Re: [RFC] Fold floating-point comparisons

[Paolo Bonzini <paolo dot bonzini at polimi dot it>]

> This lack of RTL documentation and conflicting beliefs in behaviour
> creates real problems.  For example, the C99 standard requires that
> isunordered, isgreater, isgreaterequal etc... explicitly don't trap.
> However, rtlanal.c's may_trap_p reveals that at the RTL level all of
> the corresponding RTL codes (UNORDERED, UNLE, UNLT etc..) are currently
> implemented assuming that they do trap.

Are they?  Remember that the mode of the comparison is *not* a floating 
point mode -- you have (unlt:BI x y), not (unlt:DF x y). More 
interesting is the fact that LTGT is not said to trap.

BTW, isgreater (x, y) is expanded (using c-common.c's 
expand_unordered_cmp) to NOT_EXPR (UNLE_EXPR (x, y)) exactly to avoid 
trapping.

Paolo