[Bug tree-optimization/21610] [4.0/4.1 Regression] ICE in make_decl_rtl

[Andrew Pinski]

On May 16, 2005, at 4:28 PM, joseph at codesourcery dot com wrote:
>> ------- Additional Comments From pinskia at gcc dot gnu dot org  
>> 2005-05-16 20:03 -------
>> (In reply to comment #3)
>>> If you get rid of decl_constant_value_for_broken_optimization then I
>>> suspect you'll lose some optimizations because fold doesn't operate 
>>> on SSA
>>> so some constant values won't be available to fold, only to later
>>> optimizations.  But you'll get rid of the only references to 
>>> "optimize" in
>>> the C front end other than those defining built-in macros, and the
>>> front-end shouldn't care about "optimize" in principle, and you'll
>>> probably get rid of some XFAILs in c9?-const-expr-?.c in the process.
>>
>> Why do you believe fold does not operate on SSA?
>
> Fold has optimizations working on large complicated trees of 
> expressions,
> looking at their subexpressions and subsubexpressions; such trees are 
> only
> available during parsing, before conversion to GIMPLE form.  If the
> constants aren't available in these non-GIMPLE trees then you lose the
> optimizations.  The folding called from the SSA optimizers can only 
> fold
> smaller fragments of trees.  Everything fold does which looks at
> subexpressions and subsubexpressions of non-GIMPLE trees can in 
> principle
> be done on GIMPLE but I don't think there's evidence that every such 
> fold
> optimization is implemented for GIMPLE.

Yes that is what the tree combiner would do but since I have not have 
time
to work it, we are missing more and more optimizations because not 
having
it.

-- Pinski