+1 for removing constant folding for floats (besides conversion of -<literal>). There are just too many things to worry about: FPU rounding mode and precision, floating-point signals and flags, effect of compiler flags, and the potential benefit seems small.
If you're talking about the existing peepholer optimization that has been in-place for years, I think it would be better to leave it as-is. It's better to have the compiler do the work than to have a programmer thinking he/she needs to do it by hand (reducing readability by introducing magic numbers). The code for the lsum() recipe is more readable with a line like: exp = long(mant * 2.0 ** 53) than with exp = long(mant * 9007199254740992.0) It would be ashamed if code written like the former suddenly started doing the exponentation in the inner-loop or if the code got rewritten by hand as shown. The list of "things to worry about" seems like the normal list of issues associated with doing anything in floating point. Python is already FPU challenged in that it offers nearly zero control over the FPU or direct access to signals and flags. Every step of a floating point calculation in Python gets written-out to a PyFloat object and is squeezed back into a C double (potentially introducing double-rounding if extended precision had be used by the FPU). Disabling the peepholer doesn't change this situation. Raymond