[RemoteAST] Support for extracting the type/valuea out of an existential.

This will be used in lldb.
<rdar://problem/41546568>

Author: Davide Italiano

include/swift/Remote/MetadataReader.h

@@ -264,6 +264,14 @@ class MetadataReader {
     return start;
   }
 
+  /// Given a pointer to an address, attemp to read the pointed value.
+  llvm::Optional<StoredPointer> readPointedValue(StoredPointer Address) {
+    StoredPointer PointedVal;
+    if (!Reader->readInteger(RemoteAddress(Address), &PointedVal))
+      return llvm::None;
+    return llvm::Optional<StoredPointer>(PointedVal);
+  }
+
   /// Given a pointer to the metadata, attempt to read the value
   /// witness table. Note that it's not safe to access any non-mandatory
   /// members of the value witness table, like extra inhabitants or enum members.

include/swift/RemoteAST/RemoteAST.h

@@ -211,6 +211,14 @@ class RemoteASTContext {
   /// Given a heap object, resolve its heap metadata.
   Result<remote::RemoteAddress>
   getHeapMetadataForObject(remote::RemoteAddress address);
+
+  /// Given an existential and its static type, resolve its dynamic
+  /// type and address. A single step of unwrapping is performed, i.e. if the
+  /// value stored inside the existential is itself an existential, the
+  /// caller can decide whether to iterate itself.
+  Result<std::pair<Type, remote::RemoteAddress>>
+  getDynamicTypeAndAddressForExistential(remote::RemoteAddress address,
+                                         Type staticType);
 };
 
 } // end namespace remoteAST

lib/RemoteAST/RemoteAST.cpp

@@ -20,6 +20,7 @@
 #include "swift/Subsystems.h"
 #include "swift/AST/ASTContext.h"
 #include "swift/AST/Decl.h"
+#include "swift/AST/ExistentialLayout.h"
 #include "swift/AST/GenericSignature.h"
 #include "swift/AST/Module.h"
 #include "swift/AST/NameLookup.h"
@@ -810,6 +811,9 @@ class RemoteASTContextImpl {
   getDeclForRemoteNominalTypeDescriptor(RemoteAddress descriptor) = 0;
   virtual Result<RemoteAddress>
   getHeapMetadataForObject(RemoteAddress object) = 0;
+  virtual Result<std::pair<Type, RemoteAddress>>
+  getDynamicTypeAndAddressForExistential(RemoteAddress object,
+                                         Type staticType) = 0;
 
   Result<uint64_t>
   getOffsetOfMember(Type type, RemoteAddress optMetadata, StringRef memberName){
@@ -1162,6 +1166,85 @@ class RemoteASTContextConcreteImpl final : public RemoteASTContextImpl {
     if (result) return RemoteAddress(*result);
     return getFailure<RemoteAddress>();
   }
+
+  Result<std::pair<Type, RemoteAddress>>
+  getDynamicTypeAndAddressClassExistential(RemoteAddress object) {
+    auto pointed = Reader.readPointedValue(object.getAddressData());
+    if (!pointed)
+      return getFailure<std::pair<Type, RemoteAddress>>();
+    auto result = Reader.readMetadataFromInstance(*pointed);
+    if (!result)
+      return getFailure<std::pair<Type, RemoteAddress>>();
+    auto typeResult = Reader.readTypeFromMetadata(result.getValue());
+    if (!typeResult)
+      return getFailure<std::pair<Type, RemoteAddress>>();
+    return std::make_pair<Type, RemoteAddress>(std::move(typeResult),
+                                               std::move(object));
+  }
+
+  Result<std::pair<Type, RemoteAddress>>
+  getDynamicTypeAndAddressErrorExistential(RemoteAddress object) {
+    auto pointed = Reader.readPointedValue(object.getAddressData());
+    if (!pointed)
+      return getFailure<std::pair<Type, RemoteAddress>>();
+    auto result =
+        Reader.readMetadataAndValueErrorExistential(RemoteAddress(*pointed));
+    if (!result)
+      return getFailure<std::pair<Type, RemoteAddress>>();
+    RemoteAddress metadataAddress = result->first;
+    RemoteAddress valueAddress = result->second;
+
+    auto typeResult =
+        Reader.readTypeFromMetadata(metadataAddress.getAddressData());
+    if (!typeResult)
+      return getFailure<std::pair<Type, RemoteAddress>>();
+    return std::make_pair<Type, RemoteAddress>(std::move(typeResult),
+                                               std::move(valueAddress));
+  }
+
+  Result<std::pair<Type, RemoteAddress>>
+  getDynamicTypeAndAddressOpaqueExistential(RemoteAddress object) {
+    auto result = Reader.readMetadataAndValueOpaqueExistential(object);
+    if (!result)
+      return getFailure<std::pair<Type, RemoteAddress>>();
+    RemoteAddress metadataAddress = result->first;
+    RemoteAddress valueAddress = result->second;
+
+    auto typeResult =
+        Reader.readTypeFromMetadata(metadataAddress.getAddressData());
+    if (!typeResult)
+      return getFailure<std::pair<Type, RemoteAddress>>();
+    return std::make_pair<Type, RemoteAddress>(std::move(typeResult),
+                                               std::move(valueAddress));
+  }
+
+  /// Resolve the dynamic type and the value address of an existential,
+  /// given its address and its static type. For class and error existentials,
+  /// this API takes a pointer to the instance reference rather than the
+  /// instance reference itself.
+  Result<std::pair<Type, RemoteAddress>>
+  getDynamicTypeAndAddressForExistential(RemoteAddress object,
+                                         Type staticType) override {
+    // If this is not an existential, give up.
+    if (!staticType->isAnyExistentialType())
+      return getFailure<std::pair<Type, RemoteAddress>>();
+
+    // TODO: implement support for ExistentialMetaTypes.
+    if (!staticType->isExistentialType())
+      return getFailure<std::pair<Type, RemoteAddress>>();
+
+    // This should be an existential type at this point.
+    auto layout = staticType->getExistentialLayout();
+    switch (layout.getKind()) {
+    case ExistentialLayout::Kind::Class:
+      return getDynamicTypeAndAddressClassExistential(object);
+    case ExistentialLayout::Kind::Error:
+      return getDynamicTypeAndAddressErrorExistential(object);
+    case ExistentialLayout::Kind::Opaque:
+      return getDynamicTypeAndAddressOpaqueExistential(object);
+    }
+    llvm_unreachable("invalid type kind");
+  }
 };
 
 } // end anonymous namespace
@@ -1219,3 +1302,10 @@ Result<remote::RemoteAddress>
 RemoteASTContext::getHeapMetadataForObject(remote::RemoteAddress address) {
   return asImpl(Impl)->getHeapMetadataForObject(address);
 }
+
+Result<std::pair<Type, remote::RemoteAddress>>
+RemoteASTContext::getDynamicTypeAndAddressForExistential(
+    remote::RemoteAddress address, Type staticType) {
+  return asImpl(Impl)->getDynamicTypeAndAddressForExistential(address,
+                                                              staticType);
+}

test/RemoteAST/existentials.swift

@@ -0,0 +1,46 @@
+// RUN: %target-swift-remoteast-test %s | %FileCheck %s
+
+// REQUIRES: swift-remoteast-test
+
+@_silgen_name("printDynamicTypeAndAddressForExistential")
+func printDynamicTypeAndAddressForExistential<T>(_: T)
+
+struct MyStruct<T, U, V> {
+  let x: T
+  let y: U
+  let z: V
+}
+
+// Case one, small opaque (fits into the inline buffer).
+// CHECK: MyStruct<Int, Int, Int>
+let smallStruct = MyStruct(x : 1, y: 2, z: 3)
+printDynamicTypeAndAddressForExistential(smallStruct as Any)
+
+// Case two, large opaque (boxed representation).
+// CHECK-NEXT: MyStruct<(Int, Int, Int), (Int, Int, Int), (Int, Int, Int)>
+let largeStruct = MyStruct(x: (1,1,1), y: (2,2,2), z: (3,3,3))
+printDynamicTypeAndAddressForExistential(largeStruct as Any)
+
+class MyClass<T, U> {
+  let x: T
+  let y: (T, U)
+  init(x: T, y: (T, U)) {
+    self.x = x
+    self.y = y
+  }
+}
+
+// Case three, class existential (adheres to AnyObject protocol).a
+// CHECK-NEXT: MyClass<Int, Int>
+let mc = MyClass(x : 23, y : (42, 44)) as AnyObject
+printDynamicTypeAndAddressForExistential(mc)
+
+enum MyError : Error {
+    case a
+    case b
+}
+
+// Case four: error existential.
+// CHECK-NEXT: MyError
+let q : Error  = MyError.a
+printDynamicTypeAndAddressForExistential(q)

tools/swift-remoteast-test/swift-remoteast-test.cpp

@@ -21,6 +21,7 @@
 #include "swift/Basic/LLVM.h"
 #include "swift/Basic/LLVMInitialize.h"
 #include "llvm/ADT/SmallVector.h"
+#include "llvm/Support/Format.h"
 #include "llvm/Support/raw_ostream.h"
 #include <cassert>
 
@@ -141,6 +142,39 @@ extern "C" void printTypeMetadataMemberOffset(const Metadata *typeMetadata,
   printMemberOffset(typeMetadata, memberName, /*pass metadata*/ true);
 }
 
+// FIXME: swiftcall
+/// func printDynamicTypeAndAddressForExistential<T>(_: T)
+LLVM_ATTRIBUTE_USED SWIFT_REMOTEAST_TEST_ABI extern "C" void
+printDynamicTypeAndAddressForExistential(void *object,
+                                         const Metadata *typeMetadata) {
+  assert(Context && "context was not set");
+  std::shared_ptr<MemoryReader> reader(new InProcessMemoryReader());
+  RemoteASTContext remoteAST(*Context, std::move(reader));
+
+  auto &out = llvm::outs();
+
+  // First, retrieve the static type of the existential, so we can understand
+  // which kind of existential this is.
+  auto staticTypeResult =
+      remoteAST.getTypeForRemoteTypeMetadata(RemoteAddress(typeMetadata));
+  if (!staticTypeResult) {
+    out << "failed to resolve static type: "
+        << staticTypeResult.getFailure().render() << '\n';
+    return;
+  }
+
+  // OK, we can reconstruct the dynamic type and the address now.
+  auto result = remoteAST.getDynamicTypeAndAddressForExistential(
+      RemoteAddress(object), staticTypeResult.getValue());
+  if (result) {
+    out << "found type: ";
+    result.getValue().first.print(out);
+    out << "\n";
+  } else {
+    out << result.getFailure().render() << '\n';
+  }
+}
+
 namespace {
 
 struct Observer : public FrontendObserver {