Statements.cpp

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//===- Statements.cpp - Slang statement conversion ------------------------===//
//
// 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
//
//===----------------------------------------------------------------------===//
 
#include "ImportVerilogInternals.h"
#include "circt/Dialect/Moore/MooreOps.h"
#include "circt/Dialect/Moore/MooreTypes.h"
#include "mlir/Dialect/Func/IR/FuncOps.h"
#include "mlir/IR/Builders.h"
#include "mlir/IR/Diagnostics.h"
#include "slang/ast/Compilation.h"
#include "slang/ast/SemanticFacts.h"
#include "slang/ast/Statement.h"
#include "slang/ast/SystemSubroutine.h"
#include "slang/ast/expressions/MiscExpressions.h"
#include "slang/ast/symbols/CompilationUnitSymbols.h"
#include "slang/ast/symbols/InstanceSymbols.h"
#include "llvm/ADT/ScopeExit.h"
#include "llvm/Support/raw_ostream.h"
 
using namespace mlir;
using namespace circt;
using namespace ImportVerilog;
 
/// Build the message printed by the `$printtimescale` system task. If a module
/// instance or `$unit` is passed as argument, report that scope's time scale;
/// otherwise report the time scale of the current scope.
static std::string buildPrintTimeScaleMessage(
    Context &context, std::span<const slang::ast::Expression *const> args) {
  auto timeScale = context.timeScale;
  std::string target;
 
  if (!args.empty()) {
    if (auto *expr = args[0]->as_if<slang::ast::ArbitrarySymbolExpression>()) {
      const auto *symbol = expr->symbol.get();
      if (auto *instance = symbol->as_if<slang::ast::InstanceSymbol>()) {
        timeScale = instance->body.getTimeScale().value_or(timeScale);
        target = instance->getHierarchicalPath();
      } else if (auto *unit =
                     symbol->as_if<slang::ast::CompilationUnitSymbol>()) {
        timeScale = unit->getTimeScale().value_or(timeScale);
        target = "$unit";
      } else if (symbol->kind == slang::ast::SymbolKind::Root) {
        target = "$root";
      }
    }
  }
 
  std::string out;
  llvm::raw_string_ostream os(out);
  os << "Time scale";
  if (!target.empty())
    os << " of " << target;
  os << " is " << timeScale.base.toString() << " / "
     << timeScale.precision.toString() << "\n";
  return out;
}
 
static std::array<Value, 4> getDefaultTimeFormatValues(OpBuilder &builder,
                                                       Location loc,
                                                       MLIRContext *context) {
  auto i32Ty = moore::IntType::getInt(context, 32);
 
  auto unit = moore::ConstantOp::create(builder, loc, i32Ty, -15);
  auto precision = moore::ConstantOp::create(builder, loc, i32Ty, 0);
  auto emptyInt = moore::ConstantStringOp::create(
      builder, loc, moore::IntType::getInt(context, 0), "");
  auto suffix = moore::IntToStringOp::create(builder, loc, emptyInt);
  auto minWidth = moore::ConstantOp::create(builder, loc, i32Ty, 20);
 
  return {unit, precision, suffix, minWidth};
}
 
// Get the runtime size of a dynamically-sized array at the given level of a
// foreach loop.
static FailureOr<Value>
getRuntimeSizeAtLevel(Context &context, Location loc,
                      const slang::ast::ForeachLoopStatement &stmt,
                      uint32_t level, const moore::IntType &idxType) {
  auto &builder = context.builder;
  const auto &loopDim = stmt.loopDims[level];
 
  // Get array at the current level
  Value array = context.convertRvalueExpression(stmt.arrayRef);
  for (uint32_t i = 0; i < level; ++i) {
    const auto &dim = stmt.loopDims[i];
    const auto &loopVar = dim.loopVar;
    if (!dim.loopVar)
      mlir::emitError(loc, "unsupported foreach with missing loop variable");
 
    auto nestedType =
        llvm::TypeSwitch<Type, Type>(array.getType())
            .Case<moore::OpenUnpackedArrayType, moore::UnpackedArrayType,
                  moore::ArrayType, moore::OpenArrayType, moore::QueueType,
                  moore::AssocArrayType>(
                [](auto ty) { return ty.getElementType(); })
            .Default([](Type) { return Type(); });
 
    auto curIdx = moore::ReadOp::create(builder, loc,
                                        context.valueSymbols.lookup(loopVar));
    if (dim.range.has_value()) {
      Value offset = getSelectIndex(context, loc, curIdx, dim.range.value());
      array =
          moore::DynExtractOp::create(builder, loc, nestedType, array, offset);
    } else {
      array =
          moore::DynExtractOp::create(builder, loc, nestedType, array, curIdx);
    }
  }
 
  Value size;
  if (loopDim.loopVar->arrayType.isQueue()) {
    size = moore::QueueSizeBIOp::create(builder, loc, array);
  } else if (loopDim.loopVar->arrayType.getCanonicalType().kind ==
             slang::ast::SymbolKind::DynamicArrayType) {
    size = moore::OpenUArraySizeOp::create(builder, loc, array);
  } else {
    // TODO: Associative arrays cannot be iterated on using an induction
    // variable. Supporting them requires rewriting `recursiveForeach` to use
    // the correct iterator type. For now, we just emit an error.
    mlir::emitError(loc, "unsupported foreach loop on type: ")
        << loopDim.loopVar->arrayType.toString();
    return failure();
  }
 
  auto one = moore::ConstantOp::create(builder, loc, idxType, 1);
  auto sizeMinusOne = moore::SubOp::create(builder, loc, size, one).getResult();
  return sizeMinusOne;
}
 
// NOLINTBEGIN(misc-no-recursion)
namespace {
struct StmtVisitor {
  Context &context;
  Location loc;
  OpBuilder &builder;
 
  StmtVisitor(Context &context, Location loc)
      : context(context), loc(loc), builder(context.builder) {}
 
  bool isTerminated() const { return !builder.getInsertionBlock(); }
  void setTerminated() { builder.clearInsertionPoint(); }
 
  Block &createBlock() {
    assert(builder.getInsertionBlock());
    auto block = std::make_unique<Block>();
    block->insertAfter(builder.getInsertionBlock());
    return *block.release();
  }
 
  LogicalResult recursiveForeach(const slang::ast::ForeachLoopStatement &stmt,
                                 uint32_t level) {
    // find current dimension we are operating on.
    const auto &loopDim = stmt.loopDims[level];
    auto &exitBlock = createBlock();
    auto &stepBlock = createBlock();
    auto &bodyBlock = createBlock();
    auto &checkBlock = createBlock();
 
    // Push the blocks onto the loop stack such that we can continue and break.
    context.loopStack.push_back({&stepBlock, &exitBlock});
    llvm::scope_exit done([&] { context.loopStack.pop_back(); });
 
    // Get the loop variable's type
    const auto &iter = loopDim.loopVar;
    auto idxType = context.convertType(*iter->getDeclaredType());
    if (!idxType)
      return failure();
    auto intIdxType = cast<moore::IntType>(idxType);
 
    // Get the loop's lower bound
    Value initial =
        loopDim.range.has_value()
            ? moore::ConstantOp::create(builder, loc, intIdxType,
                                        loopDim.range->lower())
            : moore::ConstantOp::create(builder, loc, intIdxType, 0);
 
    // Create loop variable in this dimension
    Value varOp = moore::VariableOp::create(
        builder, loc, moore::RefType::get(cast<moore::UnpackedType>(idxType)),
        builder.getStringAttr(iter->name), initial);
    context.valueSymbols.insertIntoScope(context.valueSymbols.getCurScope(),
                                         iter, varOp);
 
    cf::BranchOp::create(builder, loc, &checkBlock);
    builder.setInsertionPointToEnd(&checkBlock);
 
    // When the loop variable is greater than the upper bound, goto exit
    auto upperBound =
        loopDim.range.has_value()
            ? moore::ConstantOp::create(builder, loc, intIdxType,
                                        loopDim.range->upper())
            : getRuntimeSizeAtLevel(context, loc, stmt, level, intIdxType)
                  .value_or(Value());
    if (!upperBound)
      return failure();
 
    auto var = moore::ReadOp::create(builder, loc, varOp);
    Value cond = moore::SleOp::create(builder, loc, var, upperBound);
    if (!cond)
      return failure();
    cond = builder.createOrFold<moore::BoolCastOp>(loc, cond);
    if (auto ty = dyn_cast<moore::IntType>(cond.getType());
        ty && ty.getDomain() == Domain::FourValued) {
      cond = moore::LogicToIntOp::create(builder, loc, cond);
    }
    cond = moore::ToBuiltinIntOp::create(builder, loc, cond);
    cf::CondBranchOp::create(builder, loc, cond, &bodyBlock, &exitBlock);
 
    builder.setInsertionPointToEnd(&bodyBlock);
 
    // find next dimension in this foreach statement, it finded then recuersive
    // resolve, else perform body statement
    bool hasNext = false;
    for (uint32_t nextLevel = level + 1; nextLevel < stmt.loopDims.size();
         nextLevel++) {
      if (stmt.loopDims[nextLevel].loopVar) {
        if (failed(recursiveForeach(stmt, nextLevel)))
          return failure();
        hasNext = true;
        break;
      }
    }
 
    if (!hasNext) {
      if (failed(context.convertStatement(stmt.body)))
        return failure();
    }
    if (!isTerminated())
      cf::BranchOp::create(builder, loc, &stepBlock);
 
    builder.setInsertionPointToEnd(&stepBlock);
 
    // add one to loop variable
    var = moore::ReadOp::create(builder, loc, varOp);
    auto one = moore::ConstantOp::create(builder, loc, intIdxType, 1);
    auto postValue = moore::AddOp::create(builder, loc, var, one).getResult();
    moore::BlockingAssignOp::create(builder, loc, varOp, postValue);
    cf::BranchOp::create(builder, loc, &checkBlock);
 
    if (exitBlock.hasNoPredecessors()) {
      exitBlock.erase();
      setTerminated();
    } else {
      builder.setInsertionPointToEnd(&exitBlock);
    }
    return success();
  }
 
  // Skip empty statements (stray semicolons).
  LogicalResult visit(const slang::ast::EmptyStatement &) { return success(); }
 
  // Convert every statement in a statement list. The Verilog syntax follows a
  // similar philosophy as C/C++, where things like `if` and `for` accept a
  // single statement as body. But then a `{...}` block is a valid statement,
  // which allows for the `if {...}` syntax. In Verilog, things like `final`
  // accept a single body statement, but that can be a `begin ... end` block,
  // which in turn has a single body statement, which then commonly is a list of
  // statements.
  LogicalResult visit(const slang::ast::StatementList &stmts) {
    for (auto *stmt : stmts.list) {
      if (isTerminated()) {
        auto loc = context.convertLocation(stmt->sourceRange);
        mlir::emitWarning(loc, "unreachable code");
        break;
      }
      if (failed(context.convertStatement(*stmt)))
        return failure();
    }
    return success();
  }
 
  // Process slang BlockStatements. These comprise all standard `begin ... end`
  // blocks as well as `fork ... join` constructs. Standard blocks can have
  // their contents extracted directly, however fork-join blocks require special
  // handling.
  LogicalResult visit(const slang::ast::BlockStatement &stmt) {
    moore::JoinKind kind;
    switch (stmt.blockKind) {
    case slang::ast::StatementBlockKind::Sequential:
      // Inline standard `begin ... end` blocks into the parent.
      return context.convertStatement(stmt.body);
    case slang::ast::StatementBlockKind::JoinAll:
      kind = moore::JoinKind::Join;
      break;
    case slang::ast::StatementBlockKind::JoinAny:
      kind = moore::JoinKind::JoinAny;
      break;
    case slang::ast::StatementBlockKind::JoinNone:
      kind = moore::JoinKind::JoinNone;
      break;
    }
 
    // Slang stores all threads of a fork-join block inside a `StatementList`.
    // This cannot be visited normally due to the need to make each statement a
    // separate thread so must be converted here. When only a single statement
    // is present, Slang does not create a `StatementList`.
    //
    // Declarations inside a fork block are block items, not separate forked
    // processes. Slang stores them in the same `StatementList` as the forked
    // statements, so convert them in place before creating the fork regions
    // (their values must dominate all threads) and collect the remaining
    // statements as the actual threads.
    SmallVector<const slang::ast::Statement *> items;
    if (auto *threadList = stmt.body.as_if<slang::ast::StatementList>())
      items.append(threadList->list.begin(), threadList->list.end());
    else
      items.push_back(&stmt.body);
 
    SmallVector<const slang::ast::Statement *> threads;
    for (auto *item : items) {
      if (item->as_if<slang::ast::VariableDeclStatement>()) {
        if (failed(context.convertStatement(*item)))
          return failure();
        continue;
      }
      threads.push_back(item);
    }
    // If the fork contained only declarations, there are no threads to spawn
    // and the fork degenerates to the declarations themselves. Genuinely
    // empty forks keep producing an empty fork op.
    if (threads.empty() && !items.empty())
      return success();
 
    auto forkOp = moore::ForkJoinOp::create(builder, loc, kind, threads.size());
    OpBuilder::InsertionGuard guard(builder);
 
    for (auto [i, thread] : llvm::enumerate(threads)) {
      auto &tBlock = forkOp->getRegion(i).emplaceBlock();
      builder.setInsertionPointToStart(&tBlock);
      // Populate thread operator with thread body and finish with a thread
      // terminator.
      if (failed(context.convertStatement(*thread)))
        return failure();
      moore::CompleteOp::create(builder, loc);
    }
    return success();
  }
 
  // Handle expression statements.
  LogicalResult visit(const slang::ast::ExpressionStatement &stmt) {
    // Special handling for calls to system tasks that return no result value.
    if (const auto *call = stmt.expr.as_if<slang::ast::CallExpression>()) {
      if (const auto *info =
              std::get_if<slang::ast::CallExpression::SystemCallInfo>(
                  &call->subroutine)) {
        auto handled = visitSystemCall(stmt, *call, *info);
        if (failed(handled))
          return failure();
        if (handled == true)
          return success();
      }
    }
 
    auto value = context.convertRvalueExpression(stmt.expr);
    if (!value)
      return failure();
 
    // Expressions like calls to void functions return a dummy value that has no
    // uses. If the returned value is trivially dead, remove it.
    if (auto *defOp = value.getDefiningOp())
      if (isOpTriviallyDead(defOp))
        defOp->erase();
 
    return success();
  }
 
  // Handle variable declarations.
  LogicalResult visit(const slang::ast::VariableDeclStatement &stmt) {
    const auto &var = stmt.symbol;
    auto type = context.convertType(*var.getDeclaredType());
    if (!type)
      return failure();
 
    Value initial;
    if (const auto *init = var.getInitializer()) {
      initial = context.convertRvalueExpression(*init, type);
      if (!initial)
        return failure();
    }
 
    // Collect local temporary variables.
    auto varOp = moore::VariableOp::create(
        builder, loc, moore::RefType::get(cast<moore::UnpackedType>(type)),
        builder.getStringAttr(var.name), initial);
    context.valueSymbols.insertIntoScope(context.valueSymbols.getCurScope(),
                                         &var, varOp);
    const auto &canonTy = var.getType().getCanonicalType();
    if (const auto *vi = canonTy.as_if<slang::ast::VirtualInterfaceType>())
      if (failed(context.registerVirtualInterfaceMembers(var, *vi, loc)))
        return failure();
    return success();
  }
 
  // Handle if statements.
  LogicalResult visit(const slang::ast::ConditionalStatement &stmt) {
    // Generate the condition. There may be multiple conditions linked with the
    // `&&&` operator.
    Value allConds;
    for (const auto &condition : stmt.conditions) {
      if (condition.pattern)
        return mlir::emitError(loc,
                               "match patterns in if conditions not supported");
      auto cond = context.convertRvalueExpression(*condition.expr);
      if (!cond)
        return failure();
      cond = builder.createOrFold<moore::BoolCastOp>(loc, cond);
      if (allConds)
        allConds = moore::AndOp::create(builder, loc, allConds, cond);
      else
        allConds = cond;
    }
    assert(allConds && "slang guarantees at least one condition");
    if (auto ty = dyn_cast<moore::IntType>(allConds.getType());
        ty && ty.getDomain() == Domain::FourValued) {
      allConds = moore::LogicToIntOp::create(builder, loc, allConds);
    }
    allConds = moore::ToBuiltinIntOp::create(builder, loc, allConds);
 
    // Create the blocks for the true and false branches, and the exit block.
    Block &exitBlock = createBlock();
    Block *falseBlock = stmt.ifFalse ? &createBlock() : nullptr;
    Block &trueBlock = createBlock();
    cf::CondBranchOp::create(builder, loc, allConds, &trueBlock,
                             falseBlock ? falseBlock : &exitBlock);
 
    // Generate the true branch.
    builder.setInsertionPointToEnd(&trueBlock);
    if (failed(context.convertStatement(stmt.ifTrue)))
      return failure();
    if (!isTerminated())
      cf::BranchOp::create(builder, loc, &exitBlock);
 
    // Generate the false branch if present.
    if (stmt.ifFalse) {
      builder.setInsertionPointToEnd(falseBlock);
      if (failed(context.convertStatement(*stmt.ifFalse)))
        return failure();
      if (!isTerminated())
        cf::BranchOp::create(builder, loc, &exitBlock);
    }
 
    // If control never reaches the exit block, remove it and mark control flow
    // as terminated. Otherwise we continue inserting ops in the exit block.
    if (exitBlock.hasNoPredecessors()) {
      exitBlock.erase();
      setTerminated();
    } else {
      builder.setInsertionPointToEnd(&exitBlock);
    }
    return success();
  }
 
  /// Handle case statements.
  LogicalResult visit(const slang::ast::CaseStatement &caseStmt) {
    using slang::ast::AttributeSymbol;
    using slang::ast::CaseStatementCondition;
    if (auto *caseType =
            caseStmt.expr.as_if<slang::ast::TypeReferenceExpression>()) {
      if (caseStmt.condition != CaseStatementCondition::Normal)
        return mlir::emitError(loc,
                               "unsupported type reference case condition");
 
      const slang::ast::Statement *matchedStmt = nullptr;
      for (const auto &item : caseStmt.items) {
        for (const auto *expr : item.expressions) {
          auto *itemType = expr->as_if<slang::ast::TypeReferenceExpression>();
          if (!itemType)
            return mlir::emitError(
                context.convertLocation(expr->sourceRange),
                "unsupported non-type item in type reference case statement");
          if (itemType->targetType.isMatching(caseType->targetType)) {
            matchedStmt = item.stmt;
            break;
          }
        }
        if (matchedStmt)
          break;
      }
 
      if (matchedStmt)
        return context.convertStatement(*matchedStmt);
      if (caseStmt.defaultCase)
        return context.convertStatement(*caseStmt.defaultCase);
      return success();
    }
 
    auto caseExpr = context.convertRvalueExpression(caseStmt.expr);
    if (!caseExpr)
      return failure();
 
    // Check each case individually. This currently ignores the `unique`,
    // `unique0`, and `priority` modifiers which would allow for additional
    // optimizations.
    auto &exitBlock = createBlock();
    Block *lastMatchBlock = nullptr;
    SmallVector<moore::FVIntegerAttr> itemConsts;
 
    for (const auto &item : caseStmt.items) {
      // Create the block that will contain the main body of the expression.
      // This is where any of the comparisons will branch to if they match.
      auto &matchBlock = createBlock();
      lastMatchBlock = &matchBlock;
 
      // The SV standard requires expressions to be checked in the order
      // specified by the user, and for the evaluation to stop as soon as the
      // first matching expression is encountered.
      for (const auto *expr : item.expressions) {
        Value cond;
        auto itemLoc = loc;
 
        if (caseStmt.condition == CaseStatementCondition::Inside) {
          // ConvertInsideCheck will check insideLhs whether it is empty or not.
          cond = context.convertInsideCheck(
              context.convertToSimpleBitVector(caseExpr), itemLoc, *expr);
          if (!cond)
            return failure();
        } else {
          auto value = context.convertRvalueExpression(*expr);
          if (!value)
            return failure();
          itemLoc = value.getLoc();
 
          // Take note if the expression is a constant.
          auto maybeConst = value;
          while (isa_and_nonnull<moore::IntToLogicOp, moore::LogicToIntOp>(
              maybeConst.getDefiningOp()))
            maybeConst = maybeConst.getDefiningOp()->getOperand(0);
          if (auto defOp = maybeConst.getDefiningOp<moore::ConstantOp>())
            itemConsts.push_back(defOp.getValueAttr());
 
          // Generate the appropriate equality operator. A case statement with
          // real operands uses ordinary equality (`==`) per IEEE 1800 § 11.4.5,
          // not case-equality; wildcard case kinds on reals are illegal SV.
          switch (caseStmt.condition) {
          case CaseStatementCondition::Normal:
            if (isa<moore::RealType>(caseExpr.getType()))
              cond = moore::EqRealOp::create(builder, itemLoc, caseExpr, value);
            else
              cond = moore::CaseEqOp::create(builder, itemLoc, caseExpr, value);
            break;
          case CaseStatementCondition::WildcardXOrZ:
            cond = moore::CaseXZEqOp::create(builder, itemLoc, caseExpr, value);
            break;
          case CaseStatementCondition::WildcardJustZ:
            cond = moore::CaseZEqOp::create(builder, itemLoc, caseExpr, value);
            break;
          case CaseStatementCondition::Inside:
            llvm_unreachable("Inside condition has been handled already");
            break;
          }
        }
 
        if (auto ty = dyn_cast<moore::IntType>(cond.getType());
            ty && ty.getDomain() == Domain::FourValued) {
          cond = moore::LogicToIntOp::create(builder, loc, cond);
        }
        cond = moore::ToBuiltinIntOp::create(builder, loc, cond);
 
        // If the condition matches, branch to the match block. Otherwise
        // continue checking the next expression in a new block.
        auto &nextBlock = createBlock();
        mlir::cf::CondBranchOp::create(builder, itemLoc, cond, &matchBlock,
                                       &nextBlock);
        builder.setInsertionPointToEnd(&nextBlock);
      }
 
      // The current block is the fall-through after all conditions have been
      // checked and nothing matched. Move the match block up before this point
      // to make the IR easier to read.
      matchBlock.moveBefore(builder.getInsertionBlock());
 
      // Generate the code for this item's statement in the match block.
      OpBuilder::InsertionGuard guard(builder);
      builder.setInsertionPointToEnd(&matchBlock);
      if (failed(context.convertStatement(*item.stmt)))
        return failure();
      if (!isTerminated()) {
        auto loc = context.convertLocation(item.stmt->sourceRange);
        mlir::cf::BranchOp::create(builder, loc, &exitBlock);
      }
    }
 
    const auto caseStmtAttrs = context.compilation.getAttributes(caseStmt);
    const bool hasFullCaseAttr =
        llvm::find_if(caseStmtAttrs, [](const AttributeSymbol *attr) {
          return attr->name == "full_case";
        }) != caseStmtAttrs.end();
 
    // Check if the case statement looks exhaustive assuming two-state values.
    // We use this information to work around a common bug in input Verilog
    // where a case statement enumerates all possible two-state values of the
    // case expression, but forgets to deal with cases involving X and Z bits in
    // the input.
    //
    // Once the core dialects start supporting four-state values we may want to
    // tuck this behind an import option that is on by default, since it does
    // not preserve semantics.
    auto twoStateExhaustive = false;
    if (auto intType = dyn_cast<moore::IntType>(caseExpr.getType());
        intType && intType.getWidth() < 32 &&
        itemConsts.size() == (1 << intType.getWidth())) {
      // Sort the constants by value.
      llvm::sort(itemConsts, [](auto a, auto b) {
        return a.getValue().getRawValue().ult(b.getValue().getRawValue());
      });
 
      // Ensure that every possible value of the case expression is present. Do
      // this by starting at 0 and iterating over all sorted items. Each item
      // must be the previous item + 1. At the end, the addition must exactly
      // overflow and take us back to zero.
      auto nextValue = FVInt::getZero(intType.getWidth());
      for (auto value : itemConsts) {
        if (value.getValue() != nextValue)
          break;
        nextValue += 1;
      }
      twoStateExhaustive = nextValue.isZero();
    }
 
    // If the case statement is exhaustive assuming two-state values, don't
    // generate the default case. Instead, branch to the last match block. This
    // will essentially make the last case item the "default".
    //
    // Alternatively, if the case statement has an (* full_case *) attribute
    // but no default case, it indicates that the developer has intentionally
    // covered all known possible values. Hence, the last match block is
    // treated as the implicit "default" case.
    if ((twoStateExhaustive || (hasFullCaseAttr && !caseStmt.defaultCase)) &&
        lastMatchBlock &&
        caseStmt.condition == CaseStatementCondition::Normal) {
      mlir::cf::BranchOp::create(builder, loc, lastMatchBlock);
    } else {
      // Generate the default case if present.
      if (caseStmt.defaultCase)
        if (failed(context.convertStatement(*caseStmt.defaultCase)))
          return failure();
      if (!isTerminated())
        mlir::cf::BranchOp::create(builder, loc, &exitBlock);
    }
 
    // If control never reaches the exit block, remove it and mark control flow
    // as terminated. Otherwise we continue inserting ops in the exit block.
    if (exitBlock.hasNoPredecessors()) {
      exitBlock.erase();
      setTerminated();
    } else {
      builder.setInsertionPointToEnd(&exitBlock);
    }
    return success();
  }
 
  // Handle `for` loops.
  LogicalResult visit(const slang::ast::ForLoopStatement &stmt) {
    // Generate the initializers.
    for (auto *initExpr : stmt.initializers)
      if (!context.convertRvalueExpression(*initExpr))
        return failure();
 
    // Create the blocks for the loop condition, body, step, and exit.
    auto &exitBlock = createBlock();
    auto &stepBlock = createBlock();
    auto &bodyBlock = createBlock();
    auto &checkBlock = createBlock();
    cf::BranchOp::create(builder, loc, &checkBlock);
 
    // Push the blocks onto the loop stack such that we can continue and break.
    context.loopStack.push_back({&stepBlock, &exitBlock});
    llvm::scope_exit done([&] { context.loopStack.pop_back(); });
 
    // Generate the loop condition check.
    builder.setInsertionPointToEnd(&checkBlock);
    auto cond = context.convertRvalueExpression(*stmt.stopExpr);
    if (!cond)
      return failure();
    cond = builder.createOrFold<moore::BoolCastOp>(loc, cond);
    if (auto ty = dyn_cast<moore::IntType>(cond.getType());
        ty && ty.getDomain() == Domain::FourValued) {
      cond = moore::LogicToIntOp::create(builder, loc, cond);
    }
    cond = moore::ToBuiltinIntOp::create(builder, loc, cond);
    cf::CondBranchOp::create(builder, loc, cond, &bodyBlock, &exitBlock);
 
    // Generate the loop body.
    builder.setInsertionPointToEnd(&bodyBlock);
    if (failed(context.convertStatement(stmt.body)))
      return failure();
    if (!isTerminated())
      cf::BranchOp::create(builder, loc, &stepBlock);
 
    // Generate the step expressions.
    builder.setInsertionPointToEnd(&stepBlock);
    for (auto *stepExpr : stmt.steps)
      if (!context.convertRvalueExpression(*stepExpr))
        return failure();
    if (!isTerminated())
      cf::BranchOp::create(builder, loc, &checkBlock);
 
    // If control never reaches the exit block, remove it and mark control flow
    // as terminated. Otherwise we continue inserting ops in the exit block.
    if (exitBlock.hasNoPredecessors()) {
      exitBlock.erase();
      setTerminated();
    } else {
      builder.setInsertionPointToEnd(&exitBlock);
    }
    return success();
  }
 
  LogicalResult visit(const slang::ast::ForeachLoopStatement &stmt) {
    for (uint32_t level = 0; level < stmt.loopDims.size(); level++) {
      if (stmt.loopDims[level].loopVar)
        return recursiveForeach(stmt, level);
    }
    return success();
  }
 
  // Handle `repeat` loops.
  LogicalResult visit(const slang::ast::RepeatLoopStatement &stmt) {
    auto intType = moore::IntType::getInt(context.getContext(), 32);
    auto count = context.convertRvalueExpression(stmt.count, intType);
    if (!count)
      return failure();
 
    // Create the blocks for the loop condition, body, step, and exit.
    auto &exitBlock = createBlock();
    auto &stepBlock = createBlock();
    auto &bodyBlock = createBlock();
    auto &checkBlock = createBlock();
    auto currentCount = checkBlock.addArgument(count.getType(), count.getLoc());
    cf::BranchOp::create(builder, loc, &checkBlock, count);
 
    // Push the blocks onto the loop stack such that we can continue and break.
    context.loopStack.push_back({&stepBlock, &exitBlock});
    llvm::scope_exit done([&] { context.loopStack.pop_back(); });
 
    // Generate the loop condition check.
    builder.setInsertionPointToEnd(&checkBlock);
    auto cond = builder.createOrFold<moore::BoolCastOp>(loc, currentCount);
    if (auto ty = dyn_cast<moore::IntType>(cond.getType());
        ty && ty.getDomain() == Domain::FourValued) {
      cond = moore::LogicToIntOp::create(builder, loc, cond);
    }
    cond = moore::ToBuiltinIntOp::create(builder, loc, cond);
    cf::CondBranchOp::create(builder, loc, cond, &bodyBlock, &exitBlock);
 
    // Generate the loop body.
    builder.setInsertionPointToEnd(&bodyBlock);
    if (failed(context.convertStatement(stmt.body)))
      return failure();
    if (!isTerminated())
      cf::BranchOp::create(builder, loc, &stepBlock);
 
    // Decrement the current count and branch back to the check block.
    builder.setInsertionPointToEnd(&stepBlock);
    auto one = moore::ConstantOp::create(
        builder, count.getLoc(), cast<moore::IntType>(count.getType()), 1);
    Value nextCount =
        moore::SubOp::create(builder, count.getLoc(), currentCount, one);
    cf::BranchOp::create(builder, loc, &checkBlock, nextCount);
 
    // If control never reaches the exit block, remove it and mark control flow
    // as terminated. Otherwise we continue inserting ops in the exit block.
    if (exitBlock.hasNoPredecessors()) {
      exitBlock.erase();
      setTerminated();
    } else {
      builder.setInsertionPointToEnd(&exitBlock);
    }
    return success();
  }
 
  // Handle `while` and `do-while` loops.
  LogicalResult createWhileLoop(const slang::ast::Expression &condExpr,
                                const slang::ast::Statement &bodyStmt,
                                bool atLeastOnce) {
    // Create the blocks for the loop condition, body, and exit.
    auto &exitBlock = createBlock();
    auto &bodyBlock = createBlock();
    auto &checkBlock = createBlock();
    cf::BranchOp::create(builder, loc, atLeastOnce ? &bodyBlock : &checkBlock);
    if (atLeastOnce)
      bodyBlock.moveBefore(&checkBlock);
 
    // Push the blocks onto the loop stack such that we can continue and break.
    context.loopStack.push_back({&checkBlock, &exitBlock});
    llvm::scope_exit done([&] { context.loopStack.pop_back(); });
 
    // Generate the loop condition check.
    builder.setInsertionPointToEnd(&checkBlock);
    auto cond = context.convertRvalueExpression(condExpr);
    if (!cond)
      return failure();
    cond = builder.createOrFold<moore::BoolCastOp>(loc, cond);
    if (auto ty = dyn_cast<moore::IntType>(cond.getType());
        ty && ty.getDomain() == Domain::FourValued) {
      cond = moore::LogicToIntOp::create(builder, loc, cond);
    }
    cond = moore::ToBuiltinIntOp::create(builder, loc, cond);
    cf::CondBranchOp::create(builder, loc, cond, &bodyBlock, &exitBlock);
 
    // Generate the loop body.
    builder.setInsertionPointToEnd(&bodyBlock);
    if (failed(context.convertStatement(bodyStmt)))
      return failure();
    if (!isTerminated())
      cf::BranchOp::create(builder, loc, &checkBlock);
 
    // If control never reaches the exit block, remove it and mark control flow
    // as terminated. Otherwise we continue inserting ops in the exit block.
    if (exitBlock.hasNoPredecessors()) {
      exitBlock.erase();
      setTerminated();
    } else {
      builder.setInsertionPointToEnd(&exitBlock);
    }
    return success();
  }
 
  LogicalResult visit(const slang::ast::WhileLoopStatement &stmt) {
    return createWhileLoop(stmt.cond, stmt.body, false);
  }
 
  LogicalResult visit(const slang::ast::DoWhileLoopStatement &stmt) {
    return createWhileLoop(stmt.cond, stmt.body, true);
  }
 
  // Handle `forever` loops.
  LogicalResult visit(const slang::ast::ForeverLoopStatement &stmt) {
    // Create the blocks for the loop body and exit.
    auto &exitBlock = createBlock();
    auto &bodyBlock = createBlock();
    cf::BranchOp::create(builder, loc, &bodyBlock);
 
    // Push the blocks onto the loop stack such that we can continue and break.
    context.loopStack.push_back({&bodyBlock, &exitBlock});
    llvm::scope_exit done([&] { context.loopStack.pop_back(); });
 
    // Generate the loop body.
    builder.setInsertionPointToEnd(&bodyBlock);
    if (failed(context.convertStatement(stmt.body)))
      return failure();
    if (!isTerminated())
      cf::BranchOp::create(builder, loc, &bodyBlock);
 
    // If control never reaches the exit block, remove it and mark control flow
    // as terminated. Otherwise we continue inserting ops in the exit block.
    if (exitBlock.hasNoPredecessors()) {
      exitBlock.erase();
      setTerminated();
    } else {
      builder.setInsertionPointToEnd(&exitBlock);
    }
    return success();
  }
 
  // Handle timing control.
  LogicalResult visit(const slang::ast::TimedStatement &stmt) {
    return context.convertTimingControl(stmt.timing, stmt.stmt);
  }
 
  // Handle return statements.
  LogicalResult visit(const slang::ast::ReturnStatement &stmt) {
    Operation *parentOp = builder.getInsertionBlock()
                              ? builder.getInsertionBlock()->getParentOp()
                              : nullptr;
    if (!parentOp)
      return mlir::emitError(loc) << "return statement is not within an op";
 
    if (isa<moore::CoroutineOp, moore::ProcedureOp>(parentOp)) {
      if (stmt.expr)
        return mlir::emitError(loc)
               << "unsupported `return <expr>` in a procedure or task";
      moore::ReturnOp::create(builder, loc);
      setTerminated();
      return success();
    }
 
    auto funcOp = dyn_cast<mlir::func::FuncOp>(parentOp);
    if (!funcOp)
      return mlir::emitError(loc) << "unsupported return statement context";
 
    if (stmt.expr) {
      auto resultTypes = funcOp.getFunctionType().getResults();
      Type resultType = resultTypes.size() == 1 ? resultTypes[0] : Type();
      auto expr = context.convertRvalueExpression(*stmt.expr, resultType);
      if (!expr)
        return failure();
      mlir::func::ReturnOp::create(builder, loc, expr);
    } else {
      mlir::func::ReturnOp::create(builder, loc);
    }
    setTerminated();
    return success();
  }
 
  // Handle continue statements.
  LogicalResult visit(const slang::ast::ContinueStatement &stmt) {
    if (context.loopStack.empty())
      return mlir::emitError(loc,
                             "cannot `continue` without a surrounding loop");
    cf::BranchOp::create(builder, loc, context.loopStack.back().continueBlock);
    setTerminated();
    return success();
  }
 
  // Handle break statements.
  LogicalResult visit(const slang::ast::BreakStatement &stmt) {
    if (context.loopStack.empty())
      return mlir::emitError(loc, "cannot `break` without a surrounding loop");
    cf::BranchOp::create(builder, loc, context.loopStack.back().breakBlock);
    setTerminated();
    return success();
  }
 
  // Handle immediate assertion statements.
  LogicalResult visit(const slang::ast::ImmediateAssertionStatement &stmt) {
    auto cond = context.convertRvalueExpression(stmt.cond);
    cond = context.convertToBool(cond);
    if (!cond)
      return failure();
 
    // Handle assertion statements that don't have an action block.
    if (stmt.ifTrue && stmt.ifTrue->as_if<slang::ast::EmptyStatement>()) {
      auto defer = moore::DeferAssert::Immediate;
      if (stmt.isFinal)
        defer = moore::DeferAssert::Final;
      else if (stmt.isDeferred)
        defer = moore::DeferAssert::Observed;
 
      switch (stmt.assertionKind) {
      case slang::ast::AssertionKind::Assert:
        moore::AssertOp::create(builder, loc, defer, cond, StringAttr{});
        return success();
      case slang::ast::AssertionKind::Assume:
        moore::AssumeOp::create(builder, loc, defer, cond, StringAttr{});
        return success();
      case slang::ast::AssertionKind::CoverProperty:
        moore::CoverOp::create(builder, loc, defer, cond, StringAttr{});
        return success();
      default:
        break;
      }
      mlir::emitError(loc) << "unsupported immediate assertion kind: "
                           << slang::ast::toString(stmt.assertionKind);
      return failure();
    }
 
    // Regard assertion statements with an action block as the "if-else".
    if (auto ty = dyn_cast<moore::IntType>(cond.getType());
        ty && ty.getDomain() == Domain::FourValued) {
      cond = moore::LogicToIntOp::create(builder, loc, cond);
    }
    cond = moore::ToBuiltinIntOp::create(builder, loc, cond);
 
    // Create the blocks for the true and false branches, and the exit block.
    Block &exitBlock = createBlock();
    Block *falseBlock = stmt.ifFalse ? &createBlock() : nullptr;
    Block &trueBlock = createBlock();
    cf::CondBranchOp::create(builder, loc, cond, &trueBlock,
                             falseBlock ? falseBlock : &exitBlock);
 
    // Generate the true branch.
    builder.setInsertionPointToEnd(&trueBlock);
    if (stmt.ifTrue && failed(context.convertStatement(*stmt.ifTrue)))
      return failure();
    if (!isTerminated())
      cf::BranchOp::create(builder, loc, &exitBlock);
 
    if (stmt.ifFalse) {
      // Generate the false branch if present.
      builder.setInsertionPointToEnd(falseBlock);
      if (failed(context.convertStatement(*stmt.ifFalse)))
        return failure();
      if (!isTerminated())
        cf::BranchOp::create(builder, loc, &exitBlock);
    }
 
    // If control never reaches the exit block, remove it and mark control flow
    // as terminated. Otherwise we continue inserting ops in the exit block.
    if (exitBlock.hasNoPredecessors()) {
      exitBlock.erase();
      setTerminated();
    } else {
      builder.setInsertionPointToEnd(&exitBlock);
    }
    return success();
  }
 
  // Handle concurrent assertion statements.
  LogicalResult visit(const slang::ast::ConcurrentAssertionStatement &stmt) {
    auto loc = context.convertLocation(stmt.sourceRange);
 
    // Check for a `disable iff` expression:
    // `disable iff` can only appear at the outermost property that is asserted,
    // and can never be nested.
    // Hence we only need to detect if the top level assertion expression has
    // type DisableIff. (or, if the top level expression is
    // ClockingAssertionExpr, check for DisableIff inside that).
    Value enable;
    Value property;
    // Find the outermost propertySpec that isn't ClockingAssertionExpr
    const slang::ast::AssertionExpr *propertySpec;
    const slang::ast::ClockingAssertionExpr *clocking =
        stmt.propertySpec.as_if<slang::ast::ClockingAssertionExpr>();
    if (clocking)
      propertySpec = &(clocking->expr);
    else
      propertySpec = &(stmt.propertySpec);
 
    if (auto *disableIff =
            propertySpec->as_if<slang::ast::DisableIffAssertionExpr>()) {
      // Lower disableIff by negating it and passing as the "enable" operand
      // to the verif.assert/verif.assume instructions.
      auto disableCond = context.convertRvalueExpression(disableIff->condition);
      auto enableCond = moore::NotOp::create(builder, loc, disableCond);
 
      enable = context.convertToI1(enableCond);
 
      // Add back the outer `ClockingAssertionExpr` if there is one.
      if (clocking) {
        auto clockingExpr = slang::ast::ClockingAssertionExpr(
            clocking->clocking, disableIff->expr);
        property = context.convertAssertionExpression(clockingExpr, loc);
      } else {
        property = context.convertAssertionExpression(disableIff->expr, loc);
      }
    } else {
      property = context.convertAssertionExpression(stmt.propertySpec, loc);
    }
 
    if (!property)
      return failure();
 
    // Handle assertion statements that don't have an action block.
    if (!stmt.ifTrue || stmt.ifTrue->as_if<slang::ast::EmptyStatement>()) {
      switch (stmt.assertionKind) {
      case slang::ast::AssertionKind::Assert:
        verif::AssertOp::create(builder, loc, property, enable, StringAttr{});
        return success();
      case slang::ast::AssertionKind::Assume:
        verif::AssumeOp::create(builder, loc, property, enable, StringAttr{});
        return success();
      default:
        break;
      }
      mlir::emitError(loc) << "unsupported concurrent assertion kind: "
                           << slang::ast::toString(stmt.assertionKind);
      return failure();
    }
 
    mlir::emitError(loc)
        << "concurrent assertion statements with action blocks "
           "are not supported yet";
    return failure();
  }
 
  // According to 1800-2023 Section 21.2.1 "The display and write tasks":
  // >> The $display and $write tasks display their arguments in the same
  // >> order as they appear in the argument list. Each argument can be a
  // >> string literal or an expression that returns a value.
  // According to Section 20.10 "Severity system tasks", the same
  // semantics apply to $fatal, $error, $warning, and $info.
  // This means we must first check whether the first "string-able"
  // argument is a Literal Expression which doesn't represent a fully-formatted
  // string, otherwise we convert it to a FormatStringType.
  FailureOr<Value>
  getDisplayMessage(std::span<const slang::ast::Expression *const> args) {
    if (args.size() == 0)
      return Value{};
 
    // Handle the string formatting.
    // If the second argument is a Literal of some type, we should either
    // treat it as a literal-to-be-formatted or a FormatStringType.
    // In this check we use a StringLiteral, but slang allows casting between
    // any literal expressions (strings, integers, reals, and time at least) so
    // this is short-hand for "any value literal"
    if (args[0]->as_if<slang::ast::StringLiteral>()) {
      return context.convertFormatString(args, loc);
    }
    // Check if there's only one argument and it's a FormatStringType
    if (args.size() == 1) {
      return context.convertRvalueExpression(
          *args[0], builder.getType<moore::FormatStringType>());
    }
    // Otherwise this looks invalid. Raise an error.
    return emitError(loc) << "Failed to convert Display Message!";
  }
 
  /// Convert a `$readmemb`/`$readmemh` system task call into a
  /// `moore.builtin.readmem` op. See IEEE 1800-2017 § 21.4.
  LogicalResult
  convertReadMemTask(std::span<const slang::ast::Expression *const> args,
                     bool isBinary) {
    assert(args.size() >= 2 && args.size() <= 4 &&
           "$readmemh/$readmemb takes 2 to 4 arguments");
 
    auto i32Ty = moore::IntType::getInt(builder.getContext(), 32);
    auto filename = context.convertRvalueExpression(
        *args[0], moore::StringType::get(builder.getContext()));
    if (!filename)
      return failure();
 
    const auto *destExpr = args[1];
 
    // Slang wraps the memory argument in an assignment to the lvalue;
    // unwrap it to get at the memory itslef.
    if (const auto *assign =
            destExpr->as_if<slang::ast::AssignmentExpression>())
      destExpr = &assign->left();
 
    // The memory may use slice syntax on its rightmost specified dimension.
    // The slice only narrows the address window of the selected array's highest
    // dimension; the destination stays the full array.
    Value sliceLeft, sliceRight;
    if (const auto *rangeExpr =
            destExpr->as_if<slang::ast::RangeSelectExpression>()) {
      if (rangeExpr->getSelectionKind() !=
          slang::ast::RangeSelectionKind::Simple) {
        mlir::emitError(loc)
            << "unsupported: indexed part-select on $readmem memory";
        return failure();
      }
 
      sliceLeft = context.convertRvalueExpression(rangeExpr->left(), i32Ty);
      sliceRight = context.convertRvalueExpression(rangeExpr->right(), i32Ty);
 
      if (!sliceLeft || !sliceRight)
        return failure();
 
      destExpr = &rangeExpr->value();
    }
 
    auto dest = context.convertLvalueExpression(*destExpr);
    if (!dest)
      return failure();
 
    // Collect the declared low bound and direction of every unpacked dimension
    // (outermost first): the Moore array types do not carry them, but the
    // row-major file layout (§21.4.3) and the address mapping of the lowering
    // depend on them. Queues load with their current size fixed (§21.4.1).
    const auto *curTy = &destExpr->type->getCanonicalType();
    SmallVector<int64_t> dimLows;
    SmallVector<bool> dimDescs;
    const slang::ast::Type *elemSvTy = curTy;
 
    if (curTy->isAssociativeArray()) {
      mlir::emitError(loc) << "unsupported: $readmem into associative array";
      return failure();
    }
 
    if (const auto *queueTy = curTy->as_if<slang::ast::QueueType>()) {
      dimLows.push_back(0);
      dimDescs.push_back(false);
      elemSvTy = &queueTy->elementType.getCanonicalType();
    } else if (curTy->as_if<slang::ast::DynamicArrayType>()) {
      mlir::emitError(loc) << "unsupported: $readmem into dynamic array";
      return failure();
    } else {
      while (const auto *fixedArr =
                 curTy->as_if<slang::ast::FixedSizeUnpackedArrayType>()) {
        dimLows.push_back(fixedArr->range.lower());
        dimDescs.push_back(fixedArr->range.isDescending());
        curTy = &fixedArr->elementType.getCanonicalType();
      }
      elemSvTy = curTy;
    }
 
    if (dimLows.empty()) {
      mlir::emitError(loc) << "$readmem memory must be an unpacked array";
      return failure();
    }
 
    // The file contains binary or hexadecimal numbers, so elements must be
    // packed data.
    if (!elemSvTy->isIntegral()) {
      mlir::emitError(loc) << "unsupported: $readmem element type "
                           << elemSvTy->toString();
      return failure();
    }
 
    // Values outside the enumeration must be rejected during the load. Collect
    // the legal values so the lowering can check membership; wider enumerations
    // cannot be represented in the attribute.
    DenseI64ArrayAttr enumValuesAttr;
    if (const auto *enumTy = elemSvTy->as_if<slang::ast::EnumType>()) {
      if (enumTy->getBitWidth() > 64) {
        mlir::emitError(loc)
            << "unsupported: $readmem into enumeration wider than 64 bits";
        return failure();
      }
      SmallVector<int64_t> vals;
      for (const auto &ev : enumTy->values()) {
        auto v = ev.getValue().integer().as<int64_t>();
        if (!v) {
          mlir::emitError(loc)
              << "unsupported: $readmem enumeration value with unknown bits";
          return failure();
        }
        vals.push_back(*v);
      }
      enumValuesAttr = builder.getDenseI64ArrayAttr(vals);
    }
 
    Value startAddr;
    if (args.size() >= 3 &&
        args[2]->kind != slang::ast::ExpressionKind::EmptyArgument) {
      startAddr = context.convertRvalueExpression(*args[2], i32Ty);
      if (!startAddr)
        return failure();
    }
 
    Value finishAddr;
    if (args.size() >= 4 &&
        args[3]->kind != slang::ast::ExpressionKind::EmptyArgument) {
      finishAddr = context.convertRvalueExpression(*args[3], i32Ty);
      if (!finishAddr)
        return failure();
    }
 
    auto base = isBinary ? moore::MemBase::Binary : moore::MemBase::Hex;
    moore::ReadMemBIOp::create(
        builder, loc, filename, dest,
        moore::MemBaseAttr::get(builder.getContext(), base), startAddr,
        finishAddr, sliceLeft, sliceRight,
        builder.getDenseI64ArrayAttr(dimLows),
        builder.getDenseBoolArrayAttr(dimDescs), enumValuesAttr);
    return success();
  }
 
  /// Handle the subset of system calls that return no result value. Return
  /// true if the called system task could be handled, false otherwise. Return
  /// failure if an error occurred.
  FailureOr<bool>
  visitSystemCall(const slang::ast::ExpressionStatement &stmt,
                  const slang::ast::CallExpression &expr,
                  const slang::ast::CallExpression::SystemCallInfo &info) {
    using ksn = slang::parsing::KnownSystemName;
    const auto &subroutine = *info.subroutine;
    auto nameId = subroutine.knownNameId;
    auto args = expr.arguments();
 
    // The `$cast` system call is handled by `Context::convertSystemCall` in the
    // `Expressions.cpp` file. Skip it is order to avoid visiting the
    // `EmptyArgument` node.
    if (nameId == ksn::Cast) {
      return false;
    }
 
    // Simulation Control Tasks
 
    if (nameId == ksn::Stop) {
      createFinishMessage(args.size() >= 1 ? args[0] : nullptr);
      moore::StopBIOp::create(builder, loc);
      return true;
    }
 
    if (nameId == ksn::Finish) {
      createFinishMessage(args.size() >= 1 ? args[0] : nullptr);
      moore::FinishBIOp::create(builder, loc, 0);
      moore::UnreachableOp::create(builder, loc);
      setTerminated();
      return true;
    }
 
    if (nameId == ksn::Exit) {
      // Calls to `$exit` from outside a `program` are ignored. Since we don't
      // yet support programs, there is nothing to do here.
      // TODO: Fix this once we support programs.
      return true;
    }
 
    // Timescale tasks (`$printtimescale`)
 
    if (nameId == ksn::PrintTimeScale) {
      auto message = moore::FormatLiteralOp::create(
          builder, loc, buildPrintTimeScaleMessage(context, args));
      moore::DisplayBIOp::create(builder, loc, message);
      return true;
    }
 
    // Display and Write Tasks (`$display[boh]?` or `$write[boh]?` or
    // `$fdisplay[boh]?` or `$fwrite[boh]?` or `$swrite[boh]` or `$sformat`)
 
    using moore::IntFormat;
    bool isDisplay = false;
    bool isFDisplay = false;
    bool isSWrite = false;
    bool isSFormat = false;
    bool appendNewline = false;
    IntFormat defaultFormat = IntFormat::Decimal;
    switch (nameId) {
    case ksn::Display:
      isDisplay = true;
      appendNewline = true;
      break;
    case ksn::DisplayB:
      isDisplay = true;
      appendNewline = true;
      defaultFormat = IntFormat::Binary;
      break;
    case ksn::DisplayO:
      isDisplay = true;
      appendNewline = true;
      defaultFormat = IntFormat::Octal;
      break;
    case ksn::DisplayH:
      isDisplay = true;
      appendNewline = true;
      defaultFormat = IntFormat::HexLower;
      break;
    case ksn::Write:
      isDisplay = true;
      break;
    case ksn::WriteB:
      isDisplay = true;
      defaultFormat = IntFormat::Binary;
      break;
    case ksn::WriteO:
      isDisplay = true;
      defaultFormat = IntFormat::Octal;
      break;
    case ksn::WriteH:
      isDisplay = true;
      defaultFormat = IntFormat::HexLower;
      break;
    case ksn::FDisplay:
      isFDisplay = true;
      appendNewline = true;
      break;
    case ksn::FDisplayB:
      isFDisplay = true;
      appendNewline = true;
      defaultFormat = IntFormat::Binary;
      break;
    case ksn::FDisplayO:
      isFDisplay = true;
      appendNewline = true;
      defaultFormat = IntFormat::Octal;
      break;
    case ksn::FDisplayH:
      isFDisplay = true;
      appendNewline = true;
      defaultFormat = IntFormat::HexLower;
      break;
    case ksn::FWrite:
      isFDisplay = true;
      break;
    case ksn::FWriteB:
      isFDisplay = true;
      defaultFormat = IntFormat::Binary;
      break;
    case ksn::FWriteO:
      isFDisplay = true;
      defaultFormat = IntFormat::Octal;
      break;
    case ksn::FWriteH:
      isFDisplay = true;
      defaultFormat = IntFormat::HexLower;
      break;
    case ksn::SFormat:
      isSFormat = true;
      break;
    case ksn::SWrite:
      isSWrite = true;
      break;
    case ksn::SWriteB:
      isSWrite = true;
      defaultFormat = IntFormat::Binary;
      break;
    case ksn::SWriteO:
      isSWrite = true;
      defaultFormat = IntFormat::Octal;
      break;
    case ksn::SWriteH:
      isSWrite = true;
      defaultFormat = IntFormat::HexLower;
      break;
    default:
      break;
    }
 
    if (isDisplay) {
      auto message =
          context.convertFormatString(args, loc, defaultFormat, appendNewline);
      if (failed(message))
        return failure();
      if (*message == Value{})
        return true;
      moore::DisplayBIOp::create(builder, loc, *message);
      return true;
    }
 
    if (isFDisplay) {
      assert(!args.empty() && "$fdisplay/$fwrite takes at least 1 argument");
 
      auto fd = context.convertRvalueExpression(
          *args[0], moore::IntType::getInt(builder.getContext(), 32));
      if (!fd)
        return failure();
      args = args.subspan(1);
 
      auto message =
          context.convertFormatString(args, loc, defaultFormat, appendNewline);
      if (failed(message))
        return failure();
      if (*message == Value{})
        return true;
      moore::FDisplayBIOp::create(builder, loc, fd, *message);
      return true;
    }
 
    // According to IEEE 1800-2023 Section 21.3.3 "Formatting data to a
    // string" the first argument of $sformat/$swrite is its output; the
    // other arguments work like a FormatString.
    // In Moore we only support writing to a location if it is a reference;
    // However, Section 21.3.3 explains that the output of $sformat/$swrite
    // is assigned as if it were cast from a string literal (Section 5.9),
    // so this implementation casts the string to the target value.
    if (isSWrite || isSFormat) {
      if (isSFormat && args.size() < 2)
        return emitError(loc) << "$sformat requires at least 2 arguments";
      if (isSWrite && args.size() < 1)
        return emitError(loc) << "$swrite requires at least 1 argument";
 
      auto fmtValue =
          context.convertFormatString(args.subspan(1), loc, defaultFormat,
                                      /*appendNewline=*/false);
      if (failed(fmtValue))
        return failure();
      if (*fmtValue == Value{})
        return true;
      auto strValue =
          moore::FormatStringToStringOp::create(builder, loc, *fmtValue);
      auto *lhsExpr = args[0];
      if (auto *assignExpr =
              lhsExpr->as_if<slang::ast::AssignmentExpression>()) {
        auto lhs = context.convertLvalueExpression(assignExpr->left());
        if (!lhs)
          return failure();
        auto convertedValue = context.materializeConversion(
            cast<moore::RefType>(lhs.getType()).getNestedType(), strValue,
            false, loc);
        if (!convertedValue)
          return failure();
        moore::BlockingAssignOp::create(builder, loc, lhs, convertedValue);
        return true;
      }
      return failure();
    }
 
    // Severity Tasks
    using moore::Severity;
    std::optional<Severity> severity;
    if (nameId == ksn::Info)
      severity = Severity::Info;
    else if (nameId == ksn::Warning)
      severity = Severity::Warning;
    else if (nameId == ksn::Error)
      severity = Severity::Error;
    else if (nameId == ksn::Fatal)
      severity = Severity::Fatal;
 
    if (severity) {
      // The `$fatal` task has an optional leading verbosity argument.
      const slang::ast::Expression *verbosityExpr = nullptr;
      if (severity == Severity::Fatal && args.size() >= 1) {
        verbosityExpr = args[0];
        args = args.subspan(1);
      }
 
      FailureOr<Value> maybeMessage = getDisplayMessage(args);
      if (failed(maybeMessage))
        return failure();
      auto message = maybeMessage.value();
 
      if (message == Value{})
        message = moore::FormatLiteralOp::create(builder, loc, "");
      moore::SeverityBIOp::create(builder, loc, *severity, message);
 
      // Handle the `$fatal` case which behaves like a `$finish`.
      if (severity == Severity::Fatal) {
        createFinishMessage(verbosityExpr);
        moore::FinishBIOp::create(builder, loc, 1);
        moore::UnreachableOp::create(builder, loc);
        setTerminated();
      }
      return true;
    }
 
    // File I/O Tasks
 
    if (nameId == ksn::FClose) {
      assert(args.size() == 1 && "$fclose takes 1 argument");
      auto fd = context.convertRvalueExpression(
          *args[0], moore::IntType::getInt(builder.getContext(), 32));
      if (!fd)
        return failure();
      moore::FCloseBIOp::create(builder, loc, fd);
      return true;
    }
 
    if (nameId == ksn::FFlush) {
      assert(args.size() <= 1 && "$fflush takes at most 1 argument");
      Value fd;
      if (args.size() == 1) {
        fd = context.convertRvalueExpression(
            *args[0], moore::IntType::getInt(builder.getContext(), 32));
        if (!fd)
          return failure();
      }
      moore::FFlushBIOp::create(builder, loc, fd);
      return true;
    }
 
    if (nameId == ksn::ReadMemH || nameId == ksn::ReadMemB) {
      if (failed(convertReadMemTask(args, nameId == ksn::ReadMemB)))
        return failure();
      return true;
    }
 
    // String Tasks
    if (args.size() >= 1 && args[0]->type->isString()) {
      auto str = context.convertLvalueExpression(*args[0]);
 
      if (nameId == ksn::Putc) {
        // Slang already checks the arity of string tasks.
        assert(args.size() == 3 && "`putc` takes 3 arguments");
        auto index = context.convertRvalueExpression(*args[1]);
        auto character = context.convertRvalueExpression(*args[2]);
        moore::StringPutOp::create(builder, loc, str, index, character);
        return true;
      }
 
      if (nameId == ksn::IToA || nameId == ksn::HexToA ||
          nameId == ksn::OctToA || nameId == ksn::BinToA) {
        // Slang already checks the arity of string tasks.
        assert(args.size() == 2 && "`itoa/hex/oct/bin` takes 2 arguments");
        auto integerType = moore::IntType::getLogic(builder.getContext(), 32);
        auto input = context.convertRvalueExpression(*args[1], integerType);
 
        switch (nameId) {
        case ksn::IToA:
          moore::StringItoaOp::create(builder, loc, str, input);
          break;
        case ksn::HexToA:
          moore::StringHextoaOp::create(builder, loc, str, input);
          break;
        case ksn::OctToA:
          moore::StringOcttoaOp::create(builder, loc, str, input);
          break;
        case ksn::BinToA:
          moore::StringBintoaOp::create(builder, loc, str, input);
          break;
        default:
          llvm_unreachable("unexpected ASCII integer to string conversion");
          return false;
        }
        return true;
      }
 
      if (nameId == ksn::RealToA) {
        // Slang already checks the arity of string tasks.
        assert(args.size() == 2 && "`realtoa` takes 2 arguments");
        auto realType =
            moore::RealType::get(context.getContext(), moore::RealWidth::f64);
        auto input = context.convertRvalueExpression(*args[1], realType);
        moore::StringRealtoaOp::create(builder, loc, str, input);
        return true;
      }
      return false;
    }
 
    // Queue Tasks
    if (args.size() >= 1 && args[0]->type->isQueue()) {
      auto queue = context.convertLvalueExpression(*args[0]);
 
      // `delete` has two functions: If there is an index passed, then it
      // deletes that specific element, otherwise, it clears the entire queue.
      if (nameId == ksn::Delete) {
        if (args.size() == 1) {
          moore::QueueClearOp::create(builder, loc, queue);
          return true;
        }
        if (args.size() == 2) {
          auto index = context.convertRvalueExpression(*args[1]);
          moore::QueueDeleteOp::create(builder, loc, queue, index);
          return true;
        }
      } else if (nameId == ksn::Insert && args.size() == 3) {
        auto index = context.convertRvalueExpression(*args[1]);
        auto item = context.convertRvalueExpression(*args[2]);
 
        moore::QueueInsertOp::create(builder, loc, queue, index, item);
        return true;
      } else if (nameId == ksn::PushBack && args.size() == 2) {
        auto item = context.convertRvalueExpression(*args[1]);
        moore::QueuePushBackOp::create(builder, loc, queue, item);
        return true;
      } else if (nameId == ksn::PushFront && args.size() == 2) {
        auto item = context.convertRvalueExpression(*args[1]);
        moore::QueuePushFrontOp::create(builder, loc, queue, item);
        return true;
      }
 
      return false;
    }
 
    // Associative array tasks
    if (args.size() >= 1 && args[0]->type->isAssociativeArray()) {
      auto assocArray = context.convertLvalueExpression(*args[0]);
 
      // `delete` has two functions: If there is an index passed, then it
      // deletes that specific element, otherwise, it clears the entire
      // associative array.
      if (nameId == ksn::Delete) {
        if (args.size() == 1) {
          moore::AssocArrayClearOp::create(builder, loc, assocArray);
          return true;
        }
        if (args.size() == 2) {
          auto index = context.convertRvalueExpression(*args[1]);
          moore::AssocArrayDeleteOp::create(builder, loc, assocArray, index);
          return true;
        }
      }
    }
 
    // Monitor enable/disable tasks (`$monitoron`, `$monitoroff`)
    if (nameId == ksn::MonitorOn || nameId == ksn::MonitorOff) {
      context.ensureMonitorGlobals();
      bool enable = (nameId == ksn::MonitorOn);
      auto enabledRef = moore::GetGlobalVariableOp::create(
          context.builder, loc, context.monitorEnabledGlobal);
      auto value = moore::ConstantOp::create(context.builder, loc,
                                             moore::Domain::TwoValued, enable);
      moore::BlockingAssignOp::create(context.builder, loc, enabledRef, value);
      return true;
    }
 
    // Monitor tasks (`$monitor[boh]?`)
    if (nameId == ksn::Monitor || nameId == ksn::MonitorB ||
        nameId == ksn::MonitorO || nameId == ksn::MonitorH) {
      context.ensureMonitorGlobals();
 
      // Allocate a unique ID for this monitor.
      unsigned myId = context.nextMonitorId++;
 
      // Emit code to activate this monitor by setting the active_id global.
      auto i32Type = moore::IntType::getInt(context.getContext(), 32);
      auto idConst =
          moore::ConstantOp::create(context.builder, loc, i32Type, myId);
      auto activeRef = moore::GetGlobalVariableOp::create(
          context.builder, loc, context.monitorActiveIdGlobal);
      moore::BlockingAssignOp::create(context.builder, loc, activeRef, idConst);
 
      // Queue this monitor for processing at module level.
      context.pendingMonitors.push_back({myId, loc, &expr});
 
      return true;
    }
 
    if (nameId == ksn::TimeFormat) {
      context.ensureTimeFormatGlobal();
      auto i32Ty = moore::IntType::getInt(context.getContext(), 32);
      auto strTy = moore::StringType::get(context.getContext());
 
      if (args.empty()) {
        auto defaults = getDefaultTimeFormatValues(context.builder, loc,
                                                   context.getContext());
        std::array<StringRef, 4> argNames = {"unit", "precision", "suffix",
                                             "min_width"};
        for (auto [name, value] : llvm::zip(argNames, defaults)) {
          auto base = moore::GetGlobalVariableOp::create(
              context.builder, loc, context.timeFormatGlobal);
          auto fieldRef = moore::StructExtractRefOp::create(
              context.builder, loc,
              moore::RefType::get(cast<moore::UnpackedType>(value.getType())),
              StringAttr::get(context.getContext(), name), base);
          moore::BlockingAssignOp::create(context.builder, loc, fieldRef,
                                          value);
        }
        return true;
      }
 
      std::array<std::pair<StringRef, Type>, 4> argsTypes = {{
          {"unit", i32Ty},
          {"precision", i32Ty},
          {"suffix", strTy},
          {"min_width", i32Ty},
      }};
 
      for (auto [i, arg] : llvm::enumerate(argsTypes)) {
        if (args.size() <= i)
          break;
        auto value = context.convertRvalueExpression(*args[i], arg.second);
        if (!value)
          return failure();
 
        auto base = moore::GetGlobalVariableOp::create(
            context.builder, loc, context.timeFormatGlobal);
        auto fieldRef = moore::StructExtractRefOp::create(
            context.builder, loc,
            moore::RefType::get(cast<moore::UnpackedType>(arg.second)),
            StringAttr::get(context.getContext(), arg.first), base);
        moore::BlockingAssignOp::create(context.builder, loc, fieldRef, value);
      }
      return true;
    }
 
    // Give up on any other system tasks. These will be tried again as an
    // expression later.
    return false;
  }
 
  /// Create the optional diagnostic message print for finish-like ops.
  void createFinishMessage(const slang::ast::Expression *verbosityExpr) {
    unsigned verbosity = 1;
    if (verbosityExpr) {
      auto value =
          context.evaluateConstant(*verbosityExpr).integer().as<unsigned>();
      assert(value && "Slang guarantees constant verbosity parameter");
      verbosity = *value;
    }
    if (verbosity == 0)
      return;
    moore::FinishMessageBIOp::create(builder, loc, verbosity > 1);
  }
 
  // Handle event trigger statements.
  LogicalResult visit(const slang::ast::EventTriggerStatement &stmt) {
    if (stmt.timing) {
      mlir::emitError(loc) << "unsupported delayed event trigger";
      return failure();
    }
 
    // Events are lowered to `i1` signals. Get an lvalue ref to the signal such
    // that we can assign to it.
    auto target = context.convertLvalueExpression(stmt.target);
    if (!target)
      return failure();
 
    // Read and invert the current value of the signal. Writing this inverted
    // value to the signal is our event signaling mechanism.
    Value inverted = moore::ReadOp::create(builder, loc, target);
    inverted = moore::NotOp::create(builder, loc, inverted);
 
    if (stmt.isNonBlocking)
      moore::NonBlockingAssignOp::create(builder, loc, target, inverted);
    else
      moore::BlockingAssignOp::create(builder, loc, target, inverted);
    return success();
  }
 
  // Handle `wait` statements
  LogicalResult visit(const slang::ast::WaitStatement &stmt) {
    auto waitOp = moore::WaitLevelOp::create(builder, loc);
    {
      OpBuilder::InsertionGuard guard(builder);
      builder.setInsertionPointToStart(&waitOp.getBody().emplaceBlock());
      auto cond = context.convertRvalueExpression(stmt.cond);
      if (!cond)
        return failure();
      cond = builder.createOrFold<moore::BoolCastOp>(loc, cond);
      moore::DetectLevelOp::create(builder, loc, cond);
    }
    // Handle optional post-wait operation as if it were a separate statement
    if (failed(context.convertStatement(stmt.stmt)))
      return failure();
 
    return success();
  }
 
  LogicalResult visit(const slang::ast::WaitForkStatement &stmt) {
    moore::WaitForkOp::create(builder, loc);
    return success();
  }
 
  /// Emit an error for all other statements.
  template <typename T>
  LogicalResult visit(T &&stmt) {
    mlir::emitError(loc, "unsupported statement: ")
        << slang::ast::toString(stmt.kind);
    return mlir::failure();
  }
 
  LogicalResult visitInvalid(const slang::ast::Statement &stmt) {
    mlir::emitError(loc, "invalid statement: ")
        << slang::ast::toString(stmt.kind);
    return mlir::failure();
  }
};
} // namespace
 
LogicalResult Context::convertStatement(const slang::ast::Statement &stmt) {
  assert(builder.getInsertionBlock());
  auto loc = convertLocation(stmt.sourceRange);
  return stmt.visit(StmtVisitor(*this, loc));
}
// NOLINTEND(misc-no-recursion)
 
//===----------------------------------------------------------------------===//
// Monitor support
//===----------------------------------------------------------------------===//
 
void Context::ensureMonitorGlobals() {
  // If globals already exist, nothing to do.
  if (monitorActiveIdGlobal && monitorEnabledGlobal)
    return;
 
  // Save current builder position and insert at the start of the module.
  OpBuilder::InsertionGuard guard(builder);
  builder.setInsertionPointToStart(intoModuleOp.getBody());
 
  auto loc = intoModuleOp.getLoc();
  auto i32Type = moore::IntType::getInt(getContext(), 32);
  auto i1Type = moore::IntType::getInt(getContext(), 1);
 
  // Create "active_id" global variable. Index 0 indicates no monitor
  // is active.
  monitorActiveIdGlobal = moore::GlobalVariableOp::create(
      builder, loc, "__monitor_active_id", /*sym_visibility=*/{}, i32Type);
  {
    OpBuilder::InsertionGuard initGuard(builder);
    builder.setInsertionPointToStart(
        &monitorActiveIdGlobal.getInitRegion().emplaceBlock());
    auto zero = moore::ConstantOp::create(builder, loc, i32Type, 0);
    moore::YieldOp::create(builder, loc, zero);
  }
  symbolTable.insert(monitorActiveIdGlobal);
 
  // Create "enabled" global variable.
  monitorEnabledGlobal = moore::GlobalVariableOp::create(
      builder, loc, "__monitor_enabled", /*sym_visibility=*/{}, i1Type);
  {
    OpBuilder::InsertionGuard initGuard(builder);
    builder.setInsertionPointToStart(
        &monitorEnabledGlobal.getInitRegion().emplaceBlock());
    auto trueVal =
        moore::ConstantOp::create(builder, loc, moore::Domain::TwoValued, true);
    moore::YieldOp::create(builder, loc, trueVal);
  }
  symbolTable.insert(monitorEnabledGlobal);
}
 
LogicalResult Context::flushPendingMonitors() {
  using ksn = slang::parsing::KnownSystemName;
  for (auto &pending : pendingMonitors) {
    auto &call = *pending.call;
    auto loc = pending.loc;
 
    // Extract the SystemCallInfo from the call's subroutine variant.
    auto &info =
        std::get<slang::ast::CallExpression::SystemCallInfo>(call.subroutine);
    auto nameId = info.subroutine->knownNameId;
 
    // Determine the default format based on the system call name.
    auto defaultFormat = moore::IntFormat::Decimal;
    switch (nameId) {
    case ksn::MonitorB:
      defaultFormat = moore::IntFormat::Binary;
      break;
    case ksn::MonitorO:
      defaultFormat = moore::IntFormat::Octal;
      break;
    case ksn::MonitorH:
      defaultFormat = moore::IntFormat::HexLower;
      break;
    default:
      break;
    }
 
    // Create an always_comb procedure for this monitor. This will implement the
    // semantics of printing an updated message whenever one of the input
    // signals changes.
    auto alwaysProc = moore::ProcedureOp::create(
        builder, loc, moore::ProcedureKind::AlwaysComb);
    OpBuilder::InsertionGuard guard(builder);
    builder.setInsertionPointToStart(&alwaysProc.getBody().emplaceBlock());
 
    // Convert the format string and arguments.
    auto message = convertFormatString(call.arguments(), loc, defaultFormat,
                                       /*appendNewline=*/true);
    if (failed(message))
      return failure();
 
    // Check if this monitor is active and enabled.
    auto i32Type = moore::IntType::getInt(getContext(), 32);
    auto myId = moore::ConstantOp::create(builder, loc, i32Type, pending.id);
    Value isActive =
        moore::GetGlobalVariableOp::create(builder, loc, monitorActiveIdGlobal);
    isActive = moore::ReadOp::create(builder, loc, isActive);
    isActive = moore::EqOp::create(builder, loc, isActive, myId);
 
    Value enabled =
        moore::GetGlobalVariableOp::create(builder, loc, monitorEnabledGlobal);
    enabled = moore::ReadOp::create(builder, loc, enabled);
    enabled = moore::AndOp::create(builder, loc, isActive, enabled);
    enabled = moore::ToBuiltinIntOp::create(builder, loc, enabled);
 
    // Branch to a print or skip block based on whether the monitor is enabled
    // or not.
    auto &printBlock = alwaysProc.getBody().emplaceBlock();
    auto &skipBlock = alwaysProc.getBody().emplaceBlock();
    cf::CondBranchOp::create(builder, loc, enabled, &printBlock, &skipBlock);
 
    // Display the formatted message if one was created, and the monitor is
    // enabled.
    builder.setInsertionPointToStart(&printBlock);
    if (*message)
      moore::DisplayBIOp::create(builder, loc, *message);
    moore::ReturnOp::create(builder, loc);
 
    // Otherwise just return.
    builder.setInsertionPointToStart(&skipBlock);
    moore::ReturnOp::create(builder, loc);
  }
 
  pendingMonitors.clear();
  return success();
}
 
//===----------------------------------------------------------------------===//
// Time format support
//===----------------------------------------------------------------------===//
 
void Context::ensureTimeFormatGlobal() {
  if (timeFormatGlobal)
    return;
  OpBuilder::InsertionGuard guard(builder);
  builder.setInsertionPointToStart(intoModuleOp.getBody());
 
  auto loc = intoModuleOp.getLoc();
  auto i32Ty = moore::IntType::getInt(getContext(), 32);
  auto strTy = moore::StringType::get(getContext());
 
  SmallVector<moore::StructLikeMember> members{
      {StringAttr::get(getContext(), "unit"), i32Ty},
      {StringAttr::get(getContext(), "precision"), i32Ty},
      {StringAttr::get(getContext(), "suffix"), strTy},
      {StringAttr::get(getContext(), "min_width"), i32Ty},
  };
  auto structTy = moore::UnpackedStructType::get(getContext(), members);
 
  timeFormatGlobal = moore::GlobalVariableOp::create(
      builder, loc, "__timeformat_state", /*sym_visibility=*/{}, structTy);
  {
    OpBuilder::InsertionGuard initGuard(builder);
    builder.setInsertionPointToStart(
        &timeFormatGlobal.getInitRegion().emplaceBlock());
    auto defaults = getDefaultTimeFormatValues(builder, loc, getContext());
    auto init = moore::StructCreateOp::create(builder, loc, structTy,
                                              ValueRange(defaults));
    moore::YieldOp::create(builder, loc, init);
  }
  symbolTable.insert(timeFormatGlobal);
}