Re: [tree-ssa] Problem with constant folding

[Zdenek Dvorak <rakdver at atrey dot karlin dot mff dot cuni dot cz>]

Hello,

>  >[snip] (http://gcc.gnu.org/ml/gcc-patches/2003-12/msg00786.html)
>  >
>  >> The patch below fixes the problem by preventing the overflowed constants
>  >> from being propagated.  It is probably way too conservative, but I was
>  >> not able to determine the place where to fix the problem in other way.
>  >
>  >... and unfortunately it is also wrong, since it fails to bootstrap. Does
>  >someone has an idea what is the right way to fix this?
> Your approach seems pretty reasonable.  And it seems extremely odd that
> it wouldn't bootstrap since it ought to just force such constants into
> new variables and prevent them from being propagated by the optimizers.
> 
> I'd suggest investigating why the patch didn't bootstrap.

because gimplification fails when constants are not considered to be
invariant.  I.e. I would need to check this directly in the optimizers.

But what bothers me is that I am not at all sure whether it indeed fixes
the real problem; we obviously handle overflowed constants wrongly
somewhere, and I have no idea where it is.

Zdenek