Merge pull request #293 from manavgabhawala/master

Fixes [SR-78] swift compiler seg fault

Author: jckarter

lib/IRGen/GenType.cpp

@@ -2031,8 +2031,9 @@ SILType irgen::getSingletonAggregateFieldType(IRGenModule &IGM,
 
     // If there's only one stored property, we have the layout of its field.
     auto allFields = structDecl->getStoredProperties();
+    
     auto field = allFields.begin();
-    if (std::next(field) == allFields.end())
+    if (!allFields.empty() && std::next(field) == allFields.end())
       return t.getFieldType(*field, *IGM.SILMod);
 
     return SILType();

test/IRGen/generic_structs.swift

@@ -0,0 +1,26 @@
+// RUN: %target-swift-frontend -primary-file %s -emit-ir | FileCheck %s
+
+struct A<T1, T2>
+{
+  var b: T1
+  var c: T2
+  var d: B<T1, T2>
+}
+struct B<T1, T2>
+{
+  var c: T1
+  var d: T2
+}
+
+struct C<T1>
+{}
+struct D<T2>
+{}
+
+struct Foo<A1, A2>
+{
+  var b: Bar<A1, A2>
+}
+
+struct Bar {
+}