StringRef: Extend constexpr capabilities and introduce ConstStringRef

(1) Add llvm_expect(), an asserting macro that can be evaluated as a constexpr
    expression as well as a runtime assert or compiler hint in release builds. This
    technique can be used to construct functions that are both unevaluated and
    compiled depending on usage.

(2) Update StringRef using llvm_expect() to preserve runtime assertions while
    extending the same checks to static asserts in C++11 builds that support the
    feature.

(3) Introduce ConstStringRef, a strong subclass of StringRef that references
    compile-time constant strings. It's convertible to, but not from, ordinary
    StringRef and thus can be used to add compile-time safety to various interfaces
    in LLVM and clang that only accept fixed inputs such as diagnostic format
    strings that tend to get misused.

llvm-svn: 200187

1 files changed, 1 insertions, 1 deletions

diff --git a/llvm/lib/Support/ErrorHandling.cpp b/llvm/lib/Support/ErrorHandling.cpp
index 1aa8303b9e2..141319ca4ea 100644
--- a/llvm/lib/Support/ErrorHandling.cpp
+++ b/llvm/lib/Support/ErrorHandling.cpp
@@ -58,7 +58,7 @@ void llvm::report_fatal_error(const std::string &Reason, bool GenCrashDiag) {
   report_fatal_error(Twine(Reason), GenCrashDiag);
 }
 
-void llvm::report_fatal_error(StringRef Reason, bool GenCrashDiag) {
+void llvm::report_fatal_error(const StringRef &Reason, bool GenCrashDiag) {
   report_fatal_error(Twine(Reason), GenCrashDiag);
 }