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
30 using namespace llvm;
31
32 #define DEBUG_TYPE "ctx-instr-lower"
33
34 static 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
isCtxIRPGOInstrEnabled()41 bool PGOCtxProfLoweringPass::isCtxIRPGOInstrEnabled() {
42 return !ContextRoots.empty();
43 }
44
45 // the names of symbols we expect in compiler-rt. Using a namespace for
46 // readability.
47 namespace CompilerRtAPINames {
48 static auto StartCtx = "__llvm_ctx_profile_start_context";
49 static auto ReleaseCtx = "__llvm_ctx_profile_release_context";
50 static auto GetCtx = "__llvm_ctx_profile_get_context";
51 static auto ExpectedCalleeTLS = "__llvm_ctx_profile_expected_callee";
52 static auto CallsiteTLS = "__llvm_ctx_profile_callsite";
53 } // namespace CompilerRtAPINames
54
55 namespace {
56 // The lowering logic and state.
57 class 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
71 public:
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.
getNumCountersAndCallsites(const Function & F)81 std::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>(&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>(&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 #if NDEBUG
102 if (NumCounters && NumCallsites)
103 return std::make_pair(NumCounters, NumCallsites);
104 #endif
105 }
106 }
107 return {NumCounters, NumCallsites};
108 }
109
emitUnsupportedRootError(const Function & F,StringRef Reason)110 void emitUnsupportedRootError(const Function &F, StringRef Reason) {
111 F.getContext().emitError("[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
CtxInstrumentationLowerer(Module & M,ModuleAnalysisManager & MAM)120 CtxInstrumentationLowerer::CtxInstrumentationLowerer(Module &M,
121 ModuleAnalysisManager &MAM)
122 : M(M), MAM(MAM) {
123 auto *PointerTy = PointerType::get(M.getContext(), 0);
124 auto *SanitizerMutexType = Type::getInt8Ty(M.getContext());
125 auto *I32Ty = Type::getInt32Ty(M.getContext());
126 auto *I64Ty = Type::getInt64Ty(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 M.getContext(), {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 FunctionDataTy, {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(M.getContext(), {
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(Fname)) {
168 if (F->isDeclaration())
169 continue;
170 ContextRootSet.insert(F);
171 for (const auto &BB : *F)
172 for (const auto &I : BB)
173 if (const auto *CB = dyn_cast<CallBase>(&I))
174 if (CB->isMustTailCall())
175 emitUnsupportedRootError(*F, "it features musttail calls");
176 }
177 }
178
179 // Declare the functions we will call.
180 StartCtx = cast<Function>(
181 M.getOrInsertFunction(
182 CompilerRtAPINames::StartCtx,
183 FunctionType::get(PointerTy,
184 {PointerTy, /*FunctionData*/
185 I64Ty, /*Guid*/ I32Ty,
186 /*NumCounters*/ I32Ty /*NumCallsites*/},
187 false))
188 .getCallee());
189 GetCtx = cast<Function>(
190 M.getOrInsertFunction(CompilerRtAPINames::GetCtx,
191 FunctionType::get(PointerTy,
192 {PointerTy, /*FunctionData*/
193 PointerTy, /*Callee*/
194 I64Ty, /*Guid*/
195 I32Ty, /*NumCounters*/
196 I32Ty}, /*NumCallsites*/
197 false))
198 .getCallee());
199 ReleaseCtx = cast<Function>(
200 M.getOrInsertFunction(CompilerRtAPINames::ReleaseCtx,
201 FunctionType::get(Type::getVoidTy(M.getContext()),
202 {
203 PointerTy, /*FunctionData*/
204 },
205 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
run(Module & M,ModuleAnalysisManager & MAM)221 PreservedAnalyses 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
lowerFunction(Function & F)230 bool 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(BB))
239 if (isa<InstrProfCntrInstBase>(&I))
240 I.eraseFromParent();
241 if (ContextRootSet.contains(&F))
242 emitUnsupportedRootError(F, "it does not return");
243 return true;
244 }
245
246 auto &FAM = MAM.getResult<FunctionAnalysisManagerModuleProxy>(M).getManager();
247 auto &ORE = FAM.getResult<OptimizationRemarkEmitterAnalysis>(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 *TheRootFuctionData = 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>(&I))
263 if (CB->isMustTailCall())
264 return true;
265 return false;
266 }();
267
268 if (HasMusttail && ContextRootSet.contains(&F)) {
269 F.getContext().emitError(
270 "[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>(&I)) {
280 assert(Mark->getIndex()->isZero());
281
282 IRBuilder<> Builder(Mark);
283 Guid = Builder.getInt64(
284 AssignGUIDPass::getGUID(cast<Function>(*Mark->getNameValue())));
285 // The type of the context of this function is now knowable since we have
286 // NumCallsites and NumCounters. We delcare it here because it's more
287 // convenient - we have the Builder.
288 ThisContextType = StructType::get(
289 F.getContext(),
290 {ContextNodeTy, ArrayType::get(Builder.getInt64Ty(), NumCounters),
291 ArrayType::get(Builder.getPtrTy(), 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 TheRootFuctionData since we need to release it
295 // at the end (plus it can be used to know if we have an entrypoint or a
296 // regular function)
297 // Don't set a name, they end up taking a lot of space and we don't need
298 // them.
299
300 // Zero-initialize the FunctionData, except for functions that have
301 // musttail calls. There, we set the CtxRoot field to 1, which will be
302 // treated as a "can't be set as root".
303 TheRootFuctionData = new GlobalVariable(
304 M, FunctionDataTy, false, GlobalVariable::InternalLinkage,
305 HasMusttail ? CannotBeRootInitializer
306 : Constant::getNullValue(FunctionDataTy));
307
308 if (ContextRootSet.contains(&F)) {
309 Context = Builder.CreateCall(
310 StartCtx, {TheRootFuctionData, Guid, Builder.getInt32(NumCounters),
311 Builder.getInt32(NumCallsites)});
312 ORE.emit(
313 [&] { return OptimizationRemark(DEBUG_TYPE, "Entrypoint", &F); });
314 } else {
315 Context = Builder.CreateCall(GetCtx, {TheRootFuctionData, &F, Guid,
316 Builder.getInt32(NumCounters),
317 Builder.getInt32(NumCallsites)});
318 ORE.emit([&] {
319 return OptimizationRemark(DEBUG_TYPE, "RegularFunction", &F);
320 });
321 }
322 // The context could be scratch.
323 auto *CtxAsInt = Builder.CreatePtrToInt(Context, Builder.getInt64Ty());
324 if (NumCallsites > 0) {
325 // Figure out which index of the TLS 2-element buffers to use.
326 // Scratch context => we use index == 1. Real contexts => index == 0.
327 auto *Index = Builder.CreateAnd(CtxAsInt, Builder.getInt64(1));
328 // The GEPs corresponding to that index, in the respective TLS.
329 ExpectedCalleeTLSAddr = Builder.CreateGEP(
330 PointerType::getUnqual(F.getContext()),
331 Builder.CreateThreadLocalAddress(ExpectedCalleeTLS), {Index});
332 CallsiteInfoTLSAddr = Builder.CreateGEP(
333 Builder.getInt32Ty(),
334 Builder.CreateThreadLocalAddress(CallsiteInfoTLS), {Index});
335 }
336 // Because the context pointer may have LSB set (to indicate scratch),
337 // clear it for the value we use as base address for the counter vector.
338 // This way, if later we want to have "real" (not clobbered) buffers
339 // acting as scratch, the lowering (at least this part of it that deals
340 // with counters) stays the same.
341 RealContext = Builder.CreateIntToPtr(
342 Builder.CreateAnd(CtxAsInt, Builder.getInt64(-2)),
343 PointerType::getUnqual(F.getContext()));
344 I.eraseFromParent();
345 break;
346 }
347 }
348 if (!Context) {
349 ORE.emit([&] {
350 return OptimizationRemarkMissed(DEBUG_TYPE, "Skip", &F)
351 << "Function doesn't have instrumentation, skipping";
352 });
353 return false;
354 }
355
356 bool ContextWasReleased = false;
357 for (auto &BB : F) {
358 for (auto &I : llvm::make_early_inc_range(BB)) {
359 if (auto *Instr = dyn_cast<InstrProfCntrInstBase>(&I)) {
360 IRBuilder<> Builder(Instr);
361 switch (Instr->getIntrinsicID()) {
362 case llvm::Intrinsic::instrprof_increment:
363 case llvm::Intrinsic::instrprof_increment_step: {
364 // Increments (or increment-steps) are just a typical load - increment
365 // - store in the RealContext.
366 auto *AsStep = cast<InstrProfIncrementInst>(Instr);
367 auto *GEP = Builder.CreateGEP(
368 ThisContextType, RealContext,
369 {Builder.getInt32(0), Builder.getInt32(1), AsStep->getIndex()});
370 Builder.CreateStore(
371 Builder.CreateAdd(Builder.CreateLoad(Builder.getInt64Ty(), GEP),
372 AsStep->getStep()),
373 GEP);
374 } break;
375 case llvm::Intrinsic::instrprof_callsite:
376 // callsite lowering: write the called value in the expected callee
377 // TLS we treat the TLS as volatile because of signal handlers and to
378 // avoid these being moved away from the callsite they decorate.
379 auto *CSIntrinsic = dyn_cast<InstrProfCallsite>(Instr);
380 Builder.CreateStore(CSIntrinsic->getCallee(), ExpectedCalleeTLSAddr,
381 true);
382 // write the GEP of the slot in the sub-contexts portion of the
383 // context in TLS. Now, here, we use the actual Context value - as
384 // returned from compiler-rt - which may have the LSB set if the
385 // Context was scratch. Since the header of the context object and
386 // then the values are all 8-aligned (or, really, insofar as we care,
387 // they are even) - if the context is scratch (meaning, an odd value),
388 // so will the GEP. This is important because this is then visible to
389 // compiler-rt which will produce scratch contexts for callers that
390 // have a scratch context.
391 Builder.CreateStore(
392 Builder.CreateGEP(ThisContextType, Context,
393 {Builder.getInt32(0), Builder.getInt32(2),
394 CSIntrinsic->getIndex()}),
395 CallsiteInfoTLSAddr, true);
396 break;
397 }
398 I.eraseFromParent();
399 } else if (!HasMusttail && isa<ReturnInst>(I)) {
400 // Remember to release the context if we are an entrypoint.
401 IRBuilder<> Builder(&I);
402 Builder.CreateCall(ReleaseCtx, {TheRootFuctionData});
403 ContextWasReleased = true;
404 }
405 }
406 }
407 if (!HasMusttail && !ContextWasReleased)
408 F.getContext().emitError(
409 "[ctx_prof] A function that doesn't have musttail calls was "
410 "instrumented but it has no `ret` "
411 "instructions above which to release the context: " +
412 F.getName());
413 return true;
414 }
415
run(Module & M,ModuleAnalysisManager & MAM)416 PreservedAnalyses NoinlineNonPrevailing::run(Module &M,
417 ModuleAnalysisManager &MAM) {
418 bool Changed = false;
419 for (auto &F : M) {
420 if (F.isDeclaration())
421 continue;
422 if (F.hasFnAttribute(Attribute::NoInline))
423 continue;
424 if (!F.isWeakForLinker())
425 continue;
426
427 if (F.hasFnAttribute(Attribute::AlwaysInline))
428 F.removeFnAttr(Attribute::AlwaysInline);
429
430 F.addFnAttr(Attribute::NoInline);
431 Changed = true;
432 }
433 if (Changed)
434 return PreservedAnalyses::none();
435 return PreservedAnalyses::all();
436 }
437