Re: [PATCH][4.3] Deprecate -ftrapv

[Robert Dewar <dewar at adacore dot com>]

Richard Guenther wrote:
> On Sat, 1 Mar 2008, Richard Kenner wrote:
>
> > > int f(int a, int b) { return 0 * (a + b); }
> > >
> > > get the potentially trapping arithmetic folded away.  If -ftrapv is to 
> > > have properly defined semantics, those must include trapping if (a + b) 
> > > overflows in the above code.
> > Why?  Is there any language that requires such semantics?
>
> Not exactly.  -ftrapv semantics are defined _very_ sparsely.
>
> "This option generates traps for signed overflow on addition,
> subtraction and multiplication operations."
>
> it doesn't say if it preserves traps on dead code, so Josephs
> interpretation is one possible valid one.

And anyway, no point in doing energetic exergesis on vague language
defining an option that has never worked anyway :-)

Part of "fixing" -ftrapv should be to carefully document exactly
what it does/is-intended-to-do (hopefully those are the same :-))
> Richard.