Question on performance

[Arnold Neumaier <Arnold.Neumaier@xxxxxxxxxxxx>]

I have a question about performance on current 754-conforming hardware:


Suppose I write code consisting only of 754 floating-point operations
and calls to simple customized additional functions such as
    nan2zero(x), which returns 0 if isnan(x), and x otherwise.


Will the code generated by a standard, good compiler run --

(i) essentially as efficient as without these function calls?

(ii) essentially as efficient as if it contained explicit case
distinctions?

(iii) intermediate but still efficient?

(iv) intermediate but still inefficient?


In case of (ii) or (iv), could a special purpose compiler do 
significantly better?



Arnold Neumaier