lib/HLSL/DxilPrecisePropagatePass.cpp

///////////////////////////////////////////////////////////////////////////////
//                                                                           //
// DxilPrecisePropagatePass.cpp                                              //
// Copyright (C) Microsoft Corporation. All rights reserved.                 //
// This file is distributed under the University of Illinois Open Source     //
// License. See LICENSE.TXT for details.                                     //
//                                                                           //
///////////////////////////////////////////////////////////////////////////////

#include "dxc/DXIL/DxilModule.h"
#include "dxc/HLSL/DxilGenerationPass.h"
#include "dxc/HLSL/HLModule.h"
#include "dxc/HLSL/HLOperations.h"
#include "llvm/Pass.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/Instruction.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/Operator.h"
#include "llvm/IR/Module.h"
#include "llvm/Support/Casting.h"
#include <unordered_set>
#include <vector>

using namespace llvm;
using namespace hlsl;

namespace {
class DxilPrecisePropagatePass : public ModulePass {
public:
  static char ID; // Pass identification, replacement for typeid
  explicit DxilPrecisePropagatePass() : ModulePass(ID) {}

  const char *getPassName() const override { return "DXIL Precise Propagate"; }

  bool runOnModule(Module &M) override {
    DxilModule &dxilModule = M.GetOrCreateDxilModule();
    DxilTypeSystem &typeSys = dxilModule.GetTypeSystem();
    std::unordered_set<Instruction*> processedSet;
    std::vector<Function*> deadList;
    for (Function &F : M.functions()) {
      if (HLModule::HasPreciseAttribute(&F)) {
        PropagatePreciseOnFunctionUser(F, typeSys, processedSet);
        deadList.emplace_back(&F);
      }
    }
    for (Function *F : deadList)
      F->eraseFromParent();
    return true;
  }

private:
  void PropagatePreciseOnFunctionUser(
      Function &F, DxilTypeSystem &typeSys,
      std::unordered_set<Instruction *> &processedSet);
};

char DxilPrecisePropagatePass::ID = 0;

}

static void PropagatePreciseAttribute(Instruction *I, DxilTypeSystem &typeSys,
    std::unordered_set<Instruction *> &processedSet);

static void PropagatePreciseAttributeOnOperand(
    Value *V, DxilTypeSystem &typeSys, LLVMContext &Context,
    std::unordered_set<Instruction *> &processedSet) {
  Instruction *I = dyn_cast<Instruction>(V);
  // Skip none inst.
  if (!I)
    return;

  FPMathOperator *FPMath = dyn_cast<FPMathOperator>(I);
  // Skip none FPMath
  if (!FPMath)
    return;

  // Skip inst already marked.
  if (processedSet.count(I) > 0)
    return;
  // TODO: skip precise on integer type, sample instruction...
  processedSet.insert(I);
  // Set precise fast math on those instructions that support it.
  if (DxilModule::PreservesFastMathFlags(I))
    DxilModule::SetPreciseFastMathFlags(I);

  // Fast math not work on call, use metadata.
  if (CallInst *CI = dyn_cast<CallInst>(I))
    HLModule::MarkPreciseAttributeWithMetadata(CI);
  PropagatePreciseAttribute(I, typeSys, processedSet);
}

static void PropagatePreciseAttributeOnPointer(
    Value *Ptr, DxilTypeSystem &typeSys, LLVMContext &Context,
    std::unordered_set<Instruction *> &processedSet) {
  // Find all store and propagate on the val operand of store.
  // For CallInst, if Ptr is used as out parameter, mark it.
  for (User *U : Ptr->users()) {
    Instruction *user = cast<Instruction>(U);
    if (StoreInst *stInst = dyn_cast<StoreInst>(user)) {
      Value *val = stInst->getValueOperand();
      PropagatePreciseAttributeOnOperand(val, typeSys, Context, processedSet);
    } else if (CallInst *CI = dyn_cast<CallInst>(user)) {
      bool bReadOnly = true;

      Function *F = CI->getCalledFunction();
      const DxilFunctionAnnotation *funcAnnotation =
          typeSys.GetFunctionAnnotation(F);
      for (unsigned i = 0; i < CI->getNumArgOperands(); ++i) {
        if (Ptr != CI->getArgOperand(i))
          continue;

        const DxilParameterAnnotation &paramAnnotation =
            funcAnnotation->GetParameterAnnotation(i);
        // OutputPatch and OutputStream will be checked after scalar repl.
        // Here only check out/inout
        if (paramAnnotation.GetParamInputQual() == DxilParamInputQual::Out ||
            paramAnnotation.GetParamInputQual() == DxilParamInputQual::Inout) {
          bReadOnly = false;
          break;
        }
      }

      if (!bReadOnly)
        PropagatePreciseAttributeOnOperand(CI, typeSys, Context, processedSet);
    }
  }
}

static void
PropagatePreciseAttribute(Instruction *I, DxilTypeSystem &typeSys,
                          std::unordered_set<Instruction *> &processedSet) {
  LLVMContext &Context = I->getContext();
  if (AllocaInst *AI = dyn_cast<AllocaInst>(I)) {
    PropagatePreciseAttributeOnPointer(AI, typeSys, Context, processedSet);
  } else if (dyn_cast<CallInst>(I)) {
    // Propagate every argument.
    // TODO: only propagate precise argument.
    for (Value *src : I->operands())
      PropagatePreciseAttributeOnOperand(src, typeSys, Context, processedSet);
  } else if (dyn_cast<FPMathOperator>(I)) {
    // TODO: only propagate precise argument.
    for (Value *src : I->operands())
      PropagatePreciseAttributeOnOperand(src, typeSys, Context, processedSet);
  } else if (LoadInst *ldInst = dyn_cast<LoadInst>(I)) {
    Value *Ptr = ldInst->getPointerOperand();
    PropagatePreciseAttributeOnPointer(Ptr, typeSys, Context, processedSet);
  } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(I))
    PropagatePreciseAttributeOnPointer(GEP, typeSys, Context, processedSet);
  // TODO: support more case which need
}

void DxilPrecisePropagatePass::PropagatePreciseOnFunctionUser(
    Function &F, DxilTypeSystem &typeSys,
    std::unordered_set<Instruction *> &processedSet) {
  LLVMContext &Context = F.getContext();
  for (auto U = F.user_begin(), E = F.user_end(); U != E;) {
    CallInst *CI = cast<CallInst>(*(U++));
    Value *V = CI->getArgOperand(0);
    PropagatePreciseAttributeOnOperand(V, typeSys, Context, processedSet);
    CI->eraseFromParent();
  }
}

ModulePass *llvm::createDxilPrecisePropagatePass() {
  return new DxilPrecisePropagatePass();
}

INITIALIZE_PASS(DxilPrecisePropagatePass, "hlsl-dxil-precise", "DXIL precise attribute propagate", false, false)