SILGen: Emit convenience initializers as allocating entry points.

And only dispatch designated inits by their allocating entry points. rdar://problem/29634243

Author: jckarter

include/swift/AST/Decl.h

@@ -6463,9 +6463,8 @@ class MissingMemberDecl : public Decl {
 
   static MissingMemberDecl *
   forInitializer(ASTContext &ctx, DeclContext *DC, DeclName name,
-                 bool hasNormalVTableEntry,
-                 bool hasAllocatingVTableEntry) {
-    unsigned entries = hasNormalVTableEntry + hasAllocatingVTableEntry;
+                 bool hasVTableEntry) {
+    unsigned entries = hasVTableEntry ? 1 : 0;
     return new (ctx) MissingMemberDecl(DC, name, entries, 0);
   }
 

include/swift/SIL/SILVTableVisitor.h

@@ -93,20 +93,12 @@ template <class T> class SILVTableVisitor {
   void maybeAddConstructor(ConstructorDecl *cd) {
     assert(!cd->hasClangNode());
 
-    // Required constructors (or overrides thereof) have their allocating entry
-    // point in the vtable.
-    if (cd->isRequired()) {
-      SILDeclRef constant(cd, SILDeclRef::Kind::Allocator);
-      maybeAddEntry(constant, constant.requiresNewVTableEntry());
-    }
-
-    // Designated and/or required initializers have their initializing
-    // constructor in the vtable, which can be used by a convenience
-    // initializer.
-    if (cd->isDesignatedInit() || cd->isRequired()) {
-      SILDeclRef constant(cd, SILDeclRef::Kind::Initializer);
-      maybeAddEntry(constant, constant.requiresNewVTableEntry());
-    }
+    // The allocating entry point is what is used for dynamic dispatch.
+    // The initializing entry point for designated initializers is only
+    // necessary for super.init chaining, which is sufficiently constrained
+    // to never need dynamic dispatch.
+    SILDeclRef constant(cd, SILDeclRef::Kind::Allocator);
+    maybeAddEntry(constant, constant.requiresNewVTableEntry());    
   }
 
   void maybeAddEntry(SILDeclRef declRef, bool needsNewEntry) {

lib/AST/Decl.cpp

@@ -5251,6 +5251,18 @@ static bool requiresNewVTableEntry(const AbstractFunctionDecl *decl) {
   // Dynamic methods are always accessed by objc_msgSend().
   if (decl->isFinal() || decl->isDynamic() || decl->hasClangNode())
     return false;
+  
+  // Initializers are not normally inherited, but required initializers can
+  // be overridden for invocation from dynamic types, and convenience initializers
+  // are conditionally inherited when all designated initializers are available,
+  // working by dynamically invoking the designated initializer implementation
+  // from the subclass. Convenience initializers can also override designated
+  // initializer implementations from their superclass.
+  if (auto ctor = dyn_cast<ConstructorDecl>(decl)) {
+    if (!ctor->isRequired() && !ctor->isDesignatedInit()) {
+      return false;
+    }
+  }
 
   if (auto *accessor = dyn_cast<AccessorDecl>(decl)) {
     // Check to see if it's one of the opaque accessors for the declaration.
@@ -5262,6 +5274,16 @@ static bool requiresNewVTableEntry(const AbstractFunctionDecl *decl) {
   auto base = decl->getOverriddenDecl();
   if (!base || base->hasClangNode() || base->isDynamic())
     return true;
+  
+  // As above, convenience initializers are not formally overridable in Swift
+  // vtables, although same-named initializers are modeled as overriding for
+  // various QoI and objc interop reasons. Even if we "override" a non-required
+  // convenience init, we still need a distinct vtable entry.
+  if (auto baseCtor = dyn_cast<ConstructorDecl>(base)) {
+    if (!baseCtor->isRequired() && !baseCtor->isDesignatedInit()) {
+      return true;
+    }
+  }
 
   // If the method overrides something, we only need a new entry if the
   // override has a more general AST type. However an abstraction

lib/SIL/SILDeclRef.cpp

@@ -48,20 +48,21 @@ swift::getMethodDispatch(AbstractFunctionDecl *method) {
     if (method->isFinal())
       return MethodDispatch::Static;
 
+    // Imported class methods are dynamically dispatched.
+    if (method->isObjC() && method->hasClangNode())
+      return MethodDispatch::Class;
+
     // Members defined directly inside a class are dynamically dispatched.
     if (isa<ClassDecl>(dc)) {
-      // Convenience initializers are not dynamically dispatched unless
+      // Native convenience initializers are not dynamically dispatched unless
       // required.
       if (auto ctor = dyn_cast<ConstructorDecl>(method)) {
-        if (!ctor->isRequired() && ctor->isConvenienceInit())
+        if (!ctor->isRequired() && !ctor->isDesignatedInit()
+            && !requiresForeignEntryPoint(ctor))
           return MethodDispatch::Static;
       }
       return MethodDispatch::Class;
     }
-
-    // Imported class methods are dynamically dispatched.
-    if (method->isObjC() && method->hasClangNode())
-      return MethodDispatch::Class;
   }
 
   // Otherwise, it can be referenced statically.
@@ -722,16 +723,6 @@ std::string SILDeclRef::mangle(ManglingKind MKind) const {
 bool SILDeclRef::requiresNewVTableEntry() const {
   if (cast<AbstractFunctionDecl>(getDecl())->needsNewVTableEntry())
     return true;
-  if (kind == SILDeclRef::Kind::Allocator) {
-    auto *cd = cast<ConstructorDecl>(getDecl());
-    if (cd->isRequired()) {
-      auto *baseCD = cd->getOverriddenDecl();
-      if(!baseCD ||
-         !baseCD->isRequired() ||
-         baseCD->hasClangNode())
-        return true;
-    }
-  }
   return false;
 }
 
@@ -755,18 +746,34 @@ SILDeclRef SILDeclRef::getOverridden() const {
 
 SILDeclRef SILDeclRef::getNextOverriddenVTableEntry() const {
   if (auto overridden = getOverridden()) {
-    // If we overrode a foreign decl, a dynamic method, this is an
+    // If we overrode a foreign decl or dynamic method, if this is an
     // accessor for a property that overrides an ObjC decl, or if it is an
     // @NSManaged property, then it won't be in the vtable.
     if (overridden.getDecl()->hasClangNode())
       return SILDeclRef();
-
-    // If we overrode a non-required initializer, there won't be a vtable
-    // slot for the allocator.
+    
+    // An @objc convenience initializer can be "overridden" in the sense that
+    // its selector is reclaimed by a subclass's convenience init with the
+    // same name. The AST models this as an override for the purposes of
+    // ObjC selector validation, but it isn't for Swift method dispatch
+    // purposes.
     if (overridden.kind == SILDeclRef::Kind::Allocator) {
-      if (!cast<ConstructorDecl>(overridden.getDecl())->isRequired())
+      auto overriddenCtor = cast<ConstructorDecl>(overridden.getDecl());
+      if (!overriddenCtor->isDesignatedInit()
+          && !overriddenCtor->isRequired())
         return SILDeclRef();
-    } else if (overridden.getDecl()->isDynamic()) {
+    }
+
+    // Initializing entry points for initializers won't be in the vtable.
+    // For Swift designated initializers, they're only used in super.init
+    // chains, which can always be statically resolved. Other native Swift
+    // initializers only have allocating entry points. ObjC initializers always
+    // have the initializing entry point (corresponding to the -init method)
+    // but those are never in the vtable.
+    if (overridden.kind == SILDeclRef::Kind::Initializer) {
+      return SILDeclRef();
+    }
+    if (overridden.getDecl()->isDynamic()) {
       return SILDeclRef();
     }
 

lib/SILGen/SILGen.cpp

@@ -757,37 +757,16 @@ void SILGenModule::emitConstructor(ConstructorDecl *decl) {
 
   bool ForCoverageMapping = doesASTRequireProfiling(M, decl);
 
-  if (declCtx->getSelfClassDecl()) {
-    // Class constructors have separate entry points for allocation and
-    // initialization.
+  auto emitClassAllocatorThunk = [&]{
     emitOrDelayFunction(
         *this, constant, [this, constant, decl](SILFunction *f) {
           preEmitFunction(constant, decl, f, decl);
           PrettyStackTraceSILFunction X("silgen emitConstructor", f);
           SILGenFunction(*this, *f, decl).emitClassConstructorAllocator(decl);
           postEmitFunction(constant, f);
         });
-
-    // Constructors may not have bodies if they've been imported, or if they've
-    // been parsed from a textual interface.
-    if (decl->hasBody()) {
-      SILDeclRef initConstant(decl, SILDeclRef::Kind::Initializer);
-      emitOrDelayFunction(
-          *this, initConstant,
-          [this, initConstant, decl, declCtx](SILFunction *initF) {
-            preEmitFunction(initConstant, decl, initF, decl);
-            PrettyStackTraceSILFunction X("silgen constructor initializer",
-                                          initF);
-            initF->setProfiler(
-                getOrCreateProfilerForConstructors(declCtx, decl));
-            SILGenFunction(*this, *initF, decl)
-              .emitClassConstructorInitializer(decl);
-            postEmitFunction(initConstant, initF);
-          },
-          /*forceEmission=*/ForCoverageMapping);
-    }
-  } else {
-    // Struct and enum constructors do everything in a single function.
+  };
+  auto emitValueConstructorIfHasBody = [&]{
     if (decl->hasBody()) {
       emitOrDelayFunction(
           *this, constant, [this, constant, decl, declCtx](SILFunction *f) {
@@ -798,6 +777,47 @@ void SILGenModule::emitConstructor(ConstructorDecl *decl) {
             postEmitFunction(constant, f);
           });
     }
+  };
+  
+  if (declCtx->getSelfClassDecl()) {
+    // Designated initializers for classes have have separate entry points for
+    // allocation and initialization.
+    if (decl->isDesignatedInit()) {
+      emitClassAllocatorThunk();
+
+      // Constructors may not have bodies if they've been imported, or if they've
+      // been parsed from a textual interface.
+      if (decl->hasBody()) {
+        SILDeclRef initConstant(decl, SILDeclRef::Kind::Initializer);
+        emitOrDelayFunction(
+            *this, initConstant,
+            [this, initConstant, decl, declCtx](SILFunction *initF) {
+              preEmitFunction(initConstant, decl, initF, decl);
+              PrettyStackTraceSILFunction X("silgen constructor initializer",
+                                            initF);
+              initF->setProfiler(
+                  getOrCreateProfilerForConstructors(declCtx, decl));
+              SILGenFunction(*this, *initF, decl)
+                .emitClassConstructorInitializer(decl);
+              postEmitFunction(initConstant, initF);
+            },
+            /*forceEmission=*/ForCoverageMapping);
+      }
+    // Convenience initializers for classes behave more like value constructors
+    // in that there's only an allocating entry point that effectively
+    // "constructs" the self reference by invoking another initializer.
+    } else {
+      emitValueConstructorIfHasBody();
+      
+      // If the convenience initializer was imported from ObjC, we still have to
+      // emit the allocator thunk.
+      if (decl->hasClangNode()) {
+        emitClassAllocatorThunk();
+      }
+    }
+  } else {
+    // Struct and enum constructors do everything in a single function.
+    emitValueConstructorIfHasBody();
   }
 }