Add LLVM_ATTRIBUTE_NORETURN to report_bad_alloc_error

[aaronpuchert]

Summary

The attribute just means that there will be no regular return, it still
leaves room for exceptions to be thrown. It is easily verified: there
are no direct returns and the last statement is either a throw or a call
to abort.

Having the annotation helps static analyzers with this code from
Support/MemAlloc.h (slightly simplified):

LLVM_ATTRIBUTE_RETURNS_NONNULL inline void *safe_malloc(size_t Sz) {

void *Result = std::malloc(Sz);
if (Result == nullptr)
  report_bad_alloc_error("Allocation failed");
return Result;

}

Were report_bad_alloc_error to return regularly, the function would
return nullptr, contradicting the attribute.

[dblaikie]

Sounds good to me!

[aaron.ballman]

LGTM!

llvm/include/llvm/Support/ErrorHandling.h

 
 /// Restores default bad alloc error handling behavior.
 void remove_bad_alloc_error_handler();
 
 void install_out_of_memory_new_handler();
 
 /// Reports a bad alloc error, calling any user defined bad alloc
 /// error handler. In contrast to the generic 'report_fatal_error'
-/// functions, this function is expected to return, e.g. the user
-/// defined error handler throws an exception.
+/// functions, this function might not terminate, e.g. the user
+/// defined error handler throws an exception, but it won't return.
 ///
 /// Note: When throwing an exception in the bad alloc handler, make sure that
 /// the following unwind succeeds, e.g. do not trigger additional allocations
 /// in the unwind chain.
 ///
 /// If no error handler is installed (default), then a bad_alloc exception
 /// is thrown, if LLVM is compiled with exception support, otherwise an
 /// assertion is called.
-void report_bad_alloc_error(const char *Reason, bool GenCrashDiag = true);
+LLVM_ATTRIBUTE_NORETURN void report_bad_alloc_error(const char *Reason,
+                                                    bool GenCrashDiag = true);
 
 /// This function calls abort(), and prints the optional message to stderr.
 /// Use the llvm_unreachable macro (that adds location info), instead of
 /// calling this function directly.
 LLVM_ATTRIBUTE_NORETURN void
 llvm_unreachable_internal(const char *msg = nullptr, const char *file = nullptr,
                           unsigned line = 0);
 }