Re: [PATCH][4.3] Deprecate -ftrapv

[Mark Mitchell <mark at codesourcery dot com>]

Richard Guenther wrote:

> The tree optimizers do not recognize +-* of singed integers as
> possibly trapping which causes functions to become const/pure that
> should not and causes 'dead' code to be removed that should not.

Thanks for the explanations.  It seems like tree-ssa should in theory 
make it easier to implement this; for example, at the point of 
gimplification one could insert checks, and then just let everything 
else do its thing.  I don't see how libcalls and such would matter in 
that scheme.  I'm not denying that this is a project, though.

I fully agree that claiming things work when they don't is bad -- we 
don't want to lie to the users!  But, is the failure mode that we issue 
run-time errors when we shouldn't, or that we don't issue run-time 
errors when we should?  The latter is much less severe than the former.

I guess you've withdrawn the deprecation request, so maybe this is 
something of a moot point now?  I certainly agree that we shouldn't let 
a non-working feature stand in the way of improvements in 4.4.

Thanks,

--
Mark Mitchell
CodeSourcery
mark@codesourcery.com
(650) 331-3385 x713