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(StubId);
40 }
41 
addSpeculationRuntime(JITDylib & JD,MangleAndInterner & Mangle)42 Error Speculator::addSpeculationRuntime(JITDylib &JD,
43                                         MangleAndInterner &Mangle) {
44   JITEvaluatedSymbol ThisPtr(pointerToJITTargetAddress(this),
45                              JITSymbolFlags::Exported);
46   JITEvaluatedSymbol SpeculateForEntryPtr(
47       pointerToJITTargetAddress(&speculateForEntryPoint),
48       JITSymbolFlags::Exported);
49   return JD.define(absoluteSymbols({
50       {Mangle("__orc_speculator"), ThisPtr},                // Data Symbol
51       {Mangle("__orc_speculate_for"), SpeculateForEntryPtr} // Callable Symbol
52   }));
53 }
54 
55 // If two modules, share the same LLVMContext, different threads must
56 // not access them concurrently without locking the associated LLVMContext
57 // this implementation follows this contract.
emit(std::unique_ptr<MaterializationResponsibility> R,ThreadSafeModule TSM)58 void IRSpeculationLayer::emit(std::unique_ptr<MaterializationResponsibility> R,
59                               ThreadSafeModule TSM) {
60 
61   assert(TSM && "Speculation Layer received Null Module ?");
62   assert(TSM.getContext().getContext() != nullptr &&
63          "Module with null LLVMContext?");
64 
65   // Instrumentation of runtime calls, lock the Module
66   TSM.withModuleDo([this, &R](Module &M) {
67     auto &MContext = M.getContext();
68     auto SpeculatorVTy = StructType::create(MContext, "Class.Speculator");
69     auto RuntimeCallTy = FunctionType::get(
70         Type::getVoidTy(MContext),
71         {SpeculatorVTy->getPointerTo(), Type::getInt64Ty(MContext)}, false);
72     auto RuntimeCall =
73         Function::Create(RuntimeCallTy, Function::LinkageTypes::ExternalLinkage,
74                          "__orc_speculate_for", &M);
75     auto SpeclAddr = new GlobalVariable(
76         M, SpeculatorVTy, false, GlobalValue::LinkageTypes::ExternalLinkage,
77         nullptr, "__orc_speculator");
78 
79     IRBuilder<> Mutator(MContext);
80 
81     // QueryAnalysis allowed to transform the IR source, one such example is
82     // Simplify CFG helps the static branch prediction heuristics!
83     for (auto &Fn : M.getFunctionList()) {
84       if (!Fn.isDeclaration()) {
85 
86         auto IRNames = QueryAnalysis(Fn);
87         // Instrument and register if Query has result
88         if (IRNames.hasValue()) {
89 
90           // Emit globals for each function.
91           auto LoadValueTy = Type::getInt8Ty(MContext);
92           auto SpeculatorGuard = new GlobalVariable(
93               M, LoadValueTy, false, GlobalValue::LinkageTypes::InternalLinkage,
94               ConstantInt::get(LoadValueTy, 0),
95               "__orc_speculate.guard.for." + Fn.getName());
96           SpeculatorGuard->setAlignment(Align(1));
97           SpeculatorGuard->setUnnamedAddr(GlobalValue::UnnamedAddr::Local);
98 
99           BasicBlock &ProgramEntry = Fn.getEntryBlock();
100           // Create BasicBlocks before the program's entry basicblock
101           BasicBlock *SpeculateBlock = BasicBlock::Create(
102               MContext, "__orc_speculate.block", &Fn, &ProgramEntry);
103           BasicBlock *SpeculateDecisionBlock = BasicBlock::Create(
104               MContext, "__orc_speculate.decision.block", &Fn, SpeculateBlock);
105 
106           assert(SpeculateDecisionBlock == &Fn.getEntryBlock() &&
107                  "SpeculateDecisionBlock not updated?");
108           Mutator.SetInsertPoint(SpeculateDecisionBlock);
109 
110           auto LoadGuard =
111               Mutator.CreateLoad(LoadValueTy, SpeculatorGuard, "guard.value");
112           // if just loaded value equal to 0,return true.
113           auto CanSpeculate =
114               Mutator.CreateICmpEQ(LoadGuard, ConstantInt::get(LoadValueTy, 0),
115                                    "compare.to.speculate");
116           Mutator.CreateCondBr(CanSpeculate, SpeculateBlock, &ProgramEntry);
117 
118           Mutator.SetInsertPoint(SpeculateBlock);
119           auto ImplAddrToUint =
120               Mutator.CreatePtrToInt(&Fn, Type::getInt64Ty(MContext));
121           Mutator.CreateCall(RuntimeCallTy, RuntimeCall,
122                              {SpeclAddr, ImplAddrToUint});
123           Mutator.CreateStore(ConstantInt::get(LoadValueTy, 1),
124                               SpeculatorGuard);
125           Mutator.CreateBr(&ProgramEntry);
126 
127           assert(Mutator.GetInsertBlock()->getParent() == &Fn &&
128                  "IR builder association mismatch?");
129           S.registerSymbols(internToJITSymbols(IRNames.getValue()),
130                             &R->getTargetJITDylib());
131         }
132       }
133     }
134   });
135 
136   assert(!TSM.withModuleDo([](const Module &M) { return verifyModule(M); }) &&
137          "Speculation Instrumentation breaks IR?");
138 
139   NextLayer.emit(std::move(R), std::move(TSM));
140 }
141 
142 } // namespace orc
143 } // namespace llvm
144