[PATCH] improve C++ code by changing fold-const.c

Mark Mitchell mark@codesourcery.com
Sat May 22 12:47:00 GMT 2004


Andrew Pinski wrote:

>
> On May 21, 2004, at 22:02, Mark Mitchell wrote:
>
>> Strongly agree.
>> There are places in the front ends, at least that assume that the 
>> tree structure is type correct, using explicit NOP_EXPRs to convert 
>> where necessary.  If the optimizers are confused by NOP_EXPRs, then 
>> they should be fixed -- that should generally be an easy fix.  (Note 
>> that a NOP_EXPR is a promise that the underlying bits do not change.)
>
>
> Maybe it is just me but the underlying types are the same as in the 
> second series
> of patches I just check for equality instead of compatibly (which I 
> thought would
> do the right thing any ways as the C++ front-end uses same_type_p 
> which calls comptypes
> which is what the langhook does).

More fundamentally, I want to see the C++ front end represent code in a 
manner that is as close as possible to the original source code -- 
except that things like overloading should be resolved, implicit 
conversions should be made explicit, etc.   Part of the reason for that 
is to that the C++ front end can be used for other things in other 
contexts.  If it weren't necessary to fold constants in order to perform 
certain semantic checks in C++, I wouldn't even bother with that!

The optimizers should be capable of resolving these kinds of things 
themselves.

> Oh by the way I notice that C++ front-end uses CONVERT_EXPR instead of 
> NOP_EXPR
> when converting between pointer and reference types anyways which is 
> wrong as
> CONVERT_EXPR is defined as creating code which this conversion does 
> not.  There
> are most likely more like this. 

Yes, that certainly sounds like a bug.

-- 
Mark Mitchell
CodeSourcery, LLC
(916) 791-8304
mark@codesourcery.com



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