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From: Brian Drummond <brian@shapes.demon.co.uk>
Newsgroups: comp.lang.ada
Subject: Re: What's the eaerliest GNAT that can be built with 4.9.3?
Date: Tue, 23 Aug 2016 11:33:07 -0000 (UTC)
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On Mon, 22 Aug 2016 09:25:43 -0700, Lucretia wrote:

> As the subject really.
> 
> I've successfully built 4.9.3 with that bootstrap and then using the
> built 4.9.3 to build 5.1.0, so that's good, just need to know the other
> way around.

Not a definitive answer but I would expect 4.8.x to build cleanly enough.

At the other extreme, I can report complete build failures of 4.3 (for 
AVR-Ada) with compilers of the 4.5 era onwards, because they stopped 
accepting negative enums (!!!) in the C sources which were present in the 
earlier compilers. 

So I would place 4.4 as a lower bound of what *might* build and 4.8 as a 
likely upper bound.

Between those, you probably have to bisect...

-- Brian