lib/Target/NVPTX/NVVMReflect.cpp

//===- NVVMReflect.cpp - NVVM Emulate conditional compilation -------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This pass replaces occurrences of __nvvm_reflect("string") with an
// integer based on -nvvm-reflect-list string=<int> option given to this pass.
// If an undefined string value is seen in a call to __nvvm_reflect("string"),
// a default value of 0 will be used.
//
//===----------------------------------------------------------------------===//

#include "NVPTX.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/StringMap.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/Intrinsics.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/Type.h"
#include "llvm/Pass.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_os_ostream.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/Scalar.h"
#include <map>
#include <sstream>
#include <string>
#include <vector>

#define NVVM_REFLECT_FUNCTION "__nvvm_reflect"

using namespace llvm;

#define DEBUG_TYPE "nvptx-reflect"

namespace llvm { void initializeNVVMReflectPass(PassRegistry &); }

namespace {
class NVVMReflect : public ModulePass {
private:
  StringMap<int> VarMap;
  typedef DenseMap<std::string, int>::iterator VarMapIter;

public:
  static char ID;
  NVVMReflect() : ModulePass(ID) {
    initializeNVVMReflectPass(*PassRegistry::getPassRegistry());
    VarMap.clear();
  }

  NVVMReflect(const StringMap<int> &Mapping)
  : ModulePass(ID) {
    initializeNVVMReflectPass(*PassRegistry::getPassRegistry());
    for (StringMap<int>::const_iterator I = Mapping.begin(), E = Mapping.end();
         I != E; ++I) {
      VarMap[(*I).getKey()] = (*I).getValue();
    }
  }

  void getAnalysisUsage(AnalysisUsage &AU) const override {
    AU.setPreservesAll();
  }
  bool runOnModule(Module &) override;

private:
  bool handleFunction(Function *ReflectFunction);
  void setVarMap();
};
}

ModulePass *llvm::createNVVMReflectPass() {
  return new NVVMReflect();
}

ModulePass *llvm::createNVVMReflectPass(const StringMap<int>& Mapping) {
  return new NVVMReflect(Mapping);
}

static cl::opt<bool>
NVVMReflectEnabled("nvvm-reflect-enable", cl::init(true), cl::Hidden,
                   cl::desc("NVVM reflection, enabled by default"));

char NVVMReflect::ID = 0;
INITIALIZE_PASS(NVVMReflect, "nvvm-reflect",
                "Replace occurrences of __nvvm_reflect() calls with 0/1", false,
                false)

static cl::list<std::string>
ReflectList("nvvm-reflect-list", cl::value_desc("name=<int>"), cl::Hidden,
            cl::desc("A list of string=num assignments"),
            cl::ValueRequired);

/// The command line can look as follows :
/// -nvvm-reflect-list a=1,b=2 -nvvm-reflect-list c=3,d=0 -R e=2
/// The strings "a=1,b=2", "c=3,d=0", "e=2" are available in the
/// ReflectList vector. First, each of ReflectList[i] is 'split'
/// using "," as the delimiter. Then each of this part is split
/// using "=" as the delimiter.
void NVVMReflect::setVarMap() {
  for (unsigned i = 0, e = ReflectList.size(); i != e; ++i) {
    DEBUG(dbgs() << "Option : "  << ReflectList[i] << "\n");
    SmallVector<StringRef, 4> NameValList;
    StringRef(ReflectList[i]).split(NameValList, ',');
    for (unsigned j = 0, ej = NameValList.size(); j != ej; ++j) {
      SmallVector<StringRef, 2> NameValPair;
      NameValList[j].split(NameValPair, '=');
      assert(NameValPair.size() == 2 && "name=val expected");
      std::stringstream ValStream(NameValPair[1]);
      int Val;
      ValStream >> Val;
      assert((!(ValStream.fail())) && "integer value expected");
      VarMap[NameValPair[0]] = Val;
    }
  }
}

bool NVVMReflect::handleFunction(Function *ReflectFunction) {
  // Validate _reflect function
  assert(ReflectFunction->isDeclaration() &&
         "_reflect function should not have a body");
  assert(ReflectFunction->getReturnType()->isIntegerTy() &&
         "_reflect's return type should be integer");

  std::vector<Instruction *> ToRemove;

  // Go through the uses of ReflectFunction in this Function.
  // Each of them should a CallInst with a ConstantArray argument.
  // First validate that. If the c-string corresponding to the
  // ConstantArray can be found successfully, see if it can be
  // found in VarMap. If so, replace the uses of CallInst with the
  // value found in VarMap. If not, replace the use  with value 0.

  // IR for __nvvm_reflect calls differs between CUDA versions:
  // CUDA 6.5 and earlier uses this sequence:
  //    %ptr = tail call i8* @llvm.nvvm.ptr.constant.to.gen.p0i8.p4i8
  //        (i8 addrspace(4)* getelementptr inbounds
  //           ([8 x i8], [8 x i8] addrspace(4)* @str, i32 0, i32 0))
  //    %reflect = tail call i32 @__nvvm_reflect(i8* %ptr)
  //
  // Value returned by Sym->getOperand(0) is a Constant with a
  // ConstantDataSequential operand which can be converted to string and used
  // for lookup.
  //
  // CUDA 7.0 does it slightly differently:
  //   %reflect = call i32 @__nvvm_reflect(i8* addrspacecast
  //        (i8 addrspace(1)* getelementptr inbounds
  //           ([8 x i8], [8 x i8] addrspace(1)* @str, i32 0, i32 0) to i8*))
  //
  // In this case, we get a Constant with a GlobalVariable operand and we need
  // to dig deeper to find its initializer with the string we'll use for lookup.

  for (User *U : ReflectFunction->users()) {
    assert(isa<CallInst>(U) && "Only a call instruction can use _reflect");
    CallInst *Reflect = cast<CallInst>(U);

    assert((Reflect->getNumOperands() == 2) &&
           "Only one operand expect for _reflect function");
    // In cuda, we will have an extra constant-to-generic conversion of
    // the string.
    const Value *Str = Reflect->getArgOperand(0);
    if (isa<CallInst>(Str)) {
      // CUDA path
      const CallInst *ConvCall = cast<CallInst>(Str);
      Str = ConvCall->getArgOperand(0);
    }
    assert(isa<ConstantExpr>(Str) &&
           "Format of _reflect function not recognized");
    const ConstantExpr *GEP = cast<ConstantExpr>(Str);

    const Value *Sym = GEP->getOperand(0);
    assert(isa<Constant>(Sym) && "Format of _reflect function not recognized");

    const Value *Operand = cast<Constant>(Sym)->getOperand(0);
    if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(Operand)) {
      // For CUDA-7.0 style __nvvm_reflect calls we need to find operand's
      // initializer.
      assert(GV->hasInitializer() &&
             "Format of _reflect function not recognized");
      const Constant *Initializer = GV->getInitializer();
      Operand = Initializer;
    }

    assert(isa<ConstantDataSequential>(Operand) &&
           "Format of _reflect function not recognized");
    assert(cast<ConstantDataSequential>(Operand)->isCString() &&
           "Format of _reflect function not recognized");

    std::string ReflectArg =
        cast<ConstantDataSequential>(Operand)->getAsString();

    ReflectArg = ReflectArg.substr(0, ReflectArg.size() - 1);
    DEBUG(dbgs() << "Arg of _reflect : " << ReflectArg << "\n");

    int ReflectVal = 0; // The default value is 0
    if (VarMap.find(ReflectArg) != VarMap.end()) {
      ReflectVal = VarMap[ReflectArg];
    }
    Reflect->replaceAllUsesWith(
        ConstantInt::get(Reflect->getType(), ReflectVal));
    ToRemove.push_back(Reflect);
  }
  if (ToRemove.size() == 0)
    return false;

  for (unsigned i = 0, e = ToRemove.size(); i != e; ++i)
    ToRemove[i]->eraseFromParent();
  return true;
}

bool NVVMReflect::runOnModule(Module &M) {
  if (!NVVMReflectEnabled)
    return false;

  setVarMap();


  bool Res = false;
  std::string Name;
  Type *Tys[1];
  Type *I8Ty = Type::getInt8Ty(M.getContext());
  Function *ReflectFunction;

  // Check for standard overloaded versions of llvm.nvvm.reflect

  for (unsigned i = 0; i != 5; ++i) {
    Tys[0] = PointerType::get(I8Ty, i);
    Name = Intrinsic::getName(Intrinsic::nvvm_reflect, Tys);
    ReflectFunction = M.getFunction(Name);
    if(ReflectFunction != 0) {
      Res |= handleFunction(ReflectFunction);
    }
  }

  ReflectFunction = M.getFunction(NVVM_REFLECT_FUNCTION);
  // If reflect function is not used, then there will be
  // no entry in the module.
  if (ReflectFunction != 0)
    Res |= handleFunction(ReflectFunction);

  return Res;
}