From 9eee1df2a8be40b8642931c0c73f711a092e727f Mon Sep 17 00:00:00 2001
From: Manav Gabhawala <manav1907@gmail.com>
Date: Mon, 7 Dec 2015 01:08:45 -0500
Subject: [PATCH 1/4] Fixes [SR-78] swift compiler seg fault

Fixes a segmentation fault where the IRGen module would crash when a
generic (empty) struct was part of the source code because it tried to
call std::next on an end iterator.
---
 lib/IRGen/GenType.cpp            |  5 +++++
 test/IRGen/generic_structs.swift | 26 ++++++++++++++++++++++++++
 2 files changed, 31 insertions(+)
 create mode 100644 test/IRGen/generic_structs.swift

diff --git a/lib/IRGen/GenType.cpp b/lib/IRGen/GenType.cpp
index 3067a18fcf9f0..2e812ecf74e22 100644
--- a/lib/IRGen/GenType.cpp
+++ b/lib/IRGen/GenType.cpp
@@ -2032,6 +2032,11 @@ 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 there are no other fields exit early to prevent calling std::next on
+    // an invalid iterator.
+    if (field == allFields.end())
+      return SILType();
+    
     if (std::next(field) == allFields.end())
       return t.getFieldType(*field, *IGM.SILMod);
 
diff --git a/test/IRGen/generic_structs.swift b/test/IRGen/generic_structs.swift
new file mode 100644
index 0000000000000..97b4ededf2c40
--- /dev/null
+++ b/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 {
+}
\ No newline at end of file

From 06839c43ea7d1aaa700cb55c017b4b56100d2c91 Mon Sep 17 00:00:00 2001
From: Manav Gabhawala <manav1907@gmail.com>
Date: Mon, 7 Dec 2015 01:12:01 -0500
Subject: [PATCH 2/4] Check using .empty() instead of .end()

Updates to check for empty instead of checking iterator at end() for
more readability.
---
 lib/IRGen/GenType.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/IRGen/GenType.cpp b/lib/IRGen/GenType.cpp
index 2e812ecf74e22..e8842dfe0b056 100644
--- a/lib/IRGen/GenType.cpp
+++ b/lib/IRGen/GenType.cpp
@@ -2034,7 +2034,7 @@ SILType irgen::getSingletonAggregateFieldType(IRGenModule &IGM,
     auto field = allFields.begin();
     // If there are no other fields exit early to prevent calling std::next on
     // an invalid iterator.
-    if (field == allFields.end())
+    if (allFields.empty())
       return SILType();
     
     if (std::next(field) == allFields.end())

From e755c3f617673b64ffec048bbe09e51e37bf6ac1 Mon Sep 17 00:00:00 2001
From: Manav Gabhawala <manav1907@gmail.com>
Date: Mon, 7 Dec 2015 02:29:41 -0500
Subject: [PATCH 3/4] Refactored Into 2 Code Paths

Refactored the code so that there is only a single branch for when there is one stored property and the rest return a SILType() as per @simonmpilkington suggestion.
---
 lib/IRGen/GenType.cpp | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/lib/IRGen/GenType.cpp b/lib/IRGen/GenType.cpp
index e8842dfe0b056..fb6e2344cfaeb 100644
--- a/lib/IRGen/GenType.cpp
+++ b/lib/IRGen/GenType.cpp
@@ -2031,13 +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 there are no other fields exit early to prevent calling std::next on
-    // an invalid iterator.
-    if (allFields.empty())
-      return SILType();
     
-    if (std::next(field) == allFields.end())
+    auto field = allFields.begin();
+    if (!allFields.empty() && std::next(field) == allFields.end())
       return t.getFieldType(*field, *IGM.SILMod);
 
     return SILType();

From 8017cd2164ae5ca71894869f29ac214463169605 Mon Sep 17 00:00:00 2001
From: Manav Gabhawala <manav1907@gmail.com>
Date: Mon, 7 Dec 2015 13:52:52 -0500
Subject: [PATCH 4/4] Added empty newline at the end of test case

---
 test/IRGen/generic_structs.swift | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/test/IRGen/generic_structs.swift b/test/IRGen/generic_structs.swift
index 97b4ededf2c40..faaec4b3f4255 100644
--- a/test/IRGen/generic_structs.swift
+++ b/test/IRGen/generic_structs.swift
@@ -23,4 +23,4 @@ struct Foo<A1, A2>
 }
 
 struct Bar {
-}
\ No newline at end of file
+}