Re: [Qemu-devel] [PATCH 0/6] Implement constant folding and copy propagation in TCG

[Andreas Färber]

Am 20.05.2011 um 21:37 schrieb Aurelien Jarno:

> On Fri, May 20, 2011 at 10:50:49AM -0700, Richard Henderson wrote:
> > On 05/20/2011 05:39 AM, Kirill Batuzov wrote:
> > > This series implements some basic machine-independent  
> > > optimizations.  They
> > > simplify code and allow liveness analysis do it's work better.
> > >
> > > Suppose we have following ARM code:
> > >
> > > movw    r12, #0xb6db
> > > movt    r12, #0xdb6d
> > >
> > > In TCG before optimizations we'll have:
> > >
> > > movi_i32 tmp8,$0xb6db
> > > mov_i32 r12,tmp8
> > > mov_i32 tmp8,r12
> > > ext16u_i32 tmp8,tmp8
> > > movi_i32 tmp9,$0xdb6d0000
> > > or_i32 tmp8,tmp8,tmp9
> > > mov_i32 r12,tmp8
> > >
> > > And after optimizations we'll have this:
> > >
> > > movi_i32 r12,$0xdb6db6db
> > >
> > > Here are performance evaluation results on SPEC CPU2000 integer  
> > > tests in
> > > user-mode emulation on x86_64 host.  There were 5 runs of each  
> > > test on
> > > reference data set.  The tables below show runtime in seconds for  
> > > all these
> > > runs.
> >
> > I totally agree that this sort of optimization is needed in TCG.
>
> I basically stopped working on constant propagation, as while the TCG
> code looked nicer, the resulting code was always slower.

Has anyone evaluated reusing LLVM optimization passes for TCG? Or  
maybe GIMPL if there's an equivalent?

Andreas