LinkModules.cpp

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//===- OMLinkModules.cpp - OM Linker pass -----------------------*- C++ -*-===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
// Contains the definitions of the OM Linker pass.
//
//===----------------------------------------------------------------------===//
 
#include "circt/Dialect/OM/OMOps.h"
#include "circt/Dialect/OM/OMPasses.h"
#include "circt/Support/Namespace.h"
#include "mlir/IR/Block.h"
#include "mlir/IR/Builders.h"
#include "mlir/IR/BuiltinOps.h"
#include "mlir/IR/SymbolTable.h"
#include "mlir/IR/Threading.h"
#include "mlir/Pass/Pass.h"
 
#include <memory>
 
namespace circt {
namespace om {
#define GEN_PASS_DEF_LINKMODULES
#include "circt/Dialect/OM/OMPasses.h.inc"
} // namespace om
} // namespace circt
 
using namespace circt;
using namespace om;
using namespace mlir;
using namespace llvm;
 
namespace {
// A map from a pair of enclosing module op and old symbol to a new symbol.
using SymMappingTy =
    llvm::DenseMap<std::pair<ModuleOp, StringAttr>, StringAttr>;
 
struct ModuleInfo {
  ModuleInfo(mlir::ModuleOp module) : module(module) {
    block = std::make_unique<Block>();
  }
 
  // Populate `symbolToClasses`.
  LogicalResult initialize();
 
  // Update symbols based on the mapping and erase external classes.
  void postProcess(const SymMappingTy &symMapping);
 
  // A map from symbols to classes.
  llvm::DenseMap<StringAttr, ClassLike> symbolToClasses;
 
  // A target module.
  ModuleOp module;
 
  // A block to store original operations.
  std::unique_ptr<Block> block;
};
 
struct LinkModulesPass
    : public circt::om::impl::LinkModulesBase<LinkModulesPass> {
  using Base::Base;
  void runOnOperation() override;
};
 
} // namespace
 
LogicalResult ModuleInfo::initialize() {
  for (auto &op : llvm::make_early_inc_range(module.getOps())) {
    if (auto classLike = dyn_cast<ClassLike>(op))
      symbolToClasses.insert({classLike.getSymNameAttr(), classLike});
    else {
      // Keep the op.
      op.moveBefore(block.get(), block->end());
    }
  }
  return success();
}
 
void ModuleInfo::postProcess(const SymMappingTy &symMapping) {
  AttrTypeReplacer replacer;
  replacer.addReplacement(
      // Update class types when their symbols were renamed.
      [&](om::ClassType classType) -> std::pair<mlir::Type, WalkResult> {
        auto it = symMapping.find({module, classType.getClassName().getAttr()});
        // No change.
        if (it == symMapping.end())
          return {classType, WalkResult::skip()};
        return {om::ClassType::get(classType.getContext(),
                                   FlatSymbolRefAttr::get(it->second)),
                WalkResult::skip()};
      });
 
  module.walk<WalkOrder::PreOrder>([&](Operation *op) {
    // External modules must be erased.
    if (isa<ClassExternOp>(op)) {
      op->erase();
      // ClassExternFieldOp will be deleted as well.
      return WalkResult::skip();
    }
 
    if (auto classOp = dyn_cast<ClassOp>(op)) {
      // Update its class name if changed.
      auto it = symMapping.find({module, classOp.getNameAttr()});
      if (it != symMapping.end())
        classOp.setSymNameAttr(it->second);
      classOp.replaceFieldTypes(replacer);
    } else if (auto objectOp = dyn_cast<ObjectOp>(op)) {
      // Update its class name if changed..
      auto it = symMapping.find({module, objectOp.getClassNameAttr()});
      if (it != symMapping.end())
        objectOp.setClassNameAttr(it->second);
    }
 
    // Otherwise update om.class types.
    replacer.replaceElementsIn(op,
                               /*replaceAttrs=*/false,
                               /*replaceLocs=*/false,
                               /*replaceTypes=*/true);
    return WalkResult::advance();
  });
}
 
// Return a failure if classes cannot be resolved. Return true if
// it's necessary to rename symbols.
static FailureOr<bool> resolveClasses(StringAttr name,
                                      ArrayRef<ClassLike> classes) {
  bool existExternalClass = false;
  size_t countDefinition = 0;
  ClassOp classOp;
 
  for (auto op : classes) {
    if (isa<ClassExternOp>(op))
      existExternalClass = true;
    else {
      classOp = cast<ClassOp>(op);
      ++countDefinition;
    }
  }
 
  // There must be exactly one definition if the symbol was referred by an
  // external class.
  if (existExternalClass && countDefinition != 1) {
    SmallVector<Location> classExternLocs;
    SmallVector<Location> classLocs;
    for (auto op : classes)
      (isa<ClassExternOp>(op) ? classExternLocs : classLocs)
          .push_back(op.getLoc());
 
    auto diag = emitError(classExternLocs.front())
                << "class " << name << " is declared as an external class but "
                << (countDefinition == 0 ? "there is no definition"
                                         : "there are multiple definitions");
    for (auto loc : ArrayRef(classExternLocs).drop_front())
      diag.attachNote(loc) << "class " << name << " is declared here as well";
 
    if (countDefinition != 0) {
      // There are multiple definitions.
      for (auto loc : classLocs)
        diag.attachNote(loc) << "class " << name << " is defined here";
    }
    return failure();
  }
 
  if (!existExternalClass)
    return countDefinition != 1;
 
  assert(classOp && countDefinition == 1);
 
  // Raise errors if linked external modules are not compatible with the
  // definition.
  auto emitError = [&](Operation *op) {
    auto diag = op->emitError()
                << "failed to link class " << name
                << " since declaration doesn't match the definition: ";
    diag.attachNote(classOp.getLoc()) << "definition is here";
    return diag;
  };
 
  for (auto op : classes) {
    if (op == classOp)
      continue;
 
    if (classOp.getBodyBlock()->getNumArguments() !=
        op.getBodyBlock()->getNumArguments())
      return emitError(op) << "the number of arguments is not equal, "
                           << classOp.getBodyBlock()->getNumArguments()
                           << " vs " << op.getBodyBlock()->getNumArguments();
    unsigned index = 0;
    for (auto [l, r] : llvm::zip(classOp.getBodyBlock()->getArgumentTypes(),
                                 op.getBodyBlock()->getArgumentTypes())) {
      if (l != r)
        return emitError(op) << index << "-th argument type is not equal, " << l
                             << " vs " << r;
      index++;
    }
    // Check declared fields.
    llvm::DenseSet<StringAttr> declaredFields;
 
    for (auto nameAttr : op.getFieldNames()) {
      StringAttr name = cast<StringAttr>(nameAttr);
      std::optional<Type> opTypeOpt = op.getFieldType(name);
 
      if (!opTypeOpt.has_value())
        return emitError(op) << " no type for field " << name;
      Type opType = opTypeOpt.value();
 
      std::optional<Type> classTypeOpt = classOp.getFieldType(name);
 
      // Field not found in its definition.
      if (!classTypeOpt.has_value())
        return emitError(op) << "declaration has a field " << name
                             << " but not found in its definition";
      Type classType = classTypeOpt.value();
 
      if (classType != opType)
        return emitError(op)
               << "declaration has a field " << name
               << " but types don't match, " << classType << " vs " << opType;
      declaredFields.insert(name);
    }
 
    for (auto fieldName : classOp.getFieldNames())
      if (!declaredFields.count(cast<StringAttr>(fieldName)))
        return emitError(op) << "definition has a field " << fieldName
                             << " but not found in this declaration";
  }
  return false;
}
 
void LinkModulesPass::runOnOperation() {
  auto toplevelModule = getOperation();
  // 1. Initialize ModuleInfo.
  SmallVector<ModuleInfo> modules;
  size_t counter = 0;
  for (auto module : toplevelModule.getOps<ModuleOp>()) {
    auto name = module->getAttrOfType<StringAttr>("om.namespace");
    // Use `counter` if the namespace is not specified beforehand.
    if (!name) {
      name = StringAttr::get(module.getContext(), "module_" + Twine(counter++));
      module->setAttr("om.namespace", name);
    }
    modules.emplace_back(module);
  }
 
  if (failed(failableParallelForEach(&getContext(), modules, [](auto &info) {
        // Collect local information.
        return info.initialize();
      })))
    return signalPassFailure();
 
  // 2. Symbol resolution. Check that there is exactly single definition for
  //    public symbols and rename private symbols if necessary.
 
  // Global namespace to get unique names to symbols.
  Namespace nameSpace;
  // A map from a pair of enclosing module op and old symbol to a new symbol.
  SymMappingTy symMapping;
 
  // Construct a global map from symbols to class operations.
  llvm::MapVector<StringAttr, SmallVector<ClassLike>> symbolToClasses;
  for (const auto &info : modules)
    for (auto &[name, op] : info.symbolToClasses) {
      symbolToClasses[name].push_back(op);
      // Add names to avoid collision.
      (void)nameSpace.newName(name.getValue());
    }
 
  // Resolve symbols. We consider a symbol used as an external module to be
  // "public" thus we cannot rename such symbols when there is collision. We
  // require a public symbol to have exactly one definition so otherwise raise
  // an error.
  for (auto &[name, classes] : symbolToClasses) {
    // Check if it's legal to link classes. `resolveClasses` returns true if
    // it's necessary to rename symbols.
    auto result = resolveClasses(name, classes);
    if (failed(result))
      return signalPassFailure();
 
    // We can resolve symbol collision for symbols not referred by external
    // classes. Create a new name using `om.namespace` attributes as a
    // suffix.
    if (*result)
      for (auto op : classes) {
        auto enclosingModule = cast<mlir::ModuleOp>(op->getParentOp());
        auto nameSpaceId =
            enclosingModule->getAttrOfType<StringAttr>("om.namespace");
        symMapping[{enclosingModule, name}] = StringAttr::get(
            &getContext(),
            nameSpace.newName(name.getValue(), nameSpaceId.getValue()));
      }
  }
 
  // 3. Post-processing. Update class names and erase external classes.
 
  // Rename private symbols and remove external classes.
  parallelForEach(&getContext(), modules,
                  [&](auto &info) { info.postProcess(symMapping); });
 
  // Finally move operations to the toplevel module.
  auto *block = toplevelModule.getBody();
  for (auto &info : modules) {
    block->getOperations().splice(block->end(),
                                  info.module.getBody()->getOperations());
    // Restore non-OM operations.
    assert(info.module.getBody()->empty());
    info.module.getBody()->getOperations().splice(
        info.module.getBody()->begin(), info.block->getOperations());
  }
}