[Support] Add a UniqueStringSaver: like StringSaver, but deduplicating.

Summary: Clarify contract of StringSaver (it null-terminates, callers rely on it).

Reviewers: hokein

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D49596

llvm-svn: 337677

1 files changed, 7 insertions, 0 deletions

diff --git a/llvm/lib/Support/StringSaver.cpp b/llvm/lib/Support/StringSaver.cpp
index 335fce3a7bb..1ded2bdb09d 100644
--- a/llvm/lib/Support/StringSaver.cpp
+++ b/llvm/lib/Support/StringSaver.cpp
@@ -17,3 +17,10 @@ StringRef StringSaver::save(StringRef S) {
   P[S.size()] = '\0';
   return StringRef(P, S.size());
 }
+
+StringRef UniqueStringSaver::save(StringRef S) {
+  auto R = Unique.insert(S);
+  if (R.second)                 // cache miss, need to actually save the string
+    *R.first = Strings.save(S); // safe replacement with equal value
+  return *R.first;
+}