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 #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
  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.
  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
  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.
  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