HWLegalizeModules.cpp

//===- HWLegalizeModulesPass.cpp - Lower unsupported IR features away -----===//
//
// 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 lowers away features in the SV/Comb/HW dialects that are
// unsupported by some tools (e.g. multidimensional arrays) as specified by
// LoweringOptions.  This pass is run relatively late in the pipeline in
// preparation for emission.  Any passes run after this (e.g. PrettifyVerilog)
// must be aware they cannot introduce new invalid constructs.
//
//===----------------------------------------------------------------------===//

#include "circt/Dialect/Comb/CombOps.h"
#include "circt/Dialect/HW/HWOps.h"
#include "circt/Dialect/HW/HWTypes.h"
#include "circt/Dialect/SV/SVOps.h"
#include "circt/Dialect/SV/SVPasses.h"
#include "circt/Support/LoweringOptions.h"
#include "mlir/IR/Builders.h"
#include "mlir/Pass/Pass.h"

namespace circt {
namespace sv {
#define GEN_PASS_DEF_HWLEGALIZEMODULES
#include "circt/Dialect/SV/SVPasses.h.inc"
} // namespace sv
} // namespace circt

using namespace circt;
//===----------------------------------------------------------------------===//
// HWLegalizeModulesPass
//===----------------------------------------------------------------------===//

namespace {
struct HWLegalizeModulesPass
    : public circt::sv::impl::HWLegalizeModulesBase<HWLegalizeModulesPass> {
  void runOnOperation() override;

private:
  void processPostOrder(Block &block);
  bool tryLoweringPackedArrayOp(Operation &op);
  template <typename ElementType>
  SmallVector<std::pair<Value, Value>>
  createIndexValuePairs(OpBuilder &builder, LocationAttr loc, hw::ArrayType ty,
                        Value array);
  Value lowerLookupToCasez(Operation &op, Value input, Value index,
                           mlir::Type elementType,
                           SmallVector<Value> caseValues);
  bool processUsers(Operation &op, Value value, ArrayRef<Value> mapping);
  std::optional<std::pair<uint64_t, unsigned>>
  tryExtractIndexAndBitWidth(Value value);
  bool tryLoweringClockedAssertLike(Operation &op);

  /// This is the current hw.module being processed.
  hw::HWModuleOp thisHWModule;

  bool anythingChanged;

  /// This tells us what language features we're allowed to use in generated
  /// Verilog.
  LoweringOptions options;

  /// This pass will be run on multiple hw.modules, this keeps track of the
  /// contents of LoweringOptions so we don't have to reparse the
  /// LoweringOptions for every hw.module.
  StringAttr lastParsedOptions;
};
} // end anonymous namespace

bool HWLegalizeModulesPass::tryLoweringPackedArrayOp(Operation &op) {
  return TypeSwitch<Operation *, bool>(&op)
      .Case<hw::AggregateConstantOp>([&](hw::AggregateConstantOp constOp) {
        // Replace individual element uses (if any) with input fields.
        SmallVector<Value> inputs;
        OpBuilder builder(constOp);
        for (auto field : llvm::reverse(constOp.getFields())) {
          if (auto intAttr = dyn_cast<IntegerAttr>(field))
            inputs.push_back(
                hw::ConstantOp::create(builder, constOp.getLoc(), intAttr));
          else
            inputs.push_back(hw::AggregateConstantOp::create(
                builder, constOp.getLoc(), constOp.getType(),
                cast<ArrayAttr>(field)));
        }
        if (!processUsers(op, constOp.getResult(), inputs))
          return false;

        // Remove original op.
        return true;
      })
      .Case<hw::ArrayConcatOp>([&](hw::ArrayConcatOp concatOp) {
        // Redirect individual element uses (if any) to the input arguments.
        SmallVector<Value> values;
        OpBuilder builder(concatOp);
        for (auto array : llvm::reverse(concatOp.getInputs())) {
          auto ty = hw::type_cast<hw::ArrayType>(array.getType());
          const auto indexValues = createIndexValuePairs<hw::ArrayGetOp>(
              builder, concatOp.getLoc(), ty, array);
          for (const auto &[_, value] : indexValues) {
            values.push_back(value);
          }
        }
        if (!processUsers(op, concatOp.getResult(), values))
          return false;

        // Remove original op.
        return true;
      })
      .Case<hw::ArrayCreateOp>([&](hw::ArrayCreateOp createOp) {
        // Replace individual element uses (if any) with input arguments.
        SmallVector<Value> inputs(llvm::reverse(createOp.getInputs()));
        if (!processUsers(op, createOp.getResult(), inputs))
          return false;

        // Remove original op.
        return true;
      })
      .Case<hw::ArrayGetOp>([&](hw::ArrayGetOp getOp) {
        // Skip index ops with constant index.
        auto index = getOp.getIndex();
        if (auto *definingOp = index.getDefiningOp())
          if (isa<hw::ConstantOp>(definingOp))
            return false;

        // Generate case value element lookups.
        auto ty = hw::type_cast<hw::ArrayType>(getOp.getInput().getType());
        OpBuilder builder(getOp);
        auto loc = op.getLoc();
        const auto indexValues = createIndexValuePairs<hw::ArrayGetOp>(
            builder, loc, ty, getOp.getInput());
        SmallVector<Value> caseValues;
        for (const auto &[_, value] : indexValues)
          caseValues.push_back(value);

        // Transform array index op into casez statement.
        auto theWire = lowerLookupToCasez(op, getOp.getInput(), index,
                                          ty.getElementType(), caseValues);

        // Emit the read from the wire, replace uses and clean up.
        builder.setInsertionPoint(getOp);
        auto readWire =
            sv::ReadInOutOp::create(builder, getOp.getLoc(), theWire);
        getOp.getResult().replaceAllUsesWith(readWire);
        return true;
      })
      .Case<sv::ArrayIndexInOutOp>([&](sv::ArrayIndexInOutOp indexOp) {
        // Skip index ops with constant index.
        auto index = indexOp.getIndex();
        if (auto *definingOp = index.getDefiningOp())
          if (isa<hw::ConstantOp>(definingOp))
            return false;

        // Skip index ops with unpacked arrays.
        auto inout = indexOp.getInput().getType();
        if (hw::type_isa<hw::UnpackedArrayType>(inout.getElementType()))
          return false;

        // Generate case value element lookups.
        auto ty = hw::type_cast<hw::ArrayType>(inout.getElementType());
        OpBuilder builder(&op);
        auto loc = op.getLoc();
        const auto indexValues = createIndexValuePairs<sv::ArrayIndexInOutOp>(
            builder, loc, ty, indexOp.getInput());
        SmallVector<Value> caseValues;
        for (const auto &[_, element] : indexValues) {
          auto readElement = sv::ReadInOutOp::create(builder, loc, element);
          caseValues.push_back(readElement);
        }

        // Transform array index op into casez statement.
        auto theWire = lowerLookupToCasez(op, indexOp.getInput(), index,
                                          ty.getElementType(), caseValues);

        // Replace uses and clean up.
        indexOp.getResult().replaceAllUsesWith(theWire);
        return true;
      })
      .Case<sv::PAssignOp>([&](sv::PAssignOp assignOp) {
        // Transform array assignment into individual assignments for each array
        // element.
        auto inout = assignOp.getDest().getType();
        auto ty = hw::type_dyn_cast<hw::ArrayType>(inout.getElementType());
        if (!ty)
          return false;

        OpBuilder builder(assignOp);
        auto loc = op.getLoc();
        const auto indexValues = createIndexValuePairs<hw::ArrayGetOp>(
            builder, loc, ty, assignOp.getSrc());
        for (const auto &[index, srcElement] : indexValues) {
          auto dstElement = sv::ArrayIndexInOutOp::create(
              builder, loc, assignOp.getDest(), index);
          sv::PAssignOp::create(builder, loc, dstElement, srcElement);
        }

        // Remove original assignment.
        return true;
      })
      .Case<sv::RegOp>([&](sv::RegOp regOp) {
        // Transform array reg into individual regs for each array element.
        auto ty = hw::type_dyn_cast<hw::ArrayType>(regOp.getElementType());
        if (!ty)
          return false;

        OpBuilder builder(regOp);
        auto name = StringAttr::get(regOp.getContext(), "name");
        SmallVector<Value> elements;
        for (size_t i = 0, e = ty.getNumElements(); i < e; i++) {
          auto loc = op.getLoc();
          auto element = sv::RegOp::create(builder, loc, ty.getElementType());
          if (auto nameAttr = regOp->getAttrOfType<StringAttr>(name)) {
            element.setNameAttr(
                StringAttr::get(regOp.getContext(), nameAttr.getValue()));
          }
          elements.push_back(element);
        }

        // Fix users to refer to individual element regs.
        if (!processUsers(op, regOp.getResult(), elements))
          return false;

        // Remove original reg.
        return true;
      })
      .Case<comb::MuxOp>([&](comb::MuxOp muxOp) {
        // Transform array mux into individual element muxes.
        auto ty = hw::type_dyn_cast<hw::ArrayType>(muxOp.getType());
        if (!ty)
          return false;

        OpBuilder builder(muxOp);

        auto trueValues = createIndexValuePairs<hw::ArrayGetOp>(
            builder, muxOp.getLoc(), ty, muxOp.getTrueValue());
        auto falseValues = createIndexValuePairs<hw::ArrayGetOp>(
            builder, muxOp.getLoc(), ty, muxOp.getFalseValue());

        SmallVector<Value> muxedValues;

        for (size_t i = 0, e = trueValues.size(); i < e; i++) {
          const auto &[trueIndex, trueValue] = trueValues[i];
          const auto &[falseIndex, falseValue] = falseValues[i];
          muxedValues.push_back(
              comb::MuxOp::create(builder, muxOp.getLoc(), muxOp.getCond(),
                                  trueValue, falseValue, muxOp.getTwoState()));
        }

        if (!processUsers(op, muxOp.getResult(), muxedValues))
          return false;

        // Remove original mux.
        return true;
      })
      .Default([&](auto op) { return false; });
}

template <typename ElementType>
SmallVector<std::pair<Value, Value>>
HWLegalizeModulesPass::createIndexValuePairs(OpBuilder &builder,
                                             LocationAttr loc, hw::ArrayType ty,
                                             Value array) {
  SmallVector<std::pair<Value, Value>> result;
  for (size_t i = 0, e = ty.getNumElements(); i < e; i++) {
    auto index = builder.createOrFold<hw::ConstantOp>(
        loc, APInt(llvm::Log2_64_Ceil(e), i));
    auto element = ElementType::create(builder, loc, array, index);
    result.emplace_back(index, element);
  }
  return result;
}

Value HWLegalizeModulesPass::lowerLookupToCasez(Operation &op, Value input,
                                                Value index,
                                                mlir::Type elementType,
                                                SmallVector<Value> caseValues) {
  // Create the wire for the result of the casez in the
  // hw.module.
  OpBuilder builder(&op);
  auto theWire = sv::RegOp::create(builder, op.getLoc(), elementType,
                                   builder.getStringAttr("casez_tmp"));
  builder.setInsertionPoint(&op);

  auto loc = input.getLoc();
  // A casez is a procedural operation, so if we're in a
  // non-procedural region we need to inject an always_comb
  // block.
  if (!op.getParentOp()->hasTrait<sv::ProceduralRegion>()) {
    auto alwaysComb = sv::AlwaysCombOp::create(builder, loc);
    builder.setInsertionPointToEnd(alwaysComb.getBodyBlock());
  }

  // If we are missing elements in the array (it is non-power of
  // two), then add a default 'X' value.
  if (1ULL << index.getType().getIntOrFloatBitWidth() != caseValues.size()) {
    caseValues.push_back(sv::ConstantXOp::create(builder, op.getLoc(),
                                                 op.getResult(0).getType()));
  }

  APInt caseValue(index.getType().getIntOrFloatBitWidth(), 0);
  auto *context = builder.getContext();

  // Create the casez itself.
  sv::CaseOp::create(
      builder, loc, CaseStmtType::CaseZStmt, index, caseValues.size(),
      [&](size_t caseIdx) -> std::unique_ptr<sv::CasePattern> {
        // Use a default pattern for the last value, even if we
        // are complete. This avoids tools thinking they need to
        // insert a latch due to potentially incomplete case
        // coverage.
        bool isDefault = caseIdx == caseValues.size() - 1;
        Value theValue = caseValues[caseIdx];
        std::unique_ptr<sv::CasePattern> thePattern;

        if (isDefault)
          thePattern = std::make_unique<sv::CaseDefaultPattern>(context);
        else
          thePattern = std::make_unique<sv::CaseBitPattern>(caseValue, context);
        ++caseValue;
        sv::BPAssignOp::create(builder, loc, theWire, theValue);
        return thePattern;
      });

  return theWire;
}

bool HWLegalizeModulesPass::processUsers(Operation &op, Value value,
                                         ArrayRef<Value> mapping) {
  for (auto *user : llvm::make_early_inc_range(value.getUsers())) {
    if (TypeSwitch<Operation *, bool>(user)
            .Case<hw::ArrayGetOp>([&](hw::ArrayGetOp getOp) {
              if (auto indexAndBitWidth =
                      tryExtractIndexAndBitWidth(getOp.getIndex())) {
                getOp.replaceAllUsesWith(mapping[indexAndBitWidth->first]);
                return true;
              }

              return false;
            })
            .Case<sv::ArrayIndexInOutOp>([&](sv::ArrayIndexInOutOp indexOp) {
              if (auto indexAndBitWidth =
                      tryExtractIndexAndBitWidth(indexOp.getIndex())) {
                indexOp.replaceAllUsesWith(mapping[indexAndBitWidth->first]);
                return true;
              }

              return false;
            })
            .Default([](auto op) { return false; })) {
      user->erase();
      continue;
    }

    user->emitError("unsupported packed array expression");
    signalPassFailure();
    return false;
  }

  return true;
}

std::optional<std::pair<uint64_t, unsigned>>
HWLegalizeModulesPass::tryExtractIndexAndBitWidth(Value value) {
  if (auto constantOp = dyn_cast<hw::ConstantOp>(value.getDefiningOp())) {
    auto index = constantOp.getValue();
    return std::make_optional(
        std::make_pair(index.getZExtValue(), index.getBitWidth()));
  }
  return std::nullopt;
}

namespace {
template <typename Op>
bool tryLoweringClockedAssertLike(Op &op) {
  auto event = op.getEvent();
  if (!event.has_value())
    return false;

  OpBuilder builder(op);

  sv::AlwaysOp::create(builder, op->getLoc(), *event, op.getClock(), [&] {
    Op::create(builder, op.getLoc(), op.getProperty(), op.getDisable(),
               op.getLabelAttr());
  });
  return true;
}
} // namespace

bool HWLegalizeModulesPass::tryLoweringClockedAssertLike(Operation &op) {
  return TypeSwitch<Operation *, bool>(&op)
      .Case<sv::AssertPropertyOp>(
          ::tryLoweringClockedAssertLike<sv::AssertPropertyOp>)
      .Case<sv::AssumePropertyOp>(
          ::tryLoweringClockedAssertLike<sv::AssumePropertyOp>)
      .Case<sv::CoverPropertyOp>(
          ::tryLoweringClockedAssertLike<sv::CoverPropertyOp>)
      .Default([&](auto op) { return false; });
}

void HWLegalizeModulesPass::processPostOrder(Block &body) {
  if (body.empty())
    return;

  // Walk the block bottom-up, processing the region tree inside out.
  Block::iterator it = std::prev(body.end());
  while (it != body.end()) {
    auto &op = *it;

    // Advance the iterator, using the end iterator as a sentinel that we're at
    // the top of the block.
    if (it == body.begin())
      it = body.end();
    else
      --it;

    if (op.getNumRegions()) {
      for (auto &region : op.getRegions())
        for (auto &regionBlock : region.getBlocks())
          processPostOrder(regionBlock);
    }

    if (options.disallowPackedArrays) {
      // Try supported packed array op lowering.
      if (tryLoweringPackedArrayOp(op)) {
        it = --Block::iterator(op);
        op.erase();
        anythingChanged = true;
        continue;
      }

      // Otherwise, if the IR produces a packed array and we aren't allowing
      // multi-dimensional arrays, reject the IR as invalid.
      for (auto value : op.getResults()) {
        if (isa<hw::ArrayType>(value.getType())) {
          op.emitError("unsupported packed array expression");
          signalPassFailure();
        }
      }
    }

    if (options.disallowClockedAssertions) {
      if (tryLoweringClockedAssertLike(op)) {
        op.erase();
        anythingChanged = true;
        continue;
      }
    }
  }
}

void HWLegalizeModulesPass::runOnOperation() {
  thisHWModule = getOperation();

  // Parse the lowering options if necessary.
  auto optionsAttr = LoweringOptions::getAttributeFrom(
      cast<ModuleOp>(thisHWModule->getParentOp()));
  if (optionsAttr != lastParsedOptions) {
    if (optionsAttr)
      options = LoweringOptions(optionsAttr.getValue(), [&](Twine error) {
        thisHWModule.emitError(error);
      });
    else
      options = LoweringOptions();
    lastParsedOptions = optionsAttr;
  }

  // Keeps track if anything changed during this pass, used to determine if
  // the analyses were preserved.
  anythingChanged = false;

  // Walk the operations in post-order, transforming any that are interesting.
  processPostOrder(*thisHWModule.getBodyBlock());

  // If we did not change anything in the IR mark all analysis as preserved.
  if (!anythingChanged)
    markAllAnalysesPreserved();
}