C++11 constexpr: Add note stacks containing backtraces if constant evaluation

fails within a call to a constexpr function. Add -fconstexpr-backtrace-limit
argument to driver and frontend, to control the maximum number of notes so
produced (default 10). Fix APValue printing to be able to pretty-print all
APValue types, and move the testing for this functionality from a unittest to
a -verify test now that it's visible in clang's output.

llvm-svn: 146749

1 files changed, 1 insertions, 0 deletions

diff --git a/clang/lib/Basic/Diagnostic.cpp b/clang/lib/Basic/Diagnostic.cpp
index 7ea296233a2..16435721590 100644
--- a/clang/lib/Basic/Diagnostic.cpp
+++ b/clang/lib/Basic/Diagnostic.cpp
@@ -53,6 +53,7 @@ DiagnosticsEngine::DiagnosticsEngine(
 
   ErrorLimit = 0;
   TemplateBacktraceLimit = 0;
+  ConstexprBacktraceLimit = 0;
 
   Reset();
 }