basic VRP min/max range overflow question

[Mike Stump]

General note, please, this list is for developers of gcc to develop  
gcc.  Using it as a way to teach yourself how to read the C standard,  
isn't ok, please stop.


On Saturday, June 18, 2005, at 07:15  AM, Paul Schlie wrote:
> Maybe I didn't phrase my statement well;

I think you did, you are just wrong.  Please quote the sentence that  
says the the program behaves in accordance with 5.1.2.3, if you can  
find none, then, trivially, there is no such requirement.  If you can  
find it, you can quote it.  Failure to find it, means either, you  
didn't look hard enough, or there is none.

Here, let me try again, in a slightly different way:

   --If a program contains no violations of the rules  in  this   
Interna-
     tional  Standard,  a  conforming  implementation  shall,  within  
its
     resource limits, accept and correctly execute2) that program.

   --If  a program contains a violation of a rule for which no  
diagnostic
     is required, this International Standard places  no   
requirement  on
     implementations with respect to that program.

   1.4.12  undefined behavior                            
[defns.undefined]
   behavior, such as might arise upon use of an  erroneous  program   
con-
   struct  or  of  erroneous  data,  for  which  the  Standard  
imposes no
   requirements.  Undefined behavior may also be expected when the   
stan-
   dard  omits  the  description  of any explicit definition of  
behavior.

Read it slowly, carefully, then instead of replying, go ask 100  
programmers not on this list what they think the words mean, listen  
to them.  Come back here and summarize, if the result is different  
from what we represent.

> I fully agree with the cited paragraph above which specifically  
> says a program containing unspecified behavior "shall be a   
> correct  program  and  act  in  accordance  with 5.1.2.3". Which  
> specifies program execution, in terms of an abstract machine model,  
> which correspondingly requires:

I love it, you quote 5.1.2.3, but that section has no relevance to  
the program, if you can't find something that gives it relevance.  Go  
back and try again.

> Therefore regardless of the result of an "undefined" result/ 
> operation at
> it's enclosing sequence point, the remaining program must continue  
> to abide
> by the specified semantics of the language.

Nope.  You have failed to grasp that `can do anything' actually means  
can do anything.  If the standard mean to say that all preceding  
semantics must be observable, the standard would say that, if you can  
find where it says that all observable semantics are required in all  
sequence points before the one containing the undefined behavior,  
then, maybe that standard doesn't say that.