handling setjmp/longjmp in new front-end

[Fergus Henderson <fjh at cs dot mu dot oz dot au>]

I'm working on a new GCC front-end, for Mercury
(<http://www.cs.mu.oz.au/mercury/>).  The existing Mercury compiler
generates C code that uses setjmp() and longjmp().  I'm not sure how
to handle this in the GCC front-end, because setjmp() may be a macro,
rather than a function, and because the definition of the jmpbuf type
may vary from platform to platform.

One possibility is to use __builtin_setjmp() and __builtin_longjmp()
instead.  This would also solve the problem with jmpbuf.

However, the documentation of __builtin_setjmp() says

 |    NOTE: This is intended for use by GNAT and the exception handling
 |    scheme in the compiler and will only work in the method used by
 |    them.

What exactly are the restrictions?  Is it just that __builtin_longjmp()
must always be called with the second argument being `1', or is there
more to it?

Are __builtin_setjmp() and __builtin_longjmp() supported on all targets?

-- 
Fergus Henderson <fjh@cs.mu.oz.au>  |  "I have always known that the pursuit
                                    |  of excellence is a lethal habit"
WWW: <http://www.cs.mu.oz.au/~fjh>  |     -- the last words of T. S. Garp.