From 54829bb3ff750cf8061fcd82db46f3596fa9cbac Mon Sep 17 00:00:00 2001
From: Haojian Wu <hokein@google.com>
Date: Mon, 20 Aug 2018 13:12:54 +0000
Subject: [PATCH] Fix an undefined behavior when storing an empty StringRef.

Summary: Passing a nullptr to memcpy is UB.

Reviewers: ioeric

Subscribers: llvm-commits, cfe-commits

Differential Revision: https://reviews.llvm.org/D50966

llvm-svn: 340170
---
 llvm/lib/Support/StringSaver.cpp | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/llvm/lib/Support/StringSaver.cpp b/llvm/lib/Support/StringSaver.cpp
index 1ded2bdb09de..bf0ac8de9821 100644
--- a/llvm/lib/Support/StringSaver.cpp
+++ b/llvm/lib/Support/StringSaver.cpp
@@ -13,7 +13,8 @@ using namespace llvm;
 
 StringRef StringSaver::save(StringRef S) {
   char *P = Alloc.Allocate<char>(S.size() + 1);
-  memcpy(P, S.data(), S.size());
+  if (!S.empty())
+    memcpy(P, S.data(), S.size());
   P[S.size()] = '\0';
   return StringRef(P, S.size());
 }