LayerMerge.cpp

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//===- LayerMerge.cpp - Merge layer blocks together -----------------------===//
//
// 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 merges layer blocks in a module which reference the same layer
// definition.
//
//===----------------------------------------------------------------------===//
 
#include "circt/Dialect/FIRRTL/FIRRTLOps.h"
#include "circt/Dialect/FIRRTL/Passes.h"
#include "mlir/IR/Iterators.h"
#include "mlir/IR/PatternMatch.h"
#include "mlir/Pass/Pass.h"
#include "llvm/Support/Debug.h"
 
#define DEBUG_TYPE "firrtl-layer-merge"
 
namespace circt {
namespace firrtl {
#define GEN_PASS_DEF_LAYERMERGE
#include "circt/Dialect/FIRRTL/Passes.h.inc"
} // namespace firrtl
} // namespace circt
 
using namespace circt;
using namespace firrtl;
 
namespace {
/// A pass that merges layer blocks referencing the same layer definition.
struct LayerMerge : public circt::firrtl::impl::LayerMergeBase<LayerMerge> {
  void runOnOperation() override;
};
} // namespace
 
void LayerMerge::runOnOperation() {
  LLVM_DEBUG(
      llvm::dbgs() << "==----- Running LayerMerge "
                      "--------------------------------------------------===\n"
                   << "Module: '" << getOperation().getName() << "'\n";);
 
  // Track the last layer block in a module associated with a specific layer.
  llvm::DenseMap<SymbolRefAttr, LayerBlockOp> lastBlockMap;
 
  // Recursively visit LayerBlockOps in reverse order.  Merge all earlier layer
  // blocks into the last layer blocks of the same layer definition.
  //
  // The recursive walk will cause nested layer blocks to also be merged.
  auto moduleOp = getOperation();
  mlir::IRRewriter rewriter(moduleOp.getContext());
  moduleOp.walk<mlir::WalkOrder::PostOrder, mlir::ReverseIterator>(
      [&](LayerBlockOp thisBlock) {
        auto layer = thisBlock.getLayerName();
        // If we haven't seen this block before, then it is the last block.
        auto [item, inserted] = lastBlockMap.try_emplace(layer, thisBlock);
        if (inserted)
          return WalkResult::advance();
 
        auto &lastBlock = item->getSecond();
        rewriter.inlineBlockBefore(thisBlock.getBody(), lastBlock.getBody(),
                                   lastBlock.getBody()->begin());
        thisBlock->erase();
        numMerged++;
        return WalkResult::advance();
      });
}
 
std::unique_ptr<mlir::Pass> circt::firrtl::createLayerMergePass() {
  return std::make_unique<LayerMerge>();
}