Re: [Qemu-devel] WE NEED GCC 4 please

[Julian Seward <jseward@acm.org>]

> > > As it is, Fabrice's code generator will most likely be something
> > > similar to Paul's qops, which means that you have to invent a
> > > "primitive C" in which to write the miniops, and you will have to
> > > write a backend for _each_ and _every_ host CPU you support.

It's not a terribly big deal.  Writing backends is a lot easier than
writing front ends, since the back end can just emit some small convenient
subset of target instructions, whereas the front ends have to deal
with every stupid, obscure, weird-ass instruction that ever shows up.

QEMU is not the first project to post-process gcc's output.  The
Glasgow Haskell Compiler
(http://en.wikipedia.org/wiki/Glasgow_Haskell_Compiler)
did that for many years and it was always an immense amount of
hassle tracking the changes to gcc's code generation.  Having a
completely-independent-of-everything, standalone code generator is
definitely a lot easier in the end.

> Given the unwillingness of Fabrice to rely on some external project,
> though, I gave up even before I had something even rudimentary.

Perhaps Fabrice could commit this code generator on a branch, even if
it is not perfect yet.  That would at least provide something "real"
to assess; so far all we have is rumour and speculation.

J