X-Git-Url: http://demsky.eecs.uci.edu/git/?a=blobdiff_plain;f=include%2Fllvm%2FSupport%2FErrorHandling.h;h=95b01095c1b25c89ae98ad52a22cf60b6043e15f;hb=525398e1376b0d61fe80a83ed2261e2e6e6ab4a3;hp=5eca438d8b4ac034ff0c3fab629f3f5d47b292b7;hpb=afd693cff38ea76188f8f895c75fdf24c90c606a;p=oota-llvm.git

diff --git a/include/llvm/Support/ErrorHandling.h b/include/llvm/Support/ErrorHandling.h
index 5eca438d8b4..95b01095c1b 100644
--- a/include/llvm/Support/ErrorHandling.h
+++ b/include/llvm/Support/ErrorHandling.h
@@ -86,16 +86,19 @@ namespace llvm {
                                                          unsigned line=0);
 }
 
-/// Prints the message and location info to stderr in !NDEBUG builds.
-/// This is intended to be used for "impossible" situations that imply
-/// a bug in the compiler.
+/// Marks that the current location is not supposed to be reachable.
+/// In !NDEBUG builds, prints the message and location info to stderr.
+/// In NDEBUG builds, becomes an optimizer hint that the current location
+/// is not supposed to be reachable.  On compilers that don't support
+/// such hints, prints a reduced message instead.
 ///
-/// In NDEBUG mode it only prints "UNREACHABLE executed".
-/// Use this instead of assert(0), so that the compiler knows this path
-/// is not reachable even for NDEBUG builds.
+/// Use this instead of assert(0).  It conveys intent more clearly and
+/// allows compilers to omit some unnecessary code.
 #ifndef NDEBUG
 #define llvm_unreachable(msg) \
   ::llvm::llvm_unreachable_internal(msg, __FILE__, __LINE__)
+#elif defined(LLVM_BUILTIN_UNREACHABLE)
+#define llvm_unreachable(msg) LLVM_BUILTIN_UNREACHABLE
 #else
 #define llvm_unreachable(msg) ::llvm::llvm_unreachable_internal()
 #endif