SPIRVRegularizeLLVM.cpp

//===- SPIRVRegularizeLLVM.cpp - Regularize LLVM for SPIR-V ------- C++ -*-===//
//
//                     The LLVM/SPIRV Translator
//
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//===----------------------------------------------------------------------===//
//
// This file implements regularization of LLVM moduel for SPIR-V.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "spvregular"

#include "OCLUtil.h"
#include "SPIRVInternal.h"
#include "SPIRVMDBuilder.h"
#include "SPIRVMDWalker.h"

#include "llvm/ADT/StringSwitch.h"
#include "llvm/ADT/Triple.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/InstVisitor.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/Verifier.h"
#include "llvm/Pass.h"
#include "llvm/PassSupport.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"

#include <set>

using namespace llvm;
using namespace SPIRV;
using namespace OCLUtil;

namespace SPIRV {

static bool SPIRVDbgSaveRegularizedModule = false;
static std::string RegularizedModuleTmpFile = "regularized.bc";

class SPIRVRegularizeLLVM : public ModulePass {
public:
  SPIRVRegularizeLLVM() : ModulePass(ID), M(nullptr), Ctx(nullptr) {
    initializeSPIRVRegularizeLLVMPass(*PassRegistry::getPassRegistry());
  }

  bool runOnModule(Module &M) override;

  // Lower functions
  bool regularize();

  /// Erase cast inst of function and replace with the function.
  /// Assuming F is a SPIR-V builtin function with op code \param OC.
  void lowerFuncPtr(Function *F, Op OC);
  void lowerFuncPtr(Module *M);

  static char ID;

private:
  Module *M;
  LLVMContext *Ctx;
};

char SPIRVRegularizeLLVM::ID = 0;

bool SPIRVRegularizeLLVM::runOnModule(Module &Module) {
  M = &Module;
  Ctx = &M->getContext();

  LLVM_DEBUG(dbgs() << "Enter SPIRVRegularizeLLVM:\n");
  regularize();

  LLVM_DEBUG(dbgs() << "After SPIRVRegularizeLLVM:\n" << *M);
  std::string Err;
  raw_string_ostream ErrorOS(Err);
  if (verifyModule(*M, &ErrorOS)) {
    LLVM_DEBUG(errs() << "Fails to verify module: " << ErrorOS.str());
  }
  return true;
}

/// Remove entities not representable by SPIR-V
bool SPIRVRegularizeLLVM::regularize() {
  LLVMContext *Context = &M->getContext();

  eraseUselessFunctions(M);
  lowerFuncPtr(M);
  // lowerConstantExpressions();

  for (auto I = M->begin(), E = M->end(); I != E;) {
    Function *F = &(*I++);
    if (F->isDeclaration() && F->use_empty()) {
      F->eraseFromParent();
      continue;
    }

    for (auto BI = F->begin(), BE = F->end(); BI != BE; ++BI) {
      for (auto II = BI->begin(), IE = BI->end(); II != IE; ++II) {
        if (auto Call = dyn_cast<CallInst>(II)) {
          Call->setTailCall(false);
          Function *CF = Call->getCalledFunction();
          if (CF && CF->isIntrinsic())
            removeFnAttr(Context, Call, Attribute::NoUnwind);
        }

        // Remove optimization info not supported by SPIRV
        if (auto BO = dyn_cast<BinaryOperator>(II)) {
          if (isa<PossiblyExactOperator>(BO) && BO->isExact())
            BO->setIsExact(false);
        }
        // Remove metadata not supported by SPIRV
        static const char *MDs[] = {
            "fpmath",
            "tbaa",
            "range",
        };
        for (auto &MDName : MDs) {
          if (II->getMetadata(MDName)) {
            II->setMetadata(MDName, nullptr);
          }
        }
      }
    }
  }

  std::string Err;
  raw_string_ostream ErrorOS(Err);
  if (verifyModule(*M, &ErrorOS)) {
    SPIRVDBG(errs() << "Fails to verify module: " << ErrorOS.str();)
    return false;
  }

  if (SPIRVDbgSaveRegularizedModule)
    saveLLVMModule(M, RegularizedModuleTmpFile);
  return true;
}

// Assume F is a SPIR-V builtin function with a function pointer argument which
// is a bitcast instruction casting a function to a void(void) function pointer.
void SPIRVRegularizeLLVM::lowerFuncPtr(Function *F, Op OC) {
  LLVM_DEBUG(dbgs() << "[lowerFuncPtr] " << *F << '\n');
  auto Name = decorateSPIRVFunction(getName(OC));
  std::set<Value *> InvokeFuncPtrs;
  auto Attrs = F->getAttributes();
  mutateFunction(
      F,
      [=, &InvokeFuncPtrs](CallInst *CI, std::vector<Value *> &Args) {
        for (auto &I : Args) {
          if (isFunctionPointerType(I->getType())) {
            InvokeFuncPtrs.insert(I);
            I = removeCast(I);
          }
        }
        return Name;
      },
      nullptr, &Attrs, false);
  for (auto &I : InvokeFuncPtrs)
    eraseIfNoUse(I);
}

void SPIRVRegularizeLLVM::lowerFuncPtr(Module *M) {
  std::vector<std::pair<Function *, Op>> Work;
  for (auto &F : *M) {
    auto AI = F.arg_begin();
    if (hasFunctionPointerArg(&F, AI)) {
      auto OC = getSPIRVFuncOC(F.getName());
      assert(OC != OpNop && "Invalid function pointer usage");
      Work.push_back(std::make_pair(&F, OC));
    }
  }
  for (auto &I : Work)
    lowerFuncPtr(I.first, I.second);
}

} // namespace SPIRV

INITIALIZE_PASS(SPIRVRegularizeLLVM, "spvregular", "Regularize LLVM for SPIR-V",
                false, false)

ModulePass *llvm::createSPIRVRegularizeLLVM() {
  return new SPIRVRegularizeLLVM();
}