//===- NVVMReflect.cpp - NVVM Emulate conditional compilation -------------===//

//

// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.

// See https://llvm.org/LICENSE.txt for license information.

// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception

//

//===----------------------------------------------------------------------===//

//

// This pass replaces occurrences of __nvvm_reflect("foo") and llvm.nvvm.reflect

// with an integer.

//

// We choose the value we use by looking at metadata in the module itself.  Note

// that we intentionally only have one way to choose these values, because other

// parts of LLVM (particularly, InstCombineCall) rely on being able to predict

// the values chosen by this pass.

//

// If we see an unknown string, we replace its call with 0.

//

//===----------------------------------------------------------------------===//

#include "NVPTX.h"

#include "llvm/ADT/SmallVector.h"

#include "llvm/IR/Constants.h"

#include "llvm/IR/DerivedTypes.h"

#include "llvm/IR/Function.h"

#include "llvm/IR/InstIterator.h"

#include "llvm/IR/Instructions.h"

#include "llvm/IR/Intrinsics.h"

#include "llvm/IR/IntrinsicsNVPTX.h"

#include "llvm/IR/Module.h"

#include "llvm/IR/PassManager.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 <sstream>

#include <string>

#define NVVM_REFLECT_FUNCTION "__nvvm_reflect"

#define NVVM_REFLECT_OCL_FUNCTION "__nvvm_reflect_ocl"

using namespace llvm;

#define DEBUG_TYPE "nvptx-reflect"

namespace llvm { void initializeNVVMReflectPass(PassRegistry &); }

namespace {

class NVVMReflect : public FunctionPass {

public:

  static char ID;

  unsigned int SmVersion;

  NVVMReflect() : NVVMReflect(0) {}

  explicit NVVMReflect(unsigned int Sm) : FunctionPass(ID), SmVersion(Sm) {

    initializeNVVMReflectPass(*PassRegistry::getPassRegistry());

  }

  bool runOnFunction(Function &) override;

};

}

FunctionPass *llvm::createNVVMReflectPass(unsigned int SmVersion) {

  return new NVVMReflect(SmVersion);

}

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 bool runNVVMReflect(Function &F, unsigned SmVersion) {

  if (!NVVMReflectEnabled)

    return false;

  if (F.getName() == NVVM_REFLECT_FUNCTION ||

      F.getName() == NVVM_REFLECT_OCL_FUNCTION) {

    assert(F.isDeclaration() && "_reflect function should not have a body");

    assert(F.getReturnType()->isIntegerTy() &&

           "_reflect's return type should be integer");

    return false;

  }

  SmallVector<Instruction *, 4> ToRemove;

  // Go through the calls in this function.  Each call to __nvvm_reflect or

  // llvm.nvvm.reflect should be 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.

  // The 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)

  //

  // The 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 (Instruction &I : instructions(F)) {

    CallInst *Call = dyn_cast<CallInst>(&I);

    if (!Call)

      continue;

    Function *Callee = Call->getCalledFunction();

    if (!Callee || (Callee->getName() != NVVM_REFLECT_FUNCTION &&

                    Callee->getName() != NVVM_REFLECT_OCL_FUNCTION &&

                    Callee->getIntrinsicID() != Intrinsic::nvvm_reflect))

      continue;

    // FIXME: Improve error handling here and elsewhere in this pass.

    assert(Call->getNumOperands() == 2 &&

           "Wrong number of operands to __nvvm_reflect function");

    // In cuda 6.5 and earlier, we will have an extra constant-to-generic

    // conversion of the string.

    const Value *Str = Call->getArgOperand(0);

    if (const CallInst *ConvCall = dyn_cast<CallInst>(Str)) {

      // FIXME: Add assertions about ConvCall.

      Str = ConvCall->getArgOperand(0);

    }

    // Pre opaque pointers we have a constant expression wrapping the constant

    // string.

    Str = Str->stripPointerCasts();

    assert(isa<Constant>(Str) &&

           "Format of __nvvm_reflect function not recognized");

    const Value *Operand = cast<Constant>(Str)->getOperand(0);

    if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(Operand)) {

      // For CUDA-7.0 style __nvvm_reflect calls, we need to find the 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");

    StringRef ReflectArg = cast<ConstantDataSequential>(Operand)->getAsString();

    ReflectArg = ReflectArg.substr(0, ReflectArg.size() - 1);

    LLVM_DEBUG(dbgs() << "Arg of _reflect : " << ReflectArg << "\n");

    int ReflectVal = 0; // The default value is 0

    if (ReflectArg == "__CUDA_FTZ") {

      // Try to pull __CUDA_FTZ from the nvvm-reflect-ftz module flag.  Our

      // choice here must be kept in sync with AutoUpgrade, which uses the same

      // technique to detect whether ftz is enabled.

      if (auto *Flag = mdconst::extract_or_null<ConstantInt>(

              F.getParent()->getModuleFlag("nvvm-reflect-ftz")))

        ReflectVal = Flag->getSExtValue();

    } else if (ReflectArg == "__CUDA_ARCH") {

      ReflectVal = SmVersion * 10;

    }

    Call->replaceAllUsesWith(ConstantInt::get(Call->getType(), ReflectVal));

    ToRemove.push_back(Call);

  }

  for (Instruction *I : ToRemove)

    I->eraseFromParent();

  return ToRemove.size() > 0;

}

bool NVVMReflect::runOnFunction(Function &F) {

  return runNVVMReflect(F, SmVersion);

}

NVVMReflectPass::NVVMReflectPass() : NVVMReflectPass(0) {}

PreservedAnalyses NVVMReflectPass::run(Function &F,

                                       FunctionAnalysisManager &AM) {

  return runNVVMReflect(F, SmVersion) ? PreservedAnalyses::none()

                                      : PreservedAnalyses::all();

}