lib/ExecutionEngine/Orc/Speculation.cpp

   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 #include "llvm/Support/Debug.h"
  20
  21 #include <vector>
  22
  23 namespace llvm {
  24
  25 namespace orc {
  26
  27 // ImplSymbolMap methods
  28 void ImplSymbolMap::trackImpls(SymbolAliasMap ImplMaps, JITDylib *SrcJD) {
  29   assert(SrcJD && "Tracking on Null Source .impl dylib");
  30   std::lock_guard<std::mutex> Lockit(ConcurrentAccess);
  31   for (auto &I : ImplMaps) {
  32     auto It = Maps.insert({I.first, {I.second.Aliasee, SrcJD}});
  33     // check rationale when independent dylibs have same symbol name?
  34     assert(It.second && "ImplSymbols are already tracked for this Symbol?");
  35     (void)(It);
  36   }
  37 }
  38
  39 // Trigger Speculative Compiles.
  40 void Speculator::speculateForEntryPoint(Speculator *Ptr, uint64_t StubId) {
  41   assert(Ptr && " Null Address Received in orc_speculate_for ");
  42   Ptr->speculateFor(StubId);
  43 }
  44
  45 Error Speculator::addSpeculationRuntime(JITDylib &JD,
  46                                         MangleAndInterner &Mangle) {
  47   JITEvaluatedSymbol ThisPtr(pointerToJITTargetAddress(this),
  48                              JITSymbolFlags::Exported);
  49   JITEvaluatedSymbol SpeculateForEntryPtr(
  50       pointerToJITTargetAddress(&speculateForEntryPoint),
  51       JITSymbolFlags::Exported);
  52   return JD.define(absoluteSymbols({
  53       {Mangle("__orc_speculator"), ThisPtr},                // Data Symbol
  54       {Mangle("__orc_speculate_for"), SpeculateForEntryPtr} // Callable Symbol
  55   }));
  56 }
  57
  58 // If two modules, share the same LLVMContext, different threads must
  59 // not access them concurrently without locking the associated LLVMContext
  60 // this implementation follows this contract.
  61 void IRSpeculationLayer::emit(MaterializationResponsibility R,
  62                               ThreadSafeModule TSM) {
  63
  64   assert(TSM && "Speculation Layer received Null Module ?");
  65   assert(TSM.getContext().getContext() != nullptr &&
  66          "Module with null LLVMContext?");
  67
  68   // Instrumentation of runtime calls, lock the Module
  69   TSM.withModuleDo([this, &R](Module &M) {
  70     auto &MContext = M.getContext();
  71     auto SpeculatorVTy = StructType::create(MContext, "Class.Speculator");
  72     auto RuntimeCallTy = FunctionType::get(
  73         Type::getVoidTy(MContext),
  74         {SpeculatorVTy->getPointerTo(), Type::getInt64Ty(MContext)}, false);
  75     auto RuntimeCall =
  76         Function::Create(RuntimeCallTy, Function::LinkageTypes::ExternalLinkage,
  77                          "__orc_speculate_for", &M);
  78     auto SpeclAddr = new GlobalVariable(
  79         M, SpeculatorVTy, false, GlobalValue::LinkageTypes::ExternalLinkage,
  80         nullptr, "__orc_speculator");
  81
  82     IRBuilder<> Mutator(MContext);
  83
  84     // QueryAnalysis allowed to transform the IR source, one such example is
  85     // Simplify CFG helps the static branch prediction heuristics!
  86     for (auto &Fn : M.getFunctionList()) {
  87       if (!Fn.isDeclaration()) {
  88
  89         auto IRNames = QueryAnalysis(Fn);
  90         // Instrument and register if Query has result
  91         if (IRNames.hasValue()) {
  92
  93           // Emit globals for each function.
  94           auto LoadValueTy = Type::getInt8Ty(MContext);
  95           auto SpeculatorGuard = new GlobalVariable(
  96               M, LoadValueTy, false, GlobalValue::LinkageTypes::InternalLinkage,
  97               ConstantInt::get(LoadValueTy, 0),
  98               "__orc_speculate.guard.for." + Fn.getName());
  99           SpeculatorGuard->setAlignment(Align::None());
 100           SpeculatorGuard->setUnnamedAddr(GlobalValue::UnnamedAddr::Local);
 101
 102           BasicBlock &ProgramEntry = Fn.getEntryBlock();
 103           // Create BasicBlocks before the program's entry basicblock
 104           BasicBlock *SpeculateBlock = BasicBlock::Create(
 105               MContext, "__orc_speculate.block", &Fn, &ProgramEntry);
 106           BasicBlock *SpeculateDecisionBlock = BasicBlock::Create(
 107               MContext, "__orc_speculate.decision.block", &Fn, SpeculateBlock);
 108
 109           assert(SpeculateDecisionBlock == &Fn.getEntryBlock() &&
 110                  "SpeculateDecisionBlock not updated?");
 111           Mutator.SetInsertPoint(SpeculateDecisionBlock);
 112
 113           auto LoadGuard =
 114               Mutator.CreateLoad(LoadValueTy, SpeculatorGuard, "guard.value");
 115           // if just loaded value equal to 0,return true.
 116           auto CanSpeculate =
 117               Mutator.CreateICmpEQ(LoadGuard, ConstantInt::get(LoadValueTy, 0),
 118                                    "compare.to.speculate");
 119           Mutator.CreateCondBr(CanSpeculate, SpeculateBlock, &ProgramEntry);
 120
 121           Mutator.SetInsertPoint(SpeculateBlock);
 122           auto ImplAddrToUint =
 123               Mutator.CreatePtrToInt(&Fn, Type::getInt64Ty(MContext));
 124           Mutator.CreateCall(RuntimeCallTy, RuntimeCall,
 125                              {SpeclAddr, ImplAddrToUint});
 126           Mutator.CreateStore(ConstantInt::get(LoadValueTy, 1),
 127                               SpeculatorGuard);
 128           Mutator.CreateBr(&ProgramEntry);
 129
 130           assert(Mutator.GetInsertBlock()->getParent() == &Fn &&
 131                  "IR builder association mismatch?");
 132           S.registerSymbols(internToJITSymbols(IRNames.getValue()),
 133                             &R.getTargetJITDylib());
 134         }
 135       }
 136     }
 137   });
 138
 139   assert(!TSM.withModuleDo([](const Module &M) { return verifyModule(M); }) &&
 140          "Speculation Instrumentation breaks IR?");
 141
 142   NextLayer.emit(std::move(R), std::move(TSM));
 143 }
 144
 145 } // namespace orc
 146 } // namespace llvm