LowerUniqueLabelsPass.cpp

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//===- LowerUniqueLabelsPass.cpp - RTG LowerUniqueLabelsPass impl. --------===//
//
// 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 label_unique_decl operations to label_decl operations by
// creating a unique label string based on all the existing unique and
// non-unique label declarations in the module.
//
//===----------------------------------------------------------------------===//
 
#include "circt/Dialect/RTG/IR/RTGOps.h"
#include "circt/Dialect/RTG/Transforms/RTGPasses.h"
#include "circt/Support/Namespace.h"
#include "mlir/IR/PatternMatch.h"
 
namespace circt {
namespace rtg {
#define GEN_PASS_DEF_LOWERUNIQUELABELSPASS
#include "circt/Dialect/RTG/Transforms/RTGPasses.h.inc"
} // namespace rtg
} // namespace circt
 
using namespace mlir;
using namespace circt;
using namespace circt::rtg;
 
//===----------------------------------------------------------------------===//
// Lower Unique Labels Pass
//===----------------------------------------------------------------------===//
 
namespace {
struct LowerUniqueLabelsPass
    : public rtg::impl::LowerUniqueLabelsPassBase<LowerUniqueLabelsPass> {
  using Base::Base;
 
  void runOnOperation() override;
};
} // namespace
 
static StringAttr getLabelName(LabelUniqueDeclOp op) {
  if (auto constOp = op.getNamePrefix().getDefiningOp<ConstantOp>())
    return dyn_cast<StringAttr>(constOp.getValue());
 
  op->emitError("label_unique_decl name prefix must be a constant string");
  return {};
}
 
void LowerUniqueLabelsPass::runOnOperation() {
  Namespace labelNames;
 
  // Collect all the label names in a first iteration.
  auto result = getOperation()->walk([&](Operation *op) -> WalkResult {
    if (isa<StringToLabelOp>(op))
      return op->emitError(
          "string_to_label operations must be elaborated before "
          "lowering unique labels");
 
    if (auto constOp = dyn_cast<ConstantOp>(op)) {
      if (auto labelAttr = dyn_cast<LabelAttr>(constOp.getValue()))
        labelNames.add(labelAttr.getName());
    } else if (auto labelDecl = dyn_cast<LabelUniqueDeclOp>(op)) {
      auto res = getLabelName(labelDecl);
      if (!res)
        return WalkResult::interrupt();
      labelNames.add(res);
    }
 
    return WalkResult::advance();
  });
 
  if (result.wasInterrupted())
    return signalPassFailure();
 
  // Lower the unique labels in a second iteration.
  getOperation()->walk([&](LabelUniqueDeclOp op) {
    // Convert 'rtg.label_unique_decl' to 'rtg.constant <labelAttr>' by
    // choosing a unique name based on the set of names we collected during
    // elaboration.
    IRRewriter rewriter(op);
    auto newName = labelNames.newName(getLabelName(op).getValue());
    rewriter.replaceOpWithNewOp<ConstantOp>(
        op, LabelAttr::get(rewriter.getContext(), newName));
    ++numLabelsLowered;
  });
}