//===--- PruneVTables.cpp - Prune unnecessary vtable entries --------------===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
// Mark sil_vtable entries as [nonoverridden] when possible, so that we know
// at IRGen time they can be elided from runtime vtables.
//
//===----------------------------------------------------------------------===//

#define DEBUG_TYPE "prune-vtables"

#include "swift/SILOptimizer/PassManager/Transforms.h"
#include "swift/SILOptimizer/Utils/InstOptUtils.h"

using namespace swift;

namespace {
class PruneVTables : public SILModuleTransform {
  void runOnVTable(SILModule *M,
                   SILVTable *vtable) {
    for (auto &entry : vtable->getMutableEntries()) {
      // We don't need to worry about entries that are inherited, overridden,
      // or have already been found to have no overrides.
      if (entry.TheKind != SILVTable::Entry::Normal) {
        continue;
      }
      
      // The destructor entry must remain.
      if (entry.Method.kind == SILDeclRef::Kind::Deallocator) {
        continue;
      }
      
      auto methodDecl = entry.Method.getAbstractFunctionDecl();
      if (!methodDecl)
        continue;

      // Is the method declared final?
      if (!methodDecl->isFinal()) {
        // Are callees of this entry statically knowable?
        if (!calleesAreStaticallyKnowable(*M, entry.Method))
          continue;
        
        // Does the method have any overrides in this module?
        if (methodDecl->isOverridden())
          continue;
      }
      
      entry.TheKind = SILVTable::Entry::NormalNonOverridden;
    }
  }
  
  void run() override {
    SILModule *M = getModule();
    
    for (auto &vtable : M->getVTables()) {
      runOnVTable(M, vtable);
    }
  }
};
}

SILTransform *swift::createPruneVTables() {
  return new PruneVTables();
}