From 62475afaf26d2372a58345a55a2748d532f2bea4 Mon Sep 17 00:00:00 2001
From: "Duncan P. N. Exon Smith" <dexonsmith@apple.com>
Date: Tue, 20 Jan 2015 00:58:46 +0000
Subject: [PATCH] IR: Canonicalize GenericDwarfNode empty headers to null

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@226532 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/IR/Metadata.cpp           | 4 ++++
 unittests/IR/MetadataTest.cpp | 8 ++++++++
 2 files changed, 12 insertions(+)

diff --git a/lib/IR/Metadata.cpp b/lib/IR/Metadata.cpp
index 97976308fcd..fc1f3e7a3cf 100644
--- a/lib/IR/Metadata.cpp
+++ b/lib/IR/Metadata.cpp
@@ -753,6 +753,10 @@ GenericDwarfNode *GenericDwarfNode::getImpl(LLVMContext &Context, unsigned Tag,
                                             ArrayRef<Metadata *> DwarfOps,
                                             StorageType Storage,
                                             bool ShouldCreate) {
+  // Canonicalize empty string to a nullptr.
+  if (Header && Header->getString().empty())
+    Header = nullptr;
+
   unsigned Hash = 0;
   if (Storage == Uniqued) {
     GenericDwarfNodeInfo::KeyTy Key(Tag, Header, DwarfOps);
diff --git a/unittests/IR/MetadataTest.cpp b/unittests/IR/MetadataTest.cpp
index f2140d62172..e2ed3d7946b 100644
--- a/unittests/IR/MetadataTest.cpp
+++ b/unittests/IR/MetadataTest.cpp
@@ -596,6 +596,14 @@ TEST_F(GenericDwarfNodeTest, get) {
   EXPECT_EQ(N, GenericDwarfNode::get(Context, 15, Header, Ops1));
 }
 
+TEST_F(GenericDwarfNodeTest, getEmptyHeader) {
+  // Canonicalize !"" to null.
+  auto *Header = MDString::get(Context, "");
+  EXPECT_NE(nullptr, Header);
+  auto *N = GenericDwarfNode::get(Context, 15, Header, None);
+  EXPECT_EQ(nullptr, N->getHeader());
+}
+
 typedef MetadataTest MetadataAsValueTest;
 
 TEST_F(MetadataAsValueTest, MDNode) {