blob: d741695d4e53cebc7bb1638e8d7021401a5cadb8 [file] [log] [blame]
//===- PGOCtxProfLowering.cpp - Contextual PGO Instr. Lowering ------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
#include "llvm/Transforms/Instrumentation/PGOCtxProfLowering.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/Analysis/CFG.h"
#include "llvm/Analysis/CtxProfAnalysis.h"
#include "llvm/Analysis/OptimizationRemarkEmitter.h"
#include "llvm/IR/Analysis.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DiagnosticInfo.h"
#include "llvm/IR/GlobalValue.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/InstrTypes.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/PassManager.h"
#include "llvm/ProfileData/CtxInstrContextNode.h"
#include "llvm/ProfileData/InstrProf.h"
#include "llvm/Support/CommandLine.h"
#include <utility>
using namespace llvm;
#define DEBUG_TYPE "ctx-instr-lower"
static cl::list<std::string> ContextRoots(
"profile-context-root", cl::Hidden,
cl::desc(
"A function name, assumed to be global, which will be treated as the "
"root of an interesting graph, which will be profiled independently "
"from other similar graphs."));
bool PGOCtxProfLoweringPass::isCtxIRPGOInstrEnabled() {
return !ContextRoots.empty();
}
// the names of symbols we expect in compiler-rt. Using a namespace for
// readability.
namespace CompilerRtAPINames {
static auto StartCtx = "__llvm_ctx_profile_start_context";
static auto ReleaseCtx = "__llvm_ctx_profile_release_context";
static auto GetCtx = "__llvm_ctx_profile_get_context";
static auto ExpectedCalleeTLS = "__llvm_ctx_profile_expected_callee";
static auto CallsiteTLS = "__llvm_ctx_profile_callsite";
} // namespace CompilerRtAPINames
namespace {
// The lowering logic and state.
class CtxInstrumentationLowerer final {
Module &M;
ModuleAnalysisManager &MAM;
Type *ContextNodeTy = nullptr;
StructType *FunctionDataTy = nullptr;
DenseSet<const Function *> ContextRootSet;
Function *StartCtx = nullptr;
Function *GetCtx = nullptr;
Function *ReleaseCtx = nullptr;
GlobalVariable *ExpectedCalleeTLS = nullptr;
GlobalVariable *CallsiteInfoTLS = nullptr;
Constant *CannotBeRootInitializer = nullptr;
public:
CtxInstrumentationLowerer(Module &M, ModuleAnalysisManager &MAM);
// return true if lowering happened (i.e. a change was made)
bool lowerFunction(Function &F);
};
// llvm.instrprof.increment[.step] captures the total number of counters as one
// of its parameters, and llvm.instrprof.callsite captures the total number of
// callsites. Those values are the same for instances of those intrinsics in
// this function. Find the first instance of each and return them.
std::pair<uint32_t, uint32_t> getNumCountersAndCallsites(const Function &F) {
uint32_t NumCounters = 0;
uint32_t NumCallsites = 0;
for (const auto &BB : F) {
for (const auto &I : BB) {
if (const auto *Incr = dyn_cast<InstrProfIncrementInst>(&I)) {
uint32_t V =
static_cast<uint32_t>(Incr->getNumCounters()->getZExtValue());
assert((!NumCounters || V == NumCounters) &&
"expected all llvm.instrprof.increment[.step] intrinsics to "
"have the same total nr of counters parameter");
NumCounters = V;
} else if (const auto *CSIntr = dyn_cast<InstrProfCallsite>(&I)) {
uint32_t V =
static_cast<uint32_t>(CSIntr->getNumCounters()->getZExtValue());
assert((!NumCallsites || V == NumCallsites) &&
"expected all llvm.instrprof.callsite intrinsics to have the "
"same total nr of callsites parameter");
NumCallsites = V;
}
#if NDEBUG
if (NumCounters && NumCallsites)
return std::make_pair(NumCounters, NumCallsites);
#endif
}
}
return {NumCounters, NumCallsites};
}
void emitUnsupportedRootError(const Function &F, StringRef Reason) {
F.getContext().emitError("[ctxprof] The function " + F.getName() +
" was indicated as context root but " + Reason +
", which is not supported.");
}
} // namespace
// set up tie-in with compiler-rt.
// NOTE!!!
// These have to match compiler-rt/lib/ctx_profile/CtxInstrProfiling.h
CtxInstrumentationLowerer::CtxInstrumentationLowerer(Module &M,
ModuleAnalysisManager &MAM)
: M(M), MAM(MAM) {
auto *PointerTy = PointerType::get(M.getContext(), 0);
auto *SanitizerMutexType = Type::getInt8Ty(M.getContext());
auto *I32Ty = Type::getInt32Ty(M.getContext());
auto *I64Ty = Type::getInt64Ty(M.getContext());
#define _PTRDECL(_, __) PointerTy,
#define _VOLATILE_PTRDECL(_, __) PointerTy,
#define _CONTEXT_ROOT PointerTy,
#define _MUTEXDECL(_) SanitizerMutexType,
FunctionDataTy = StructType::get(
M.getContext(), {CTXPROF_FUNCTION_DATA(_PTRDECL, _CONTEXT_ROOT,
_VOLATILE_PTRDECL, _MUTEXDECL)});
#undef _PTRDECL
#undef _CONTEXT_ROOT
#undef _VOLATILE_PTRDECL
#undef _MUTEXDECL
#define _PTRDECL(_, __) Constant::getNullValue(PointerTy),
#define _VOLATILE_PTRDECL(_, __) _PTRDECL(_, __)
#define _MUTEXDECL(_) Constant::getNullValue(SanitizerMutexType),
#define _CONTEXT_ROOT \
Constant::getIntegerValue( \
PointerTy, \
APInt(M.getDataLayout().getPointerTypeSizeInBits(PointerTy), 1U)),
CannotBeRootInitializer = ConstantStruct::get(
FunctionDataTy, {CTXPROF_FUNCTION_DATA(_PTRDECL, _CONTEXT_ROOT,
_VOLATILE_PTRDECL, _MUTEXDECL)});
#undef _PTRDECL
#undef _CONTEXT_ROOT
#undef _VOLATILE_PTRDECL
#undef _MUTEXDECL
// The Context header.
ContextNodeTy = StructType::get(M.getContext(), {
I64Ty, /*Guid*/
PointerTy, /*Next*/
I32Ty, /*NumCounters*/
I32Ty, /*NumCallsites*/
});
// Define a global for each entrypoint. We'll reuse the entrypoint's name
// as prefix. We assume the entrypoint names to be unique.
for (const auto &Fname : ContextRoots) {
if (const auto *F = M.getFunction(Fname)) {
if (F->isDeclaration())
continue;
ContextRootSet.insert(F);
for (const auto &BB : *F)
for (const auto &I : BB)
if (const auto *CB = dyn_cast<CallBase>(&I))
if (CB->isMustTailCall())
emitUnsupportedRootError(*F, "it features musttail calls");
}
}
// Declare the functions we will call.
StartCtx = cast<Function>(
M.getOrInsertFunction(
CompilerRtAPINames::StartCtx,
FunctionType::get(PointerTy,
{PointerTy, /*FunctionData*/
I64Ty, /*Guid*/ I32Ty,
/*NumCounters*/ I32Ty /*NumCallsites*/},
false))
.getCallee());
GetCtx = cast<Function>(
M.getOrInsertFunction(CompilerRtAPINames::GetCtx,
FunctionType::get(PointerTy,
{PointerTy, /*FunctionData*/
PointerTy, /*Callee*/
I64Ty, /*Guid*/
I32Ty, /*NumCounters*/
I32Ty}, /*NumCallsites*/
false))
.getCallee());
ReleaseCtx = cast<Function>(
M.getOrInsertFunction(CompilerRtAPINames::ReleaseCtx,
FunctionType::get(Type::getVoidTy(M.getContext()),
{
PointerTy, /*FunctionData*/
},
false))
.getCallee());
// Declare the TLSes we will need to use.
CallsiteInfoTLS =
new GlobalVariable(M, PointerTy, false, GlobalValue::ExternalLinkage,
nullptr, CompilerRtAPINames::CallsiteTLS);
CallsiteInfoTLS->setThreadLocal(true);
CallsiteInfoTLS->setVisibility(llvm::GlobalValue::HiddenVisibility);
ExpectedCalleeTLS =
new GlobalVariable(M, PointerTy, false, GlobalValue::ExternalLinkage,
nullptr, CompilerRtAPINames::ExpectedCalleeTLS);
ExpectedCalleeTLS->setThreadLocal(true);
ExpectedCalleeTLS->setVisibility(llvm::GlobalValue::HiddenVisibility);
}
PreservedAnalyses PGOCtxProfLoweringPass::run(Module &M,
ModuleAnalysisManager &MAM) {
CtxInstrumentationLowerer Lowerer(M, MAM);
bool Changed = false;
for (auto &F : M)
Changed |= Lowerer.lowerFunction(F);
return Changed ? PreservedAnalyses::none() : PreservedAnalyses::all();
}
bool CtxInstrumentationLowerer::lowerFunction(Function &F) {
if (F.isDeclaration())
return false;
// Probably pointless to try to do anything here, unlikely to be
// performance-affecting.
if (!llvm::canReturn(F)) {
for (auto &BB : F)
for (auto &I : make_early_inc_range(BB))
if (isa<InstrProfCntrInstBase>(&I))
I.eraseFromParent();
if (ContextRootSet.contains(&F))
emitUnsupportedRootError(F, "it does not return");
return true;
}
auto &FAM = MAM.getResult<FunctionAnalysisManagerModuleProxy>(M).getManager();
auto &ORE = FAM.getResult<OptimizationRemarkEmitterAnalysis>(F);
Value *Guid = nullptr;
auto [NumCounters, NumCallsites] = getNumCountersAndCallsites(F);
Value *Context = nullptr;
Value *RealContext = nullptr;
StructType *ThisContextType = nullptr;
Value *TheRootFuctionData = nullptr;
Value *ExpectedCalleeTLSAddr = nullptr;
Value *CallsiteInfoTLSAddr = nullptr;
const bool HasMusttail = [&F]() {
for (auto &BB : F)
for (auto &I : BB)
if (auto *CB = dyn_cast<CallBase>(&I))
if (CB->isMustTailCall())
return true;
return false;
}();
if (HasMusttail && ContextRootSet.contains(&F)) {
F.getContext().emitError(
"[ctx_prof] A function with musttail calls was explicitly requested as "
"root. That is not supported because we cannot instrument a return "
"instruction to release the context: " +
F.getName());
return false;
}
auto &Head = F.getEntryBlock();
for (auto &I : Head) {
// Find the increment intrinsic in the entry basic block.
if (auto *Mark = dyn_cast<InstrProfIncrementInst>(&I)) {
assert(Mark->getIndex()->isZero());
IRBuilder<> Builder(Mark);
Guid = Builder.getInt64(
AssignGUIDPass::getGUID(cast<Function>(*Mark->getNameValue())));
// The type of the context of this function is now knowable since we have
// NumCallsites and NumCounters. We delcare it here because it's more
// convenient - we have the Builder.
ThisContextType = StructType::get(
F.getContext(),
{ContextNodeTy, ArrayType::get(Builder.getInt64Ty(), NumCounters),
ArrayType::get(Builder.getPtrTy(), NumCallsites)});
// Figure out which way we obtain the context object for this function -
// if it's an entrypoint, then we call StartCtx, otherwise GetCtx. In the
// former case, we also set TheRootFuctionData since we need to release it
// at the end (plus it can be used to know if we have an entrypoint or a
// regular function)
// Don't set a name, they end up taking a lot of space and we don't need
// them.
// Zero-initialize the FunctionData, except for functions that have
// musttail calls. There, we set the CtxRoot field to 1, which will be
// treated as a "can't be set as root".
TheRootFuctionData = new GlobalVariable(
M, FunctionDataTy, false, GlobalVariable::InternalLinkage,
HasMusttail ? CannotBeRootInitializer
: Constant::getNullValue(FunctionDataTy));
if (ContextRootSet.contains(&F)) {
Context = Builder.CreateCall(
StartCtx, {TheRootFuctionData, Guid, Builder.getInt32(NumCounters),
Builder.getInt32(NumCallsites)});
ORE.emit(
[&] { return OptimizationRemark(DEBUG_TYPE, "Entrypoint", &F); });
} else {
Context = Builder.CreateCall(GetCtx, {TheRootFuctionData, &F, Guid,
Builder.getInt32(NumCounters),
Builder.getInt32(NumCallsites)});
ORE.emit([&] {
return OptimizationRemark(DEBUG_TYPE, "RegularFunction", &F);
});
}
// The context could be scratch.
auto *CtxAsInt = Builder.CreatePtrToInt(Context, Builder.getInt64Ty());
if (NumCallsites > 0) {
// Figure out which index of the TLS 2-element buffers to use.
// Scratch context => we use index == 1. Real contexts => index == 0.
auto *Index = Builder.CreateAnd(CtxAsInt, Builder.getInt64(1));
// The GEPs corresponding to that index, in the respective TLS.
ExpectedCalleeTLSAddr = Builder.CreateGEP(
PointerType::getUnqual(F.getContext()),
Builder.CreateThreadLocalAddress(ExpectedCalleeTLS), {Index});
CallsiteInfoTLSAddr = Builder.CreateGEP(
Builder.getInt32Ty(),
Builder.CreateThreadLocalAddress(CallsiteInfoTLS), {Index});
}
// Because the context pointer may have LSB set (to indicate scratch),
// clear it for the value we use as base address for the counter vector.
// This way, if later we want to have "real" (not clobbered) buffers
// acting as scratch, the lowering (at least this part of it that deals
// with counters) stays the same.
RealContext = Builder.CreateIntToPtr(
Builder.CreateAnd(CtxAsInt, Builder.getInt64(-2)),
PointerType::getUnqual(F.getContext()));
I.eraseFromParent();
break;
}
}
if (!Context) {
ORE.emit([&] {
return OptimizationRemarkMissed(DEBUG_TYPE, "Skip", &F)
<< "Function doesn't have instrumentation, skipping";
});
return false;
}
bool ContextWasReleased = false;
for (auto &BB : F) {
for (auto &I : llvm::make_early_inc_range(BB)) {
if (auto *Instr = dyn_cast<InstrProfCntrInstBase>(&I)) {
IRBuilder<> Builder(Instr);
switch (Instr->getIntrinsicID()) {
case llvm::Intrinsic::instrprof_increment:
case llvm::Intrinsic::instrprof_increment_step: {
// Increments (or increment-steps) are just a typical load - increment
// - store in the RealContext.
auto *AsStep = cast<InstrProfIncrementInst>(Instr);
auto *GEP = Builder.CreateGEP(
ThisContextType, RealContext,
{Builder.getInt32(0), Builder.getInt32(1), AsStep->getIndex()});
Builder.CreateStore(
Builder.CreateAdd(Builder.CreateLoad(Builder.getInt64Ty(), GEP),
AsStep->getStep()),
GEP);
} break;
case llvm::Intrinsic::instrprof_callsite:
// callsite lowering: write the called value in the expected callee
// TLS we treat the TLS as volatile because of signal handlers and to
// avoid these being moved away from the callsite they decorate.
auto *CSIntrinsic = dyn_cast<InstrProfCallsite>(Instr);
Builder.CreateStore(CSIntrinsic->getCallee(), ExpectedCalleeTLSAddr,
true);
// write the GEP of the slot in the sub-contexts portion of the
// context in TLS. Now, here, we use the actual Context value - as
// returned from compiler-rt - which may have the LSB set if the
// Context was scratch. Since the header of the context object and
// then the values are all 8-aligned (or, really, insofar as we care,
// they are even) - if the context is scratch (meaning, an odd value),
// so will the GEP. This is important because this is then visible to
// compiler-rt which will produce scratch contexts for callers that
// have a scratch context.
Builder.CreateStore(
Builder.CreateGEP(ThisContextType, Context,
{Builder.getInt32(0), Builder.getInt32(2),
CSIntrinsic->getIndex()}),
CallsiteInfoTLSAddr, true);
break;
}
I.eraseFromParent();
} else if (!HasMusttail && isa<ReturnInst>(I)) {
// Remember to release the context if we are an entrypoint.
IRBuilder<> Builder(&I);
Builder.CreateCall(ReleaseCtx, {TheRootFuctionData});
ContextWasReleased = true;
}
}
}
if (!HasMusttail && !ContextWasReleased)
F.getContext().emitError(
"[ctx_prof] A function that doesn't have musttail calls was "
"instrumented but it has no `ret` "
"instructions above which to release the context: " +
F.getName());
return true;
}
PreservedAnalyses NoinlineNonPrevailing::run(Module &M,
ModuleAnalysisManager &MAM) {
bool Changed = false;
for (auto &F : M) {
if (F.isDeclaration())
continue;
if (F.hasFnAttribute(Attribute::NoInline))
continue;
if (!F.isWeakForLinker())
continue;
if (F.hasFnAttribute(Attribute::AlwaysInline))
F.removeFnAttr(Attribute::AlwaysInline);
F.addFnAttr(Attribute::NoInline);
Changed = true;
}
if (Changed)
return PreservedAnalyses::none();
return PreservedAnalyses::all();
}