Re: Safe transposition of logical and operands

[Martin Uecker <muecker@gwdg.de>]

Am Montag, dem 18.09.2023 um 19:56 +0200 schrieb Paul Floyd via Gcc:
> 
> On 18-09-23 16:55, Richard Biener wrote:
> 
> > What you could do is report the access only on the point of use of
> > the accessed value?  (and disregard when the register holding the
> > value is re-used)
> 
> Hi Richard
> 
> Not sure that I follow what you're saying.
> 
> memcheck triggers errors like this at conditional branching opcodes 
> where it determines that the condition is undefined.
> 
> There are mechanisms to de-duplicate errors, so once an error is emitted 
> it won't be printed again.
> 
> However, one of our goals is no false positives. This is one example 
> that is slipping through the cracks.
> 
I do not understand why memcheck cares about the potential trap when
deciding to do the backwards transformation that combines the two
comparisons?  Can't you just remove this condition?  I assume it
is meant as a filter to only transform cases which really come
from an '&&' condition in the source, but as this example show, this
is too strict. Or am I missing something?


Martin