SPIRV/Transforms/UnifyAliasedResourcePass.cpp

//===- UnifyAliasedResourcePass.cpp - Pass to Unify Aliased Resources -----===//
//
// 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 file implements a pass that unifies access of multiple aliased resources
// into access of one single resource.
//
//===----------------------------------------------------------------------===//

#include "PassDetail.h"
#include "mlir/Dialect/SPIRV/IR/SPIRVDialect.h"
#include "mlir/Dialect/SPIRV/IR/SPIRVOps.h"
#include "mlir/Dialect/SPIRV/IR/SPIRVTypes.h"
#include "mlir/Dialect/SPIRV/Transforms/Passes.h"
#include "mlir/IR/Builders.h"
#include "mlir/IR/BuiltinAttributes.h"
#include "mlir/IR/BuiltinTypes.h"
#include "mlir/IR/SymbolTable.h"
#include "mlir/Pass/AnalysisManager.h"
#include "mlir/Transforms/DialectConversion.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/Support/Debug.h"
#include <algorithm>

#define DEBUG_TYPE "spirv-unify-aliased-resource"

using namespace mlir;

//===----------------------------------------------------------------------===//
// Utility functions
//===----------------------------------------------------------------------===//

using Descriptor = std::pair<uint32_t, uint32_t>; // (set #, binding #)
using AliasedResourceMap =
    DenseMap<Descriptor, SmallVector<spirv::GlobalVariableOp>>;

/// Collects all aliased resources in the given SPIR-V `moduleOp`.
static AliasedResourceMap collectAliasedResources(spirv::ModuleOp moduleOp) {
  AliasedResourceMap aliasedResoruces;
  moduleOp->walk([&aliasedResoruces](spirv::GlobalVariableOp varOp) {
    if (varOp->getAttrOfType<UnitAttr>("aliased")) {
      Optional<uint32_t> set = varOp.descriptor_set();
      Optional<uint32_t> binding = varOp.binding();
      if (set && binding)
        aliasedResoruces[{*set, *binding}].push_back(varOp);
    }
  });
  return aliasedResoruces;
}

/// Returns the element type if the given `type` is a runtime array resource:
/// `!spv.ptr<!spv.struct<!spv.rtarray<...>>>`. Returns null type otherwise.
static Type getRuntimeArrayElementType(Type type) {
  auto ptrType = type.dyn_cast<spirv::PointerType>();
  if (!ptrType)
    return {};

  auto structType = ptrType.getPointeeType().dyn_cast<spirv::StructType>();
  if (!structType || structType.getNumElements() != 1)
    return {};

  auto rtArrayType =
      structType.getElementType(0).dyn_cast<spirv::RuntimeArrayType>();
  if (!rtArrayType)
    return {};

  return rtArrayType.getElementType();
}

/// Returns true if all `types`, which can either be scalar or vector types,
/// have the same bitwidth base scalar type.
static bool hasSameBitwidthScalarType(ArrayRef<spirv::SPIRVType> types) {
  SmallVector<int64_t> scalarTypes;
  scalarTypes.reserve(types.size());
  for (spirv::SPIRVType type : types) {
    assert(type.isScalarOrVector());
    if (auto vectorType = type.dyn_cast<VectorType>())
      scalarTypes.push_back(
          vectorType.getElementType().getIntOrFloatBitWidth());
    else
      scalarTypes.push_back(type.getIntOrFloatBitWidth());
  }
  return llvm::is_splat(scalarTypes);
}

//===----------------------------------------------------------------------===//
// Analysis
//===----------------------------------------------------------------------===//

namespace {
/// A class for analyzing aliased resources.
///
/// Resources are expected to be spv.GlobalVarible that has a descriptor set and
/// binding number. Such resources are of the type `!spv.ptr<!spv.struct<...>>`
/// per Vulkan requirements.
///
/// Right now, we only support the case that there is a single runtime array
/// inside the struct.
class ResourceAliasAnalysis {
public:
  explicit ResourceAliasAnalysis(Operation *);

  /// Returns true if the given `op` can be rewritten to use a canonical
  /// resource.
  bool shouldUnify(Operation *op) const;

  /// Returns all descriptors and their corresponding aliased resources.
  const AliasedResourceMap &getResourceMap() const { return resourceMap; }

  /// Returns the canonical resource for the given descriptor/variable.
  spirv::GlobalVariableOp
  getCanonicalResource(const Descriptor &descriptor) const;
  spirv::GlobalVariableOp
  getCanonicalResource(spirv::GlobalVariableOp varOp) const;

  /// Returns the element type for the given variable.
  spirv::SPIRVType getElementType(spirv::GlobalVariableOp varOp) const;

private:
  /// Given the descriptor and aliased resources bound to it, analyze whether we
  /// can unify them and record if so.
  void recordIfUnifiable(const Descriptor &descriptor,
                         ArrayRef<spirv::GlobalVariableOp> resources);

  /// Mapping from a descriptor to all aliased resources bound to it.
  AliasedResourceMap resourceMap;

  /// Mapping from a descriptor to the chosen canonical resource.
  DenseMap<Descriptor, spirv::GlobalVariableOp> canonicalResourceMap;

  /// Mapping from an aliased resource to its descriptor.
  DenseMap<spirv::GlobalVariableOp, Descriptor> descriptorMap;

  /// Mapping from an aliased resource to its element (scalar/vector) type.
  DenseMap<spirv::GlobalVariableOp, spirv::SPIRVType> elementTypeMap;
};
} // namespace

ResourceAliasAnalysis::ResourceAliasAnalysis(Operation *root) {
  // Collect all aliased resources first and put them into different sets
  // according to the descriptor.
  AliasedResourceMap aliasedResoruces =
      collectAliasedResources(cast<spirv::ModuleOp>(root));

  // For each resource set, analyze whether we can unify; if so, try to identify
  // a canonical resource, whose element type has the largest bitwidth.
  for (const auto &descriptorResoruce : aliasedResoruces) {
    recordIfUnifiable(descriptorResoruce.first, descriptorResoruce.second);
  }
}

bool ResourceAliasAnalysis::shouldUnify(Operation *op) const {
  if (auto varOp = dyn_cast<spirv::GlobalVariableOp>(op)) {
    auto canonicalOp = getCanonicalResource(varOp);
    return canonicalOp && varOp != canonicalOp;
  }
  if (auto addressOp = dyn_cast<spirv::AddressOfOp>(op)) {
    auto moduleOp = addressOp->getParentOfType<spirv::ModuleOp>();
    auto *varOp = SymbolTable::lookupSymbolIn(moduleOp, addressOp.variable());
    return shouldUnify(varOp);
  }

  if (auto acOp = dyn_cast<spirv::AccessChainOp>(op))
    return shouldUnify(acOp.base_ptr().getDefiningOp());
  if (auto loadOp = dyn_cast<spirv::LoadOp>(op))
    return shouldUnify(loadOp.ptr().getDefiningOp());
  if (auto storeOp = dyn_cast<spirv::StoreOp>(op))
    return shouldUnify(storeOp.ptr().getDefiningOp());

  return false;
}

spirv::GlobalVariableOp ResourceAliasAnalysis::getCanonicalResource(
    const Descriptor &descriptor) const {
  auto varIt = canonicalResourceMap.find(descriptor);
  if (varIt == canonicalResourceMap.end())
    return {};
  return varIt->second;
}

spirv::GlobalVariableOp ResourceAliasAnalysis::getCanonicalResource(
    spirv::GlobalVariableOp varOp) const {
  auto descriptorIt = descriptorMap.find(varOp);
  if (descriptorIt == descriptorMap.end())
    return {};
  return getCanonicalResource(descriptorIt->second);
}

spirv::SPIRVType
ResourceAliasAnalysis::getElementType(spirv::GlobalVariableOp varOp) const {
  auto it = elementTypeMap.find(varOp);
  if (it == elementTypeMap.end())
    return {};
  return it->second;
}

void ResourceAliasAnalysis::recordIfUnifiable(
    const Descriptor &descriptor, ArrayRef<spirv::GlobalVariableOp> resources) {
  // Collect the element types and byte counts for all resources in the
  // current set.
  SmallVector<spirv::SPIRVType> elementTypes;
  SmallVector<int64_t> numBytes;

  for (spirv::GlobalVariableOp resource : resources) {
    Type elementType = getRuntimeArrayElementType(resource.type());
    if (!elementType)
      return; // Unexpected resource variable type.

    auto type = elementType.cast<spirv::SPIRVType>();
    if (!type.isScalarOrVector())
      return; // Unexpected resource element type.

    if (auto vectorType = type.dyn_cast<VectorType>())
      if (vectorType.getNumElements() % 2 != 0)
        return; // Odd-sized vector has special layout requirements.

    Optional<int64_t> count = type.getSizeInBytes();
    if (!count)
      return;

    elementTypes.push_back(type);
    numBytes.push_back(*count);
  }

  // Make sure base scalar types have the same bitwdith, so that we don't need
  // to handle extracting components for now.
  if (!hasSameBitwidthScalarType(elementTypes))
    return;

  // Make sure that the canonical resource's bitwidth is divisible by others.
  // With out this, we cannot properly adjust the index later.
  auto *maxCount = std::max_element(numBytes.begin(), numBytes.end());
  if (llvm::any_of(numBytes, [maxCount](int64_t count) {
        return *maxCount % count != 0;
      }))
    return;

  spirv::GlobalVariableOp canonicalResource =
      resources[std::distance(numBytes.begin(), maxCount)];

  // Update internal data structures for later use.
  resourceMap[descriptor].assign(resources.begin(), resources.end());
  canonicalResourceMap[descriptor] = canonicalResource;
  for (const auto &resource : llvm::enumerate(resources)) {
    descriptorMap[resource.value()] = descriptor;
    elementTypeMap[resource.value()] = elementTypes[resource.index()];
  }
}

//===----------------------------------------------------------------------===//
// Patterns
//===----------------------------------------------------------------------===//

template <typename OpTy>
class ConvertAliasResoruce : public OpConversionPattern<OpTy> {
public:
  ConvertAliasResoruce(const ResourceAliasAnalysis &analysis,
                       MLIRContext *context, PatternBenefit benefit = 1)
      : OpConversionPattern<OpTy>(context, benefit), analysis(analysis) {}

protected:
  const ResourceAliasAnalysis &analysis;
};

struct ConvertVariable : public ConvertAliasResoruce<spirv::GlobalVariableOp> {
  using ConvertAliasResoruce::ConvertAliasResoruce;

  LogicalResult
  matchAndRewrite(spirv::GlobalVariableOp varOp, OpAdaptor adaptor,
                  ConversionPatternRewriter &rewriter) const override {
    // Just remove the aliased resource. Users will be rewritten to use the
    // canonical one.
    rewriter.eraseOp(varOp);
    return success();
  }
};

struct ConvertAddressOf : public ConvertAliasResoruce<spirv::AddressOfOp> {
  using ConvertAliasResoruce::ConvertAliasResoruce;

  LogicalResult
  matchAndRewrite(spirv::AddressOfOp addressOp, OpAdaptor adaptor,
                  ConversionPatternRewriter &rewriter) const override {
    // Rewrite the AddressOf op to get the address of the canoncical resource.
    auto moduleOp = addressOp->getParentOfType<spirv::ModuleOp>();
    auto srcVarOp = cast<spirv::GlobalVariableOp>(
        SymbolTable::lookupSymbolIn(moduleOp, addressOp.variable()));
    auto dstVarOp = analysis.getCanonicalResource(srcVarOp);
    rewriter.replaceOpWithNewOp<spirv::AddressOfOp>(addressOp, dstVarOp);
    return success();
  }
};

struct ConvertAccessChain : public ConvertAliasResoruce<spirv::AccessChainOp> {
  using ConvertAliasResoruce::ConvertAliasResoruce;

  LogicalResult
  matchAndRewrite(spirv::AccessChainOp acOp, OpAdaptor adaptor,
                  ConversionPatternRewriter &rewriter) const override {
    auto addressOp = acOp.base_ptr().getDefiningOp<spirv::AddressOfOp>();
    if (!addressOp)
      return rewriter.notifyMatchFailure(acOp, "base ptr not addressof op");

    auto moduleOp = acOp->getParentOfType<spirv::ModuleOp>();
    auto srcVarOp = cast<spirv::GlobalVariableOp>(
        SymbolTable::lookupSymbolIn(moduleOp, addressOp.variable()));
    auto dstVarOp = analysis.getCanonicalResource(srcVarOp);

    spirv::SPIRVType srcElemType = analysis.getElementType(srcVarOp);
    spirv::SPIRVType dstElemType = analysis.getElementType(dstVarOp);

    if ((srcElemType == dstElemType) ||
        (srcElemType.isIntOrFloat() && dstElemType.isIntOrFloat())) {
      // We have the same bitwidth for source and destination element types.
      // Thie indices keep the same.
      rewriter.replaceOpWithNewOp<spirv::AccessChainOp>(
          acOp, adaptor.base_ptr(), adaptor.indices());
      return success();
    }

    Location loc = acOp.getLoc();
    auto i32Type = rewriter.getI32Type();

    if (srcElemType.isIntOrFloat() && dstElemType.isa<VectorType>()) {
      // The source indices are for a buffer with scalar element types. Rewrite
      // them into a buffer with vector element types. We need to scale the last
      // index for the vector as a whole, then add one level of index for inside
      // the vector.
      int ratio = *dstElemType.getSizeInBytes() / *srcElemType.getSizeInBytes();
      auto ratioValue = rewriter.create<spirv::ConstantOp>(
          loc, i32Type, rewriter.getI32IntegerAttr(ratio));

      auto indices = llvm::to_vector<4>(acOp.indices());
      Value oldIndex = indices.back();
      indices.back() =
          rewriter.create<spirv::SDivOp>(loc, i32Type, oldIndex, ratioValue);
      indices.push_back(
          rewriter.create<spirv::SModOp>(loc, i32Type, oldIndex, ratioValue));

      rewriter.replaceOpWithNewOp<spirv::AccessChainOp>(
          acOp, adaptor.base_ptr(), indices);
      return success();
    }

    return rewriter.notifyMatchFailure(acOp, "unsupported src/dst types");
  }
};

struct ConvertLoad : public ConvertAliasResoruce<spirv::LoadOp> {
  using ConvertAliasResoruce::ConvertAliasResoruce;

  LogicalResult
  matchAndRewrite(spirv::LoadOp loadOp, OpAdaptor adaptor,
                  ConversionPatternRewriter &rewriter) const override {
    auto srcElemType =
        loadOp.ptr().getType().cast<spirv::PointerType>().getPointeeType();
    auto dstElemType =
        adaptor.ptr().getType().cast<spirv::PointerType>().getPointeeType();
    if (!srcElemType.isIntOrFloat() || !dstElemType.isIntOrFloat())
      return rewriter.notifyMatchFailure(loadOp, "not scalar type");

    Location loc = loadOp.getLoc();
    auto newLoadOp = rewriter.create<spirv::LoadOp>(loc, adaptor.ptr());
    if (srcElemType == dstElemType) {
      rewriter.replaceOp(loadOp, newLoadOp->getResults());
    } else {
      auto castOp = rewriter.create<spirv::BitcastOp>(loc, srcElemType,
                                                      newLoadOp.value());
      rewriter.replaceOp(loadOp, castOp->getResults());
    }

    return success();
  }
};

struct ConvertStore : public ConvertAliasResoruce<spirv::StoreOp> {
  using ConvertAliasResoruce::ConvertAliasResoruce;

  LogicalResult
  matchAndRewrite(spirv::StoreOp storeOp, OpAdaptor adaptor,
                  ConversionPatternRewriter &rewriter) const override {
    auto srcElemType =
        storeOp.ptr().getType().cast<spirv::PointerType>().getPointeeType();
    auto dstElemType =
        adaptor.ptr().getType().cast<spirv::PointerType>().getPointeeType();
    if (!srcElemType.isIntOrFloat() || !dstElemType.isIntOrFloat())
      return rewriter.notifyMatchFailure(storeOp, "not scalar type");

    Location loc = storeOp.getLoc();
    Value value = adaptor.value();
    if (srcElemType != dstElemType)
      value = rewriter.create<spirv::BitcastOp>(loc, dstElemType, value);
    rewriter.replaceOpWithNewOp<spirv::StoreOp>(storeOp, adaptor.ptr(), value,
                                                storeOp->getAttrs());
    return success();
  }
};

//===----------------------------------------------------------------------===//
// Pass
//===----------------------------------------------------------------------===//

namespace {
class UnifyAliasedResourcePass final
    : public SPIRVUnifyAliasedResourcePassBase<UnifyAliasedResourcePass> {
public:
  void runOnOperation() override;
};
} // namespace

void UnifyAliasedResourcePass::runOnOperation() {
  spirv::ModuleOp moduleOp = getOperation();
  MLIRContext *context = &getContext();

  // Analyze aliased resources first.
  ResourceAliasAnalysis &analysis = getAnalysis<ResourceAliasAnalysis>();

  ConversionTarget target(*context);
  target.addDynamicallyLegalOp<spirv::GlobalVariableOp, spirv::AddressOfOp,
                               spirv::AccessChainOp, spirv::LoadOp,
                               spirv::StoreOp>(
      [&analysis](Operation *op) { return !analysis.shouldUnify(op); });
  target.addLegalDialect<spirv::SPIRVDialect>();

  // Run patterns to rewrite usages of non-canonical resources.
  RewritePatternSet patterns(context);
  patterns.add<ConvertVariable, ConvertAddressOf, ConvertAccessChain,
               ConvertLoad, ConvertStore>(analysis, context);
  if (failed(applyPartialConversion(moduleOp, target, std::move(patterns))))
    return signalPassFailure();

  // Drop aliased attribute if we only have one single bound resource for a
  // descriptor. We need to re-collect the map here given in the above the
  // conversion is best effort; certain sets may not be converted.
  AliasedResourceMap resourceMap =
      collectAliasedResources(cast<spirv::ModuleOp>(moduleOp));
  for (const auto &dr : resourceMap) {
    const auto &resources = dr.second;
    if (resources.size() == 1)
      resources.front()->removeAttr("aliased");
  }
}

std::unique_ptr<mlir::OperationPass<spirv::ModuleOp>>
spirv::createUnifyAliasedResourcePass() {
  return std::make_unique<UnifyAliasedResourcePass>();
}