On 09/29/2010 04:31 PM, Michael Eager wrote: > float a = 1.0, b = 2.0, x = NaN; > (a < b) generates the same condition flags as (a < x). ... > Are there other processors which do this? How do they > handle generating IEEE std compliant code?
It looks like there is a bunch of code under config that's conditionalized on flag_finite_math_only, which disables support for NaN and Inf. At a glance, rs6000_generate_compare may be relevant. > > A related problem is that CSE will optimize FP comparisons > and garble the result. (This doesn't happen with soft-fp.) > > int r = 0, s = 0; > float a = 1.0, x = NaN; > > r = (a <= x); > s = (a > x); > > should result in r == s == 0. CSE translates this (more > or less) into > > r = (a <= x); > s = !r; > > Is there a way to prevent CSE from optimizing FP comparisons? Add the missing check vs HONOR_NANS. This is clearly a bug. r~
