RE: bug report

["Jerome Vuarand" <jerome.vuarand@...>]

Roberto Ierusalimschy write:
> > Thierry Grellier reported a bug in Lua 5.1.1.  The bug only 
> happens in 
> > functions with more than 255 names/constants.  Then, the 
> interaction 
> > between contants and table accesses (e.g., "2*a.x") may 
> produce weird 
> > results. Bellow is an example (all results should be 2).
> > [...]
> 
> We could write a quick patch for this bug. However, we are 
> considering a more drastic measure: maybe it would be simpler 
> to remove constant folding optimization from Lua 5.1.
> 
> Currently, I am not sure constant folding is worth the 
> trouble. We had all kinds of problems with it: division and 
> module by zero, NaN results, problems with exotic lua_Number 
> types (which may need a state to create new values), etc. And 
> it adds very little to the language: it is very easy for the 
> programmer to define suitable local "constants" to avoid 
> recomputing constant expressions, when needed.

Consider the following hypothesis: "I'm not sure exactly when constant
folding happens, and if removing it would have a big impact on my
project". Could you present briefly general cases/conditions when
constant folding is extensively used by the compiler, when it works
gracefully, when compiler can't use it, and a simple patch that
desactivate it for worried people to test and benchmark in real world
situation ? That would give you valuable feedback on whether or not
applying your 'drastic' measure would have a negative impact.