avoid unnecessary register saves for setjmp

[Chris Lattner]

On Thu, 27 Nov 2003, Zack Weinberg wrote:
> Chris Lattner <sabre@nondot.org> writes:
> > On Thu, 27 Nov 2003, Zack Weinberg wrote:
> > Also, ideally, longjmp should run cleanups in intervening stackframes,
> > which the LLVM implementation does, just like for pthreads cancellation.
>
> Right.  (The IA64 psABI seems to anticipate that some people expect it
> *not* to, by providing longjmp_unwind.)

Really?  That seems to be directly against the C++ notion of construction
and destruction: that non-heap objects are guaranteed to be destroyed in
LIFO order.  I guess that people are used to not having longjmp work
"correctly"? :)

-Chris

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