[NFC] Move generic contexts and metadata references into separate headers

Author: rjmccall

include/swift/ABI/GenericContext.h

@@ -0,0 +1,380 @@
+//===--- GenericContext.h - ABI for generic signatures ----------*- C++ -*-===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2022 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
+//
+//===----------------------------------------------------------------------===//
+//
+// This file describes runtime metadata structures for representing
+// generic signatures.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef SWIFT_ABI_GENERICCONTEXT_H
+#define SWIFT_ABI_GENERICCONTEXT_H
+
+#include "swift/ABI/TargetLayout.h"
+#include "swift/ABI/MetadataValues.h"
+#include "swift/ABI/MetadataRef.h"
+#include "swift/ABI/TrailingObjects.h"
+#include "swift/Demangling/Demangle.h"
+
+namespace swift {
+template <typename Runtime>
+struct TargetProtocolConformanceDescriptor;
+template <typename Runtime>
+struct TargetGenericContext;
+
+template <typename Runtime>
+struct TargetGenericContextDescriptorHeader {
+  /// The number of (source-written) generic parameters, and thus
+  /// the number of GenericParamDescriptors associated with this
+  /// context.  The parameter descriptors appear in the order in
+  /// which they were given in the source.
+  ///
+  /// A GenericParamDescriptor corresponds to a type metadata pointer
+  /// in the arguments layout when isKeyArgument() is true.
+  /// isKeyArgument() will be false if the parameter has been unified
+  /// unified with a different parameter or an associated type.
+  uint16_t NumParams;
+
+  /// The number of GenericRequirementDescriptors in this generic
+  /// signature.
+  ///
+  /// A GenericRequirementDescriptor of kind Protocol corresponds
+  /// to a witness table pointer in the arguments layout when
+  /// isKeyArgument() is true.  isKeyArgument() will be false if
+  /// the protocol is an Objective-C protocol.  (Unlike generic
+  /// parameters, redundant conformance requirements can simply be
+  /// eliminated, and so that case is not impossible.)
+  uint16_t NumRequirements;
+
+  /// The size of the "key" area of the argument layout, in words.
+  /// Key arguments include generic parameters and conformance
+  /// requirements which are part of the identity of the context.
+  ///
+  /// The key area of the argument layout considers of a sequence
+  /// of type metadata pointers (in the same order as the parameter
+  /// descriptors, for those parameters which satisfy hasKeyArgument())
+  /// followed by a sequence of witness table pointers (in the same
+  /// order as the requirements, for those requirements which satisfy
+  /// hasKeyArgument()).
+  uint16_t NumKeyArguments;
+
+  /// In principle, the size of the "extra" area of the argument
+  /// layout, in words.  The idea was that extra arguments would
+  /// include generic parameters and conformances that are not part
+  /// of the identity of the context; however, it's unclear why we
+  /// would ever want such a thing.  As a result, this section is
+  /// unused, and this field is always zero.  It can be repurposed
+  /// as long as it remains zero in code which must be compatible
+  /// with existing Swift runtimes.
+  uint16_t NumExtraArguments;
+  
+  uint32_t getNumArguments() const {
+    return NumKeyArguments + NumExtraArguments;
+  }
+
+  /// Return the total size of the argument layout, in words.
+  /// The alignment of the argument layout is the word alignment.
+  uint32_t getArgumentLayoutSizeInWords() const {
+    return getNumArguments();
+  }
+
+  bool hasArguments() const {
+    return getNumArguments() > 0;
+  }
+};
+using GenericContextDescriptorHeader =
+  TargetGenericContextDescriptorHeader<InProcess>;
+
+template<typename Runtime>
+class TargetGenericRequirementDescriptor {
+public:
+  GenericRequirementFlags Flags;
+
+  /// The type that's constrained, described as a mangled name.
+  RelativeDirectPointer<const char, /*nullable*/ false> Param;
+
+  union {
+    /// A mangled representation of the same-type or base class the param is
+    /// constrained to.
+    ///
+    /// Only valid if the requirement has SameType or BaseClass kind.
+    RelativeDirectPointer<const char, /*nullable*/ false> Type;
+    
+    /// The protocol the param is constrained to.
+    ///
+    /// Only valid if the requirement has Protocol kind.
+    RelativeTargetProtocolDescriptorPointer<Runtime> Protocol;
+    
+    /// The conformance the param is constrained to use.
+    ///
+    /// Only valid if the requirement has SameConformance kind.
+    RelativeIndirectablePointer<TargetProtocolConformanceDescriptor<Runtime>,
+                                /*nullable*/ false> Conformance;
+    
+    /// The kind of layout constraint.
+    ///
+    /// Only valid if the requirement has Layout kind.
+    GenericRequirementLayoutKind Layout;
+  };
+
+  constexpr GenericRequirementFlags getFlags() const {
+    return Flags;
+  }
+
+  constexpr GenericRequirementKind getKind() const {
+    return getFlags().getKind();
+  }
+
+  /// Retrieve the generic parameter that is the subject of this requirement,
+  /// as a mangled type name.
+  llvm::StringRef getParam() const {
+    return swift::Demangle::makeSymbolicMangledNameStringRef(Param.get());
+  }
+
+  /// Retrieve the protocol for a Protocol requirement.
+  TargetProtocolDescriptorRef<Runtime> getProtocol() const {
+    assert(getKind() == GenericRequirementKind::Protocol);
+    return Protocol;
+  }
+
+  /// Retrieve the right-hand type for a SameType or BaseClass requirement.
+  llvm::StringRef getMangledTypeName() const {
+    assert(getKind() == GenericRequirementKind::SameType ||
+           getKind() == GenericRequirementKind::BaseClass);
+    return swift::Demangle::makeSymbolicMangledNameStringRef(Type.get());
+  }
+
+  /// Retrieve the protocol conformance record for a SameConformance
+  /// requirement.
+  const TargetProtocolConformanceDescriptor<Runtime> *getConformance() const {
+    assert(getKind() == GenericRequirementKind::SameConformance);
+    return Conformance;
+  }
+
+  /// Retrieve the layout constraint.
+  GenericRequirementLayoutKind getLayout() const {
+    assert(getKind() == GenericRequirementKind::Layout);
+    return Layout;
+  }
+
+  /// Determine whether this generic requirement has a known kind.
+  ///
+  /// \returns \c false for any future generic requirement kinds.
+  bool hasKnownKind() const {
+    switch (getKind()) {
+    case GenericRequirementKind::BaseClass:
+    case GenericRequirementKind::Layout:
+    case GenericRequirementKind::Protocol:
+    case GenericRequirementKind::SameConformance:
+    case GenericRequirementKind::SameType:
+      return true;
+    }
+
+    return false;
+  }
+};
+using GenericRequirementDescriptor =
+  TargetGenericRequirementDescriptor<InProcess>;
+
+template<typename Runtime>
+class TargetGenericEnvironment
+    : public swift::ABI::TrailingObjects<TargetGenericEnvironment<Runtime>,
+               uint16_t, GenericParamDescriptor,
+               TargetGenericRequirementDescriptor<Runtime>> {
+  using GenericRequirementDescriptor =
+    TargetGenericRequirementDescriptor<Runtime>;
+  using TrailingObjects =
+     swift::ABI::TrailingObjects<TargetGenericEnvironment<Runtime>,
+       uint16_t, GenericParamDescriptor, GenericRequirementDescriptor>;
+  friend TrailingObjects;
+
+#if !defined(_MSC_VER) || _MSC_VER >= 1920
+  template<typename T>
+  using OverloadToken = typename TrailingObjects::template OverloadToken<T>;
+#else
+// MSVC 2017 trips parsing an using of an using, of a variadic template
+#define OverloadToken typename TrailingObjects::template OverloadToken
+#endif
+
+  size_t numTrailingObjects(OverloadToken<uint16_t>) const {
+    return Flags.getNumGenericParameterLevels();
+  }
+
+  size_t numTrailingObjects(OverloadToken<GenericParamDescriptor>) const {
+    return getGenericParameterCounts().back();
+  }
+
+  size_t numTrailingObjects(OverloadToken<GenericRequirementDescriptor>) const {
+    return Flags.getNumGenericRequirements();
+  }
+
+#if defined(_MSC_VER) && _MSC_VER < 1920
+#undef OverloadToken
+#endif
+
+  GenericEnvironmentFlags Flags;
+
+public:
+  /// Retrieve the cumulative generic parameter counts at each level of genericity.
+  llvm::ArrayRef<uint16_t> getGenericParameterCounts() const {
+    return llvm::makeArrayRef(this->template getTrailingObjects<uint16_t>(),
+                              Flags.getNumGenericParameterLevels());
+  }
+
+  /// Retrieve the generic parameters descriptors.
+  llvm::ArrayRef<GenericParamDescriptor> getGenericParameters() const {
+    return llvm::makeArrayRef(
+        this->template getTrailingObjects<GenericParamDescriptor>(),
+        getGenericParameterCounts().back());
+  }
+
+  /// Retrieve the generic requirements.
+  llvm::ArrayRef<GenericRequirementDescriptor> getGenericRequirements() const {
+    return llvm::makeArrayRef(
+        this->template getTrailingObjects<GenericRequirementDescriptor>(),
+        Flags.getNumGenericRequirements());
+  }
+};
+
+using GenericEnvironmentDescriptor = TargetGenericEnvironment<InProcess>;
+
+/// CRTP class for a context descriptor that includes trailing generic
+/// context description.
+template<class Self,
+         template <typename> class TargetGenericContextHeaderType =
+           TargetGenericContextDescriptorHeader,
+         typename... FollowingTrailingObjects>
+class TrailingGenericContextObjects;
+
+// This oddity with partial specialization is necessary to get
+// reasonable-looking code while also working around various kinds of
+// compiler bad behavior with injected class names.
+template<class Runtime,
+         template <typename> class TargetSelf,
+         template <typename> class TargetGenericContextHeaderType,
+         typename... FollowingTrailingObjects>
+class TrailingGenericContextObjects<TargetSelf<Runtime>,
+                                    TargetGenericContextHeaderType,
+                                    FollowingTrailingObjects...> :
+  protected swift::ABI::TrailingObjects<TargetSelf<Runtime>,
+      TargetGenericContextHeaderType<Runtime>,
+      GenericParamDescriptor,
+      TargetGenericRequirementDescriptor<Runtime>,
+      FollowingTrailingObjects...>
+{
+protected:
+  using Self = TargetSelf<Runtime>;
+  using GenericContextHeaderType = TargetGenericContextHeaderType<Runtime>;
+  using GenericRequirementDescriptor =
+    TargetGenericRequirementDescriptor<Runtime>;
+
+  using TrailingObjects = swift::ABI::TrailingObjects<Self,
+    GenericContextHeaderType,
+    GenericParamDescriptor,
+    GenericRequirementDescriptor,
+    FollowingTrailingObjects...>;
+  friend TrailingObjects;
+
+#if !defined(_MSC_VER) || _MSC_VER >= 1920
+  template<typename T>
+  using OverloadToken = typename TrailingObjects::template OverloadToken<T>;
+#else
+// MSVC 2017 trips parsing an using of an using, of a variadic template
+#define OverloadToken typename TrailingObjects::template OverloadToken
+#endif
+  
+  const Self *asSelf() const {
+    return static_cast<const Self *>(this);
+  }
+public:
+  using StoredSize = typename Runtime::StoredSize;
+  using StoredPointer = typename Runtime::StoredPointer;
+
+  const GenericContextHeaderType &getFullGenericContextHeader() const {
+    assert(asSelf()->isGeneric());
+    return *this->template getTrailingObjects<GenericContextHeaderType>();
+  }
+
+  const TargetGenericContextDescriptorHeader<Runtime> &
+  getGenericContextHeader() const {
+    /// HeaderType ought to be convertible to GenericContextDescriptorHeader.
+    return getFullGenericContextHeader();
+  }
+  
+  const TargetGenericContext<Runtime> *getGenericContext() const {
+    if (!asSelf()->isGeneric())
+      return nullptr;
+    // The generic context header should always be immediately followed in
+    // memory by trailing parameter and requirement descriptors.
+    auto *header = reinterpret_cast<const char *>(&getGenericContextHeader());
+    return reinterpret_cast<const TargetGenericContext<Runtime> *>(
+      header - sizeof(TargetGenericContext<Runtime>));
+  }
+
+  llvm::ArrayRef<GenericParamDescriptor> getGenericParams() const {
+    if (!asSelf()->isGeneric())
+      return {};
+
+    return {this->template getTrailingObjects<GenericParamDescriptor>(),
+            getGenericContextHeader().NumParams};
+  }
+  
+  llvm::ArrayRef<GenericRequirementDescriptor> getGenericRequirements() const {
+    if (!asSelf()->isGeneric())
+      return {};
+    return {this->template getTrailingObjects<GenericRequirementDescriptor>(),
+            getGenericContextHeader().NumRequirements};
+  }
+
+  /// Return the amount of space that the generic arguments take up in
+  /// metadata of this type.
+  StoredSize getGenericArgumentsStorageSize() const {
+    return StoredSize(getGenericContextHeader().getNumArguments())
+             * sizeof(StoredPointer);
+  }
+
+protected:
+  size_t numTrailingObjects(OverloadToken<GenericContextHeaderType>) const {
+    return asSelf()->isGeneric() ? 1 : 0;
+  }
+  
+  size_t numTrailingObjects(OverloadToken<GenericParamDescriptor>) const {
+    return asSelf()->isGeneric() ? getGenericContextHeader().NumParams : 0;
+  }
+
+  size_t numTrailingObjects(OverloadToken<GenericRequirementDescriptor>) const {
+    return asSelf()->isGeneric() ? getGenericContextHeader().NumRequirements : 0;
+  }
+
+#if defined(_MSC_VER) && _MSC_VER < 1920
+#undef OverloadToken
+#endif
+
+};
+
+/// Description of a generic context.
+template<typename Runtime>
+struct TargetGenericContext final
+  : TrailingGenericContextObjects<TargetGenericContext<Runtime>,
+                                  TargetGenericContextDescriptorHeader>
+{
+  // This struct is supposed to be empty, but TrailingObjects respects the
+  // unique-address-per-object C++ rule, so even if this type is empty, the
+  // trailing objects will come after one byte of padding. This dummy field
+  // takes up space to make the offset of the trailing objects portable.
+  unsigned _dummy;
+
+  bool isGeneric() const { return true; }
+};
+
+} // end namespace swift
+
+#endif