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Re: [PATCH][4.3] Deprecate -ftrapv


On Sat, 1 Mar 2008, Joseph S. Myers wrote:

> On Fri, 29 Feb 2008, Mark Mitchell wrote:
> 
> > 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.
> 
> Obviously you need to keep the functions in libgcc in any event for the 
> sake of old object code (just as we keep __eprintf there), even if you 
> make GCC generate inline code rather than libcalls or remove the option 
> entirely.
> 
> You also need to deal with fold, which will optimize away potentially 
> trapping computations with -ftrapv and runs before gimplification 
> (possibly in association with making fold run at gimplification time and 
> not before).

It should not - at least we have various tests in place to ensure fold
does not remove traps nor insert traps.  Of course this is a very badly
tested part of the compiler, so possibly both may happen.

Richard.


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