GotoSolver.cpp

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//====- GotoSolver.cpp -----------------------------------===//
//
// 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 "PassDetail.h"
#include "clang/CIR/Dialect/IR/CIRDialect.h"
#include "clang/CIR/Dialect/Passes.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/StringMap.h"
#include "llvm/ADT/StringSet.h"
#include "llvm/Support/TimeProfiler.h"
#include <memory>
 
using namespace mlir;
using namespace cir;
 
namespace mlir {
#define GEN_PASS_DEF_GOTOSOLVER
#include "clang/CIR/Dialect/Passes.h.inc"
} // namespace mlir
 
namespace {
 
struct GotoSolverPass : public impl::GotoSolverBase<GotoSolverPass> {
  GotoSolverPass() = default;
  void runOnOperation() override;
};
 
static void process(cir::FuncOp func,
                    const llvm::StringSet<> &globalBlockAddrLabel) {
  mlir::OpBuilder rewriter(func.getContext());
  llvm::StringMap<Block *> labels;
  llvm::SmallVector<cir::GotoOp, 4> gotos;
  llvm::SmallSet<StringRef, 4> blockAddrLabel;
 
  func.getBody().walk([&](mlir::Operation *op) {
    if (auto lab = dyn_cast<cir::LabelOp>(op)) {
      labels.try_emplace(lab.getLabel(), lab->getBlock());
    } else if (auto goTo = dyn_cast<cir::GotoOp>(op)) {
      gotos.push_back(goTo);
    } else if (auto blockAddr = dyn_cast<cir::BlockAddressOp>(op)) {
      blockAddrLabel.insert(blockAddr.getBlockAddrInfo().getLabel());
    }
  });
 
  for (auto &lab : labels) {
    StringRef labelName = lab.getKey();
    Block *block = lab.getValue();
    // Keep labels whose address is taken either by a cir.block_address op in
    // this function or by a block-address attribute used elsewhere (e.g. in a
    // global initializer).
    if (!blockAddrLabel.contains(labelName) &&
        !globalBlockAddrLabel.contains(labelName)) {
      // erase the LabelOp inside the block if safe
      if (auto lab = dyn_cast<cir::LabelOp>(&block->front())) {
        lab.erase();
      }
    }
  }
 
  for (auto goTo : gotos) {
    mlir::OpBuilder::InsertionGuard guard(rewriter);
    rewriter.setInsertionPoint(goTo);
    Block *dest = labels[goTo.getLabel()];
    cir::BrOp::create(rewriter, goTo.getLoc(), dest);
    goTo.erase();
  }
}
 
void GotoSolverPass::runOnOperation() {
  llvm::TimeTraceScope scope("Goto Solver");
 
  // Block addresses can also appear in attributes outside of any function body,
  // such as global variable initializers. Collect, per target function, the
  // labels referenced this way so their LabelOps are not erased below.
  llvm::StringMap<llvm::StringSet<>> globalBlockAddrLabels;
  getOperation()->walk([&](mlir::Operation *op) {
    for (const mlir::NamedAttribute &namedAttr : op->getAttrs()) {
      namedAttr.getValue().walk([&](cir::BlockAddrInfoAttr info) {
        globalBlockAddrLabels[info.getFunc().getValue()].insert(
            info.getLabel());
      });
    }
  });
 
  static const llvm::StringSet<> emptySet;
  getOperation()->walk([&](cir::FuncOp func) {
    auto it = globalBlockAddrLabels.find(func.getSymName());
    process(func, it == globalBlockAddrLabels.end() ? emptySet : it->second);
  });
}
 
} // namespace
 
std::unique_ptr<Pass> mlir::createGotoSolverPass() {
  return std::make_unique<GotoSolverPass>();
}