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