Use IRGenFunction::coerceValue suggested by @aschwaighofer.

Author: rxwei

lib/IRGen/GenFunc.cpp

@@ -1244,20 +1244,8 @@ static llvm::Function *emitPartialApplicationForwarder(IRGenModule &IGM,
     // cast to the result type - it could be substituted.
     if (origConv.getSILResultType().hasTypeParameter()) {
       auto ResType = fwd->getReturnType();
-      if (auto *structType = dyn_cast<llvm::StructType>(ResType)) {
-        // Cast all struct elements to the desired type.
-        llvm::Value *castResult = llvm::UndefValue::get(structType);
-        for (auto i : range(structType->getStructNumElements())) {
-          auto desiredEltTy = structType->getElementType(i);
-          auto elt = subIGF.Builder.CreateExtractValue(callResult, {i});
-          auto castElt = subIGF.Builder.CreateBitCast(elt, desiredEltTy);
-          castResult =
-              subIGF.Builder.CreateInsertValue(castResult, castElt, {i});
-        }
-        callResult = castResult;
-      }
-      else
-        callResult = subIGF.Builder.CreateBitCast(callResult, ResType);
+      if (ResType != callResult->getType())
+        callResult = subIGF.coerceValue(callResult, ResType, subIGF.IGM.DataLayout);
     }
     subIGF.Builder.CreateRet(callResult);
   }