1 //===---------- speculation.cpp - Utilities for Speculation ----------===//
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 #include "llvm/ExecutionEngine/Orc/Speculation.h"
10 #include "llvm/IR/BasicBlock.h"
11 #include "llvm/IR/Function.h"
12 #include "llvm/IR/IRBuilder.h"
13 #include "llvm/IR/Instruction.h"
14 #include "llvm/IR/Instructions.h"
15 #include "llvm/IR/LLVMContext.h"
16 #include "llvm/IR/Module.h"
17 #include "llvm/IR/Type.h"
18 #include "llvm/IR/Verifier.h"
19
20 namespace llvm {
21
22 namespace orc {
23
24 // ImplSymbolMap methods
trackImpls(SymbolAliasMap ImplMaps,JITDylib * SrcJD)25 void ImplSymbolMap::trackImpls(SymbolAliasMap ImplMaps, JITDylib *SrcJD) {
26 assert(SrcJD && "Tracking on Null Source .impl dylib");
27 std::lock_guard<std::mutex> Lockit(ConcurrentAccess);
28 for (auto &I : ImplMaps) {
29 auto It = Maps.insert({I.first, {I.second.Aliasee, SrcJD}});
30 // check rationale when independent dylibs have same symbol name?
31 assert(It.second && "ImplSymbols are already tracked for this Symbol?");
32 (void)(It);
33 }
34 }
35
36 // Trigger Speculative Compiles.
speculateForEntryPoint(Speculator * Ptr,uint64_t StubId)37 void Speculator::speculateForEntryPoint(Speculator *Ptr, uint64_t StubId) {
38 assert(Ptr && " Null Address Received in orc_speculate_for ");
39 Ptr->speculateFor(ExecutorAddr(StubId));
40 }
41
addSpeculationRuntime(JITDylib & JD,MangleAndInterner & Mangle)42 Error Speculator::addSpeculationRuntime(JITDylib &JD,
43 MangleAndInterner &Mangle) {
44 ExecutorSymbolDef ThisPtr(ExecutorAddr::fromPtr(this),
45 JITSymbolFlags::Exported);
46 ExecutorSymbolDef SpeculateForEntryPtr(
47 ExecutorAddr::fromPtr(&speculateForEntryPoint), JITSymbolFlags::Exported);
48 return JD.define(absoluteSymbols({
49 {Mangle("__orc_speculator"), ThisPtr}, // Data Symbol
50 {Mangle("__orc_speculate_for"), SpeculateForEntryPtr} // Callable Symbol
51 }));
52 }
53
54 // If two modules, share the same LLVMContext, different threads must
55 // not access them concurrently without locking the associated LLVMContext
56 // this implementation follows this contract.
emit(std::unique_ptr<MaterializationResponsibility> R,ThreadSafeModule TSM)57 void IRSpeculationLayer::emit(std::unique_ptr<MaterializationResponsibility> R,
58 ThreadSafeModule TSM) {
59
60 assert(TSM && "Speculation Layer received Null Module ?");
61 assert(TSM.getContext().getContext() != nullptr &&
62 "Module with null LLVMContext?");
63
64 // Instrumentation of runtime calls, lock the Module
65 TSM.withModuleDo([this, &R](Module &M) {
66 auto &MContext = M.getContext();
67 auto SpeculatorVTy = StructType::create(MContext, "Class.Speculator");
68 auto RuntimeCallTy = FunctionType::get(
69 Type::getVoidTy(MContext),
70 {PointerType::getUnqual(MContext), Type::getInt64Ty(MContext)}, false);
71 auto RuntimeCall =
72 Function::Create(RuntimeCallTy, Function::LinkageTypes::ExternalLinkage,
73 "__orc_speculate_for", &M);
74 auto SpeclAddr = new GlobalVariable(
75 M, SpeculatorVTy, false, GlobalValue::LinkageTypes::ExternalLinkage,
76 nullptr, "__orc_speculator");
77
78 IRBuilder<> Mutator(MContext);
79
80 // QueryAnalysis allowed to transform the IR source, one such example is
81 // Simplify CFG helps the static branch prediction heuristics!
82 for (auto &Fn : M.getFunctionList()) {
83 if (!Fn.isDeclaration()) {
84
85 auto IRNames = QueryAnalysis(Fn);
86 // Instrument and register if Query has result
87 if (IRNames) {
88
89 // Emit globals for each function.
90 auto LoadValueTy = Type::getInt8Ty(MContext);
91 auto SpeculatorGuard = new GlobalVariable(
92 M, LoadValueTy, false, GlobalValue::LinkageTypes::InternalLinkage,
93 ConstantInt::get(LoadValueTy, 0),
94 "__orc_speculate.guard.for." + Fn.getName());
95 SpeculatorGuard->setAlignment(Align(1));
96 SpeculatorGuard->setUnnamedAddr(GlobalValue::UnnamedAddr::Local);
97
98 BasicBlock &ProgramEntry = Fn.getEntryBlock();
99 // Create BasicBlocks before the program's entry basicblock
100 BasicBlock *SpeculateBlock = BasicBlock::Create(
101 MContext, "__orc_speculate.block", &Fn, &ProgramEntry);
102 BasicBlock *SpeculateDecisionBlock = BasicBlock::Create(
103 MContext, "__orc_speculate.decision.block", &Fn, SpeculateBlock);
104
105 assert(SpeculateDecisionBlock == &Fn.getEntryBlock() &&
106 "SpeculateDecisionBlock not updated?");
107 Mutator.SetInsertPoint(SpeculateDecisionBlock);
108
109 auto LoadGuard =
110 Mutator.CreateLoad(LoadValueTy, SpeculatorGuard, "guard.value");
111 // if just loaded value equal to 0,return true.
112 auto CanSpeculate =
113 Mutator.CreateICmpEQ(LoadGuard, ConstantInt::get(LoadValueTy, 0),
114 "compare.to.speculate");
115 Mutator.CreateCondBr(CanSpeculate, SpeculateBlock, &ProgramEntry);
116
117 Mutator.SetInsertPoint(SpeculateBlock);
118 auto ImplAddrToUint =
119 Mutator.CreatePtrToInt(&Fn, Type::getInt64Ty(MContext));
120 Mutator.CreateCall(RuntimeCallTy, RuntimeCall,
121 {SpeclAddr, ImplAddrToUint});
122 Mutator.CreateStore(ConstantInt::get(LoadValueTy, 1),
123 SpeculatorGuard);
124 Mutator.CreateBr(&ProgramEntry);
125
126 assert(Mutator.GetInsertBlock()->getParent() == &Fn &&
127 "IR builder association mismatch?");
128 S.registerSymbols(internToJITSymbols(*IRNames),
129 &R->getTargetJITDylib());
130 }
131 }
132 }
133 });
134
135 assert(!TSM.withModuleDo([](const Module &M) { return verifyModule(M); }) &&
136 "Speculation Instrumentation breaks IR?");
137
138 NextLayer.emit(std::move(R), std::move(TSM));
139 }
140
141 } // namespace orc
142 } // namespace llvm
143