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Re: [Qemu-devel] [RFC] [tcg] Idea on refactoring target code generation

From: Paolo Bonzini
Subject: Re: [Qemu-devel] [RFC] [tcg] Idea on refactoring target code generation loop (gen_intermediate_code)
Date: Fri, 8 Apr 2016 16:14:24 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.6.0

On 08/04/2016 15:15, Markus Armbruster wrote:
> > On the other hand, minimal usage of templates instead of some of the
> > preprocessor gunk we have would be a very good thing IMNSHO.  I am
> > referring to the multiply included header files and to the macros with
> > type arguments (mostly QOM casts).
> >
> > I don't think we need more C++ than that, but using templates as
> > basically a type-safe preprocessor would improve QEMU a little bit.
> > More rarely, lambdas could replace some preprocessor magic too, but
> > that's C11 and not many compilers support them.
> >
> > But I won't weep if people say no because we have a lot other
> > low-hanging fruit to make QEMU better (especially the header file
> "No!"  (Hey, you asked for it)
> Back to serious.  As Peter Maydell said, "if we move away from C I'd
> rather it to be a language that's nicer than C rather than one that's
> uglier and larger and still retains all of C's flaws."

Sure, except that one plan is feasible now and can be done in small
steps; the other is not feasible now (for example Rust is not even
packaged in Fedora) and entails pretty much a rewrite of the whole code

> People sometimes propose to defang C++ by subsetting and/or coding
> conventions.  I'll take that seriously when I see the tool that
> rigorously checks adherence to subset / convention.

The problem with subsetting and conventions is that they always come
with exceptions, besides the fact that no one writes the tool.

So I prefer common sense :) and common sense says that a million-line
codebase that mixes procedural, home-grown OO and language OO is going
to stink from ten miles.  And maintainers sit at most two feet from the

Really even just -Wc++-compat would be a nice improvement so we enjoy a
little more type safety.  IMHO, C++'s biggest tax is that Coccinelle
does not like it.

> > cleanups that Markus started and I want to conclude very early in 2.7).
> Speaking of which: the plan was you post yours for 2.7, and then I can
> build on top (assuming there's useful work left), right?

I have rebased my stuff already, but I'm going to disappear in about a
week and for the first week or two after the 2.6 release (depending on
whether it slips or not).  Also, I will travel most of next week.  So I
either I'll post it soonish or it will have to wait a little.

Anyhow, there's definitely useful work left from your last two patches,
even more so after Veronia Bahaa cleaned up qemu-common.h substantially
so there may be more pointless inclusions of it and fewer headers that
really need it.


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