Fix assertion when merging multiple empty AttributeLists

Patch by Nicholas Wilson!

Differential Revision: https://reviews.llvm.org/D33627

llvm-svn: 304300

2 files changed, 11 insertions, 0 deletions

diff --git a/llvm/lib/IR/Attributes.cpp b/llvm/lib/IR/Attributes.cpp
index 19b7c302723..a6d1c9035af 100644
--- a/llvm/lib/IR/Attributes.cpp
+++ b/llvm/lib/IR/Attributes.cpp
@@ -1006,6 +1006,10 @@ AttributeList AttributeList::get(LLVMContext &C,
   for (AttributeList List : Attrs)
     MaxSize = std::max(MaxSize, List.getNumAttrSets());
 
+  // If every list was empty, there is no point in merging the lists.
+  if (MaxSize == 0)
+    return AttributeList();
+
   SmallVector<AttributeSet, 8> NewAttrSets(MaxSize);
   for (unsigned I = 0; I < MaxSize; ++I) {
     AttrBuilder CurBuilder;
diff --git a/llvm/unittests/IR/AttributesTest.cpp b/llvm/unittests/IR/AttributesTest.cpp
index 7af4aebd540..ab018d84538 100644
--- a/llvm/unittests/IR/AttributesTest.cpp
+++ b/llvm/unittests/IR/AttributesTest.cpp
@@ -82,4 +82,11 @@ TEST(Attributes, AddMatchingAlignAttr) {
   EXPECT_TRUE(AL.hasParamAttribute(0, Attribute::NonNull));
 }
 
+TEST(Attributes, EmptyGet) {
+  LLVMContext C;
+  AttributeList EmptyLists[] = {AttributeList(), AttributeList()};
+  AttributeList AL = AttributeList::get(C, EmptyLists);
+  EXPECT_TRUE(AL.isEmpty());
+}
+
 } // end anonymous namespace