StringRef::copy shouldn't allocate anything for length 0 strings.

The BumpPtrAllocator currently doesn't handle zero length allocations well.
The discussion for how to fix that is ongoing.  However, there's no need
for StringRef::copy to actually allocate anything here anyway, so just
return StringRef() when we get a zero length copy.

Reviewed by David Blaikie

llvm-svn: 264201

1 files changed, 9 insertions, 0 deletions

diff --git a/llvm/unittests/ADT/StringRefTest.cpp b/llvm/unittests/ADT/StringRefTest.cpp
index 6354026d7ae..66e5944b56e 100644
--- a/llvm/unittests/ADT/StringRefTest.cpp
+++ b/llvm/unittests/ADT/StringRefTest.cpp
@@ -589,6 +589,15 @@ TEST(StringRefTest, joinStrings) {
 
 TEST(StringRefTest, AllocatorCopy) {
   BumpPtrAllocator Alloc;
+  // First test empty strings.  We don't want these to allocate anything on the
+  // allocator.
+  StringRef StrEmpty = "";
+  StringRef StrEmptyc = StrEmpty.copy(Alloc);
+  EXPECT_TRUE(StrEmpty.equals(StrEmptyc));
+  EXPECT_EQ(StrEmptyc.data(), nullptr);
+  EXPECT_EQ(StrEmptyc.size(), 0u);
+  EXPECT_EQ(Alloc.getTotalMemory(), 0u);
+
   StringRef Str1 = "hello";
   StringRef Str2 = "bye";
   StringRef Str1c = Str1.copy(Alloc);