // musttail calls. There, we set the CtxRoot field to 1, which will be
301 // treated as a "can't be set as root".
302 TheRootFunctionData = new GlobalVariable(
303 M, FunctionDataTy, false, GlobalVariable::InternalLinkage,
304 HasMusttail ? CannotBeRootInitializer
305 : Constant::getNullValue(Ty: FunctionDataTy));
306
307 if (ContextRootSet.contains(V: &F)) {
308 Context = Builder.CreateCall(
309 Callee: StartCtx, Args: {TheRootFunctionData, Guid, Builder.getInt32(C: NumCounters),
310 Builder.getInt32(C: NumCallsites)});
311 ORE.emit(
312 RemarkBuilder: [&] { return OptimizationRemark(DEBUG_TYPE, "Entrypoint", &F); });
313 } else {
314 Context = Builder.CreateCall(Callee: GetCtx, Args: {TheRootFunctionData, &F, Guid,
315 Builder.getInt32(C: NumCounters),
316 Builder.getInt32(C: NumCallsites)});
317 ORE.emit(RemarkBuilder: [&] {
318 return OptimizationRemark(DEBUG_TYPE, "RegularFunction", &F);
319 });
320 }
321 // The context could be scratch.
322 auto *CtxAsInt = Builder.CreatePtrToInt(V: Context, DestTy: Builder.getInt64Ty());
323 if (NumCallsites > 0) {
324 // Figure out which index of the TLS 2-element buffers to use.
325 // Scratch context => we use index == 1. Real contexts => index == 0.
326 auto *Index = Builder.CreateAnd(LHS: CtxAsInt, RHS: Builder.getInt64(C: 1));
327 // The GEPs corresponding to that index, in the respective TLS.
328 ExpectedCalleeTLSAddr = Builder.CreateGEP(
329 Ty: PointerType::getUnqual(C&: F.getContext()),
330 Ptr: Builder.CreateThreadLocalAddress(Ptr: ExpectedCalleeTLS), IdxList: {Index});
331 CallsiteInfoTLSAddr = Builder.CreateGEP(
332 Ty: Builder.getInt32Ty(),
333 Ptr: Builder.CreateThreadLocalAddress(Ptr: CallsiteInfoTLS), IdxList: {Index});
334 }
335 // Because the context pointer may have LSB set (to indicate scratch),
336 // clear it for the value we use as base address for the counter vector.
337 // This way, if later we want to have "real" (not clobbered) buffers
338 // acting as scratch, the lowering (at least this part of it that deals
339 // with counters) stays the same.
340 RealContext = Builder.CreateIntToPtr(
341 V: Builder.CreateAnd(LHS: CtxAsInt, RHS: Builder.getInt64(C: -2)),
342 DestTy: PointerType::getUnqual(C&: F.getContext()));
343 I.eraseFromParent();
344 break;
345 }
346 }
347 if (!Context) {
348 ORE.emit(RemarkBuilder: [&] {
349 return OptimizationRemarkMissed(DEBUG_TYPE, "Skip", &F)
350 << "Function doesn't have instrumentation, skipping";
351 });
352 return false;
353 }
354
355 bool ContextWasReleased = false;
356 for (auto &BB : F) {
357 for (auto &I : llvm::make_early_inc_range(Range&: BB)) {
358 if (auto *Instr = dyn_cast<InstrProfCntrInstBase>(Val: &I)) {
359 IRBuilder<> Builder(Instr);
360 switch (Instr->getIntrinsicID()) {
361 case llvm::Intrinsic::instrprof_increment:
362 case llvm::Intrinsic::instrprof_increment_step: {
363 // Increments (or increment-steps) are just a typical load - increment
364 // - store in the RealContext.
365 auto *AsStep = cast<InstrProfIncrementInst>(Val: Instr);
366 auto *GEP = Builder.CreateGEP(
367 Ty: ThisContextType, Ptr: RealContext,
368 IdxList: {Builder.getInt32(C: 0), Builder.getInt32(C: 1), AsStep->getIndex()});
369 Builder.CreateStore(
370 Val: Builder.CreateAdd(LHS: Builder.CreateLoad(Ty: Builder.getInt64Ty(), Ptr: GEP),
371 RHS: AsStep->getStep()),
372 Ptr: GEP);
373 } break;
374 case llvm::Intrinsic::instrprof_callsite:
375 // callsite lowering: write the called value in the expected callee
376 // TLS we treat the TLS as volatile because of signal handlers and to
377 // avoid these being moved away from the callsite they decorate.
378 auto *CSIntrinsic = dyn_cast<InstrProfCallsite>(Val: Instr);
379 Builder.CreateStore(Val: CSIntrinsic->getCallee(), Ptr: ExpectedCalleeTLSAddr,
380 isVolatile: true);
381 // write the GEP of the slot in the sub-contexts portion of the
382 // context in TLS. Now, here, we use the actual Context value - as
383 // returned from compiler-rt - which may have the LSB set if the
384 // Context was scratch. Since the header of the context object and
385 // then the values are all 8-aligned (or, really, insofar as we care,
386 // they are even) - if the context is scratch (meaning, an odd value),
387 // so will the GEP. This is important because this is then visible to
388 // compiler-rt which will produce scratch contexts for callers that
389 // have a scratch context.
390 Builder.CreateStore(
391 Val: Builder.CreateGEP(Ty: ThisContextType, Ptr: Context,
392 IdxList: {Builder.getInt32(C: 0), Builder.getInt32(C: 2),
393 CSIntrinsic->getIndex()}),
394 Ptr: CallsiteInfoTLSAddr, isVolatile: true);
395 break;
396 }
397 I.eraseFromParent();
398 } else if (!HasMusttail && isa<ReturnInst>(Val: I)) {
399 // Remember to release the context if we are an entrypoint.
400 IRBuilder<> Builder(&I);
401 Builder.CreateCall(Callee: ReleaseCtx, Args: {TheRootFunctionData});
402 ContextWasReleased = true;
403 }
404 }
405 }
406 if (!HasMusttail && !ContextWasReleased)
407 F.getContext().emitError(
408 ErrorStr: "[ctx_prof] A function that doesn't have musttail calls was "
409 "instrumented but it has no `ret` "
410 "instructions above which to release the context: " +
411 F.getName());
412 return true;
413}
414
415PreservedAnalyses NoinlineNonPrevailing::run(Module &M,
416 ModuleAnalysisManager &MAM) {
417 bool Changed = false;
418 for (auto &F : M) {
419 if (F.isDeclaration())
420 continue;
421 if (F.hasFnAttribute(Kind: Attribute::NoInline))
422 continue;
423 if (!F.isWeakForLinker())
424 continue;
425
426 if (F.hasFnAttribute(Kind: Attribute::AlwaysInline))
427 F.removeFnAttr(Kind: Attribute::AlwaysInline);
428
429 F.addFnAttr(Kind: Attribute::NoInline);
430 Changed = true;
431 }
432 if (Changed)
433 return PreservedAnalyses::none();
434 return PreservedAnalyses::all();
435}
436