Add llvm:Attribute::Returned to the weak runtime functions

rdar://18172130

Author: aschwaighofer

include/swift/Runtime/RuntimeFunctions.def

@@ -464,17 +464,17 @@ FUNCTION(NativeWeakDestroy, swift_weakDestroy, DefaultCC,
          ARGS(WeakReferencePtrTy),
          ATTRS(NoUnwind))
 
-// void swift_weakInit(WeakReference *object, void *value);
+// WeakReference *swift_weakInit(WeakReference *object, void *value);
 FUNCTION(NativeWeakInit, swift_weakInit, DefaultCC,
          RETURNS(WeakReferencePtrTy),
          ARGS(WeakReferencePtrTy, RefCountedPtrTy),
-         ATTRS(NoUnwind))
+         ATTRS(NoUnwind, FirstParamReturned))
 
-// void swift_weakAssign(WeakReference *object, void *value);
+// WeakReferencePtr *swift_weakAssign(WeakReference *object, void *value);
 FUNCTION(NativeWeakAssign, swift_weakAssign, DefaultCC,
          RETURNS(WeakReferencePtrTy),
          ARGS(WeakReferencePtrTy, RefCountedPtrTy),
-         ATTRS(NoUnwind))
+         ATTRS(NoUnwind, FirstParamReturned))
 
 // void *swift_weakLoadStrong(WeakReference *object);
 FUNCTION(NativeWeakLoadStrong, swift_weakLoadStrong,DefaultCC,
@@ -488,29 +488,29 @@ FUNCTION(NativeWeakTakeStrong, swift_weakTakeStrong,DefaultCC,
          ARGS(WeakReferencePtrTy),
          ATTRS(NoUnwind))
 
-// void swift_weakCopyInit(WeakReference *dest, WeakReference *src);
+// WeakReference *swift_weakCopyInit(WeakReference *dest, WeakReference *src);
 FUNCTION(NativeWeakCopyInit, swift_weakCopyInit, DefaultCC,
          RETURNS(WeakReferencePtrTy),
          ARGS(WeakReferencePtrTy, WeakReferencePtrTy),
-         ATTRS(NoUnwind))
+         ATTRS(NoUnwind, FirstParamReturned))
 
-// void swift_weakTakeInit(WeakReference *dest, WeakReference *src);
+// WeakReference *swift_weakTakeInit(WeakReference *dest, WeakReference *src);
 FUNCTION(NativeWeakTakeInit, swift_weakTakeInit, DefaultCC,
          RETURNS(WeakReferencePtrTy),
          ARGS(WeakReferencePtrTy, WeakReferencePtrTy),
-         ATTRS(NoUnwind))
+         ATTRS(NoUnwind, FirstParamReturned))
 
-// void swift_weakCopyAssign(WeakReference *dest, WeakReference *src);
+// WeakReference *swift_weakCopyAssign(WeakReference *dest, WeakReference *src);
 FUNCTION(NativeWeakCopyAssign, swift_weakCopyAssign, DefaultCC,
          RETURNS(WeakReferencePtrTy),
          ARGS(WeakReferencePtrTy, WeakReferencePtrTy),
-         ATTRS(NoUnwind))
+         ATTRS(NoUnwind, FirstParamReturned))
 
-// void swift_weakTakeAssign(WeakReference *dest, WeakReference *src);
+// WeakReference *swift_weakTakeAssign(WeakReference *dest, WeakReference *src);
 FUNCTION(NativeWeakTakeAssign, swift_weakTakeAssign, DefaultCC,
          RETURNS(WeakReferencePtrTy),
          ARGS(WeakReferencePtrTy, WeakReferencePtrTy),
-         ATTRS(NoUnwind))
+         ATTRS(NoUnwind, FirstParamReturned))
 
 // void swift_unknownWeakDestroy(WeakReference *object);
 FUNCTION(UnknownWeakDestroy, swift_unknownWeakDestroy, DefaultCC,

lib/IRGen/IRGenModule.cpp

@@ -428,6 +428,7 @@ namespace RuntimeConstants {
   const auto NoReturn = llvm::Attribute::NoReturn;
   const auto NoUnwind = llvm::Attribute::NoUnwind;
   const auto ZExt = llvm::Attribute::ZExt;
+  const auto FirstParamReturned = llvm::Attribute::Returned;
 } // namespace RuntimeConstants
 
 // We don't use enough attributes to justify generalizing the
@@ -436,6 +437,11 @@ namespace RuntimeConstants {
 static bool isReturnAttribute(llvm::Attribute::AttrKind Attr) {
   return Attr == llvm::Attribute::ZExt;
 }
+// Similar to the 'return' attribute we assume that the 'returned' attributed is
+// associated with the first function parameter.
+static bool isReturnedAttribute(llvm::Attribute::AttrKind Attr) {
+  return Attr == llvm::Attribute::Returned;
+}
 
 llvm::Constant *swift::getRuntimeFn(llvm::Module &Module,
                       llvm::Constant *&cache,
@@ -471,15 +477,19 @@ llvm::Constant *swift::getRuntimeFn(llvm::Module &Module,
 
     llvm::AttrBuilder buildFnAttr;
     llvm::AttrBuilder buildRetAttr;
+    llvm::AttrBuilder buildFirstParamAttr;
 
     for (auto Attr : attrs) {
       if (isReturnAttribute(Attr))
         buildRetAttr.addAttribute(Attr);
+      else if (isReturnedAttribute(Attr))
+        buildFirstParamAttr.addAttribute(Attr);
       else
         buildFnAttr.addAttribute(Attr);
     }
     fn->addAttributes(llvm::AttributeList::FunctionIndex, buildFnAttr);
     fn->addAttributes(llvm::AttributeList::ReturnIndex, buildRetAttr);
+    fn->addParamAttrs(0, buildFirstParamAttr);
   }
 
   return cache;

test/IRGen/weak.sil

@@ -1,4 +1,5 @@
 // RUN: %target-swift-frontend -assume-parsing-unqualified-ownership-sil -emit-ir %s | %FileCheck %s
+// RUN: %target-swift-frontend -assume-parsing-unqualified-ownership-sil -O -S %s | %FileCheck %s --check-prefix=TAILCALL
 
 // REQUIRES: CPU=x86_64
 // XFAIL: linux
@@ -15,15 +16,15 @@ sil_stage canonical
 
 import Swift
 
-class C {}
+public class C {}
 sil_vtable C {}
 sil @_T04weak1CCfD : $@convention(method) (C) -> ()
 
 protocol P : class {
   func explode()
 }
 
-struct A {
+public struct A {
   weak var x : C?
 }
 
@@ -113,13 +114,19 @@ bb0(%0 : $Optional<P>):
 // CHECK-NEXT: [[T0:%.*]] = bitcast [[A]]* [[DEST]] to [[OPAQUE]]*
 // CHECK-NEXT: ret [[OPAQUE]]* [[T0]]
 
+// TAILCALL: __T04weak1AVwCP:
+// TAILCALL:  jmp     _swift_weakCopyInit
+
 //   destroy
 // CHECK:    define linkonce_odr hidden void @_T04weak1AVwxx([[OPAQUE]]* noalias [[ARG:%.*]], [[TYPE]]*
 // CHECK:      [[T0:%.*]] = bitcast [[OPAQUE]]* [[ARG]] to [[A]]*
 // CHECK-NEXT: [[T1:%.*]] = getelementptr inbounds [[A]], [[A]]* [[T0]], i32 0, i32 0
 // CHECK-NEXT: call void @swift_weakDestroy([[WEAK]]* [[T1]])
 // CHECK-NEXT: ret void
 
+// TAILCALL: __T04weak1AVwxx:
+// TAILCALL:  jmp     _swift_weakDestroy
+
 //   initializeWithCopy
 // CHECK:    define linkonce_odr hidden [[OPAQUE]]* @_T04weak1AVwcp([[OPAQUE]]* noalias [[DEST_OPQ:%.*]], [[OPAQUE]]* noalias [[SRC_OPQ:%.*]], [[TYPE]]*
 // CHECK:      [[DEST:%.*]] = bitcast [[OPAQUE]]* [[DEST_OPQ]] to [[A]]*
@@ -130,6 +137,9 @@ bb0(%0 : $Optional<P>):
 // CHECK-NEXT: [[T0:%.*]] = bitcast [[A]]* [[DEST]] to [[OPAQUE]]*
 // CHECK-NEXT: ret [[OPAQUE]]* [[T0]]
 
+// TAILCALL: __T04weak1AVwcp:
+// TAILCALL:  jmp     _swift_weakCopyInit
+
 //   assignWithCopy
 // CHECK:    define linkonce_odr hidden [[OPAQUE]]* @_T04weak1AVwca([[OPAQUE]]* [[DEST_OPQ:%.*]], [[OPAQUE]]* [[SRC_OPQ:%.*]], [[TYPE]]*
 // CHECK:      [[DEST:%.*]] = bitcast [[OPAQUE]]* [[DEST_OPQ]] to [[A]]*
@@ -140,6 +150,9 @@ bb0(%0 : $Optional<P>):
 // CHECK-NEXT: [[T0:%.*]] = bitcast [[A]]* [[DEST]] to [[OPAQUE]]*
 // CHECK-NEXT: ret [[OPAQUE]]* [[T0]]
 
+// TAILCALL: __T04weak1AVwca:
+// TAILCALL:  jmp     _swift_weakCopyAssign
+
 //   assignWithTake
 // CHECK:    define linkonce_odr hidden [[OPAQUE]]* @_T04weak1AVwta([[OPAQUE]]* noalias [[DEST_OPQ:%.*]], [[OPAQUE]]* noalias [[SRC_OPQ:%.*]], [[TYPE]]*
 // CHECK:      [[DEST:%.*]] = bitcast [[OPAQUE]]* [[DEST_OPQ]] to [[A]]*
@@ -149,3 +162,12 @@ bb0(%0 : $Optional<P>):
 // CHECK-NEXT: call [[WEAK]]* @swift_weakTakeAssign([[WEAK]]* [[DEST_X]], [[WEAK]]* [[SRC_X]])
 // CHECK-NEXT: [[T0:%.*]] = bitcast [[A]]* [[DEST]] to [[OPAQUE]]*
 // CHECK-NEXT: ret [[OPAQUE]]* [[T0]]
+
+// TAILCALL: __T04weak1AVwtk:
+// TAILCALL:  jmp     _swift_weakTakeInit
+
+// TAILCALL: __T04weak1AVwta:
+// TAILCALL:  jmp     _swift_weakTakeAssign
+
+// TAILCALL: __T04weak1AVwTK:
+// TAILCALL:  jmp     _swift_weakTakeInit