[cfe-dev] library builtins and exceptions

[Hal Finkel]

Ben, Chad, et al.,

Looking at the list of libm library builtins in Builtins.def, only cimag and creal are marked with 'n' (nothrow). Is this because the other functions can issue floating-point exceptions? It seems that this prevents the functions from being marked as 'nounwind' in the IR (but only in C++ mode). A couple of questions:

 1. Is this really necessary? First, if it is necessary, then it seems wrong for C (because we only don't emit nounwind for C++ codes). Also, if the function is already marked as 'readonly', is that not sufficient? A 'readonly' function can still trap (by dereferencing a null pointer, for example).

 2. If I'm right about the 'n' -> floating-point exception relationship, then it should be turned off when -fno-trapping-math is provided (but its not). If the answer to question 1 is, 'yes, it is needed", then is the best way to implement this to do the same thing here as is done for the 'e' (const when -fmath-errno=0) flag?

Thanks in advance,
Hal

-- 
Hal Finkel
Assistant Computational Scientist
Leadership Computing Facility
Argonne National Laboratory