lib/SILOptimizer/Transforms/AssumeSingleThreaded.cpp

//===--- AssumeSingleThreaded.cpp - Assume single-threaded execution  -----===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
// Assume that user code is single-thread.
//
// Convert all reference counting operations into non-atomic ones.
//
// To get read of most atomic reference counting operations, the standard
// library should be compiled in this mode as well 
//
// This pass affects only reference counting operations resulting from SIL
// instructions. It wouldn't affect places in the runtime C++ code which
// hard-code calls to retain/release. We could take advantage of the Instruments
// instrumentation stubs to redirect calls from the runtime if it was
// significant, or else just build a single-threaded variant of the runtime.
//
//===----------------------------------------------------------------------===//

#include "swift/SILOptimizer/PassManager/Passes.h"
#include "swift/SIL/SILFunction.h"
#include "swift/SIL/SILInstruction.h"
#include "swift/SIL/SILModule.h"
#include "swift/SILOptimizer/Utils/Local.h"
#include "swift/SILOptimizer/PassManager/Transforms.h"
#include "llvm/Support/CommandLine.h"

using namespace swift;

namespace {
class AssumeSingleThreaded : public swift::SILFunctionTransform {
  /// The entry point to the transformation.
  void run() override {
    if (!getOptions().AssumeSingleThreaded)
      return;
    for (auto &BB : *getFunction()) {
      for (auto &I : BB) {
        if (auto RCInst = dyn_cast<RefCountingInst>(&I))
          RCInst->setNonAtomic();
      }
    }
    invalidateAnalysis(SILAnalysis::InvalidationKind::Instructions);
  }

};
} // end anonymous namespace


SILTransform *swift::createAssumeSingleThreaded() {
  return new AssumeSingleThreaded();
}