RE: [PATCH] Fix for PR c/57563

["Joseph S. Myers" <joseph@codesourcery.com>]

On Mon, 10 Jun 2013, Iyer, Balaji V wrote:

> > You don't say what the actual error was, and neither does the original PR.
> > But if it was an ICE from an EXCESS_PRECISION_EXPR getting to the gimplifier,
> > that suggests that c_fully_fold isn't getting called somewhere it should be - and
> > probably calling c_fully_fold is the correct fix rather than inserting a cast.  If you
> > can get such ICEs for EXCESS_PRECISION_EXPR, it's quite possible you might get
> > them for C_MAYBE_CONST_EXPR as well (e.g. try using 0 / 0, or compound
> > literals of variably modified type, in various places in the affected expressions),
> > which should be fixed by using c_fully_fold but not by inserting a cast.
> 
> It was not. It was actually a type mismatch between double and long 
> double caught in verify_gimple_in_seq function.  So, is it OK for trunk?

A cast still doesn't make sense conceptually.  Could you give a more 
detailed analysis of what the trees look like at this point where you are 
inserting this cast, and how you get to a mismatch?

EXCESS_PRECISION_EXPR can be thought of as a conversion operator.  It 
should only appear at the top level of an expression.  At the point where 
excess precision should be removed - the value converted to its semantic 
type - either the expression with excess precision should be folded using 
c_fully_fold (if this is the expression of an expression statement, or 
otherwise will go inside a tree that c_fully_fold does not recurse 
inside), or the operand of the EXCESS_PRECISION_EXPR should be converted 
to the semantic type with the "convert" function.  In neither case is 
generating a cast appropriate; that's for when the user actually wrote a 
cast in their source code.

-- 
Joseph S. Myers
joseph@codesourcery.com