SimplifyUnreachableContainingBlocks.cpp

//===--- SimplifyUnreachableContainingBlocks.cpp --------------------------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2017 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See https://swift.org/LICENSE.txt for license information
// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//
///
/// \file
///
/// This file contains a simple utility pass that simplifies blocks that contain
/// unreachables by eliminating all other instructions. This includes
/// instructions with side-effects and no-return functions. It is only intended
/// to be used to simplify IR for testing or exploratory purposes.
///
//===----------------------------------------------------------------------===//

#include "swift/SILOptimizer/PassManager/Passes.h"
#include "swift/SIL/SILBasicBlock.h"
#include "swift/SILOptimizer/PassManager/Transforms.h"

using namespace swift;

namespace {

class SimplifyUnreachableContainingBlocks : public SILFunctionTransform {
  void run() override {
    // For each block...
    for (auto &BB : *getFunction()) {
      // If the block does not contain an unreachable, just continue. There is
      // no further work to do.
      auto *UI = dyn_cast<UnreachableInst>(BB.getTerminator());
      if (!UI)
        continue;

      // Otherwise, eliminate all other instructions in the block.
      for (auto II = BB.begin(); &*II != UI;) {
        // Avoid iterator invalidation.
        auto *I = &*II;
        ++II;

        I->replaceAllUsesOfAllResultsWithUndef();
        I->eraseFromParent();
      }
    }
  }
};

} // end anonymous namespace

//===----------------------------------------------------------------------===//
//                           Top Level Entry Point
//===----------------------------------------------------------------------===//

SILTransform *swift::createSimplifyUnreachableContainingBlocks() {
  return new SimplifyUnreachableContainingBlocks();
}