[ObjC] Use empty Objective-C collection literal constants when

available.

Original patch by Douglas Gregor with minor modifications.

rdar://problem/20689633

llvm-svn: 300389

1 files changed, 14 insertions, 2 deletions

diff --git a/clang/lib/CodeGen/CGObjC.cpp b/clang/lib/CodeGen/CGObjC.cpp
index c011ab4dfc9..067718e2b8e 100644
--- a/clang/lib/CodeGen/CGObjC.cpp
+++ b/clang/lib/CodeGen/CGObjC.cpp
@@ -117,10 +117,22 @@ llvm::Value *CodeGenFunction::EmitObjCCollectionLiteral(const Expr *E,
   const ObjCArrayLiteral *ALE = dyn_cast<ObjCArrayLiteral>(E);
   if (!ALE)
     DLE = cast<ObjCDictionaryLiteral>(E);
-  
-  // Compute the type of the array we're initializing.
+
+  // Optimize empty collections by referencing constants, when available.
   uint64_t NumElements = 
     ALE ? ALE->getNumElements() : DLE->getNumElements();
+  if (NumElements == 0 && CGM.getLangOpts().ObjCRuntime.hasEmptyCollections()) {
+    StringRef ConstantName = ALE ? "__NSArray0__" : "__NSDictionary0__";
+    QualType IdTy(CGM.getContext().getObjCIdType());
+    llvm::Constant *Constant =
+        CGM.CreateRuntimeVariable(ConvertType(IdTy), ConstantName);
+    LValue LV = LValue::MakeAddr(Constant, IdTy,
+                                 Context.getTypeAlignInChars(IdTy), Context);
+    return Builder.CreateBitCast(EmitLoadOfScalar(LV, E->getLocStart()),
+                                 ConvertType(E->getType()));
+  }
+
+  // Compute the type of the array we're initializing.
   llvm::APInt APNumElements(Context.getTypeSize(Context.getSizeType()),
                             NumElements);
   QualType ElementType = Context.getObjCIdType().withConst();