DXILPrepare.cpp

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//===- DXILPrepare.cpp - Prepare LLVM Module for DXIL encoding ------------===//
//
// 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
//
//===----------------------------------------------------------------------===//
///
/// \file This file contains pases and utilities to convert a modern LLVM
/// module into a module compatible with the LLVM 3.7-based DirectX Intermediate
/// Language (DXIL).
//===----------------------------------------------------------------------===//
 
#include "DirectX.h"
#include "PointerTypeAnalysis.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/Instruction.h"
#include "llvm/IR/Module.h"
#include "llvm/InitializePasses.h"
#include "llvm/Pass.h"
#include "llvm/Support/Compiler.h"
 
#define DEBUG_TYPE "dxil-prepare"
 
using namespace llvm;
using namespace llvm::dxil;
 
namespace {
 
constexpr bool isValidForDXIL(Attribute::AttrKind Attr) {
  return is_contained({Attribute::Alignment,
                       Attribute::AlwaysInline,
                       Attribute::Builtin,
                       Attribute::ByVal,
                       Attribute::InAlloca,
                       Attribute::Cold,
                       Attribute::Convergent,
                       Attribute::InlineHint,
                       Attribute::InReg,
                       Attribute::JumpTable,
                       Attribute::MinSize,
                       Attribute::Naked,
                       Attribute::Nest,
                       Attribute::NoAlias,
                       Attribute::NoBuiltin,
                       Attribute::NoCapture,
                       Attribute::NoDuplicate,
                       Attribute::NoImplicitFloat,
                       Attribute::NoInline,
                       Attribute::NonLazyBind,
                       Attribute::NonNull,
                       Attribute::Dereferenceable,
                       Attribute::DereferenceableOrNull,
                       Attribute::NoRedZone,
                       Attribute::NoReturn,
                       Attribute::NoUnwind,
                       Attribute::OptimizeForSize,
                       Attribute::OptimizeNone,
                       Attribute::ReadNone,
                       Attribute::ReadOnly,
                       Attribute::ArgMemOnly,
                       Attribute::Returned,
                       Attribute::ReturnsTwice,
                       Attribute::SExt,
                       Attribute::StackAlignment,
                       Attribute::StackProtect,
                       Attribute::StackProtectReq,
                       Attribute::StackProtectStrong,
                       Attribute::SafeStack,
                       Attribute::StructRet,
                       Attribute::SanitizeAddress,
                       Attribute::SanitizeThread,
                       Attribute::SanitizeMemory,
                       Attribute::UWTable,
                       Attribute::ZExt},
                      Attr);
}
 
class DXILPrepareModule : public ModulePass {
 
  static Value *maybeGenerateBitcast(IRBuilder<> &Builder,
                                     PointerTypeMap &PointerTypes,
                                     Instruction &Inst, Value *Operand,
                                     Type *Ty) {
    // Omit bitcasts if the incoming value matches the instruction type.
    auto It = PointerTypes.find(Operand);
    if (It != PointerTypes.end())
      if (cast<TypedPointerType>(It->second)->getElementType() == Ty)
        return nullptr;
    // Insert bitcasts where we are removing the instruction.
    Builder.SetInsertPoint(&Inst);
    // This code only gets hit in opaque-pointer mode, so the type of the
    // pointer doesn't matter.
    PointerType *PtrTy = cast<PointerType>(Operand->getType());
    return Builder.Insert(
        CastInst::Create(Instruction::BitCast, Operand,
                         Builder.getInt8PtrTy(PtrTy->getAddressSpace())));
  }
 
public:
  bool runOnModule(Module &M) override {
    PointerTypeMap PointerTypes = PointerTypeAnalysis::run(M);
    AttributeMask AttrMask;
    for (Attribute::AttrKind I = Attribute::None; I != Attribute::EndAttrKinds;
         I = Attribute::AttrKind(I + 1)) {
      if (!isValidForDXIL(I))
        AttrMask.addAttribute(I);
    }
    for (auto &F : M.functions()) {
      F.removeFnAttrs(AttrMask);
      F.removeRetAttrs(AttrMask);
      for (size_t Idx = 0, End = F.arg_size(); Idx < End; ++Idx)
        F.removeParamAttrs(Idx, AttrMask);
 
      for (auto &BB : F) {
        IRBuilder<> Builder(&BB);
        for (auto &I : make_early_inc_range(BB)) {
          if (I.getOpcode() == Instruction::FNeg) {
            Builder.SetInsertPoint(&I);
            Value *In = I.getOperand(0);
            Value *Zero = ConstantFP::get(In->getType(), -0.0);
            I.replaceAllUsesWith(Builder.CreateFSub(Zero, In));
            I.eraseFromParent();
            continue;
          }
          // Only insert bitcasts if the IR is using opaque pointers.
          if (M.getContext().supportsTypedPointers())
            continue;
 
          // Emtting NoOp bitcast instructions allows the ValueEnumerator to be
          // unmodified as it reserves instruction IDs during contruction.
          if (auto LI = dyn_cast<LoadInst>(&I)) {
            if (Value *NoOpBitcast = maybeGenerateBitcast(
                    Builder, PointerTypes, I, LI->getPointerOperand(),
                    LI->getType())) {
              LI->replaceAllUsesWith(
                  Builder.CreateLoad(LI->getType(), NoOpBitcast));
              LI->eraseFromParent();
            }
            continue;
          }
          if (auto SI = dyn_cast<StoreInst>(&I)) {
            if (Value *NoOpBitcast = maybeGenerateBitcast(
                    Builder, PointerTypes, I, SI->getPointerOperand(),
                    SI->getValueOperand()->getType())) {
 
              SI->replaceAllUsesWith(
                  Builder.CreateStore(SI->getValueOperand(), NoOpBitcast));
              SI->eraseFromParent();
            }
            continue;
          }
          if (auto GEP = dyn_cast<GetElementPtrInst>(&I)) {
            if (Value *NoOpBitcast = maybeGenerateBitcast(
                    Builder, PointerTypes, I, GEP->getPointerOperand(),
                    GEP->getResultElementType()))
              GEP->setOperand(0, NoOpBitcast);
            continue;
          }
          if (auto *CB = dyn_cast<CallBase>(&I)) {
            CB->removeFnAttrs(AttrMask);
            CB->removeRetAttrs(AttrMask);
            for (size_t Idx = 0, End = CB->arg_size(); Idx < End; ++Idx)
              CB->removeParamAttrs(Idx, AttrMask);
            continue;
          }
        }
      }
    }
    return true;
  }
 
  DXILPrepareModule() : ModulePass(ID) {}
 
  static char ID; // Pass identification.
};
char DXILPrepareModule::ID = 0;
 
} // end anonymous namespace
 
INITIALIZE_PASS_BEGIN(DXILPrepareModule, DEBUG_TYPE, "DXIL Prepare Module",
                      false, false)
INITIALIZE_PASS_END(DXILPrepareModule, DEBUG_TYPE, "DXIL Prepare Module", false,
                    false)
 
ModulePass *llvm::createDXILPrepareModulePass() {
  return new DXILPrepareModule();
}