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

[Dmitry Zhurikhin]

On 05/20/2011 11:35 PM, Aurelien Jarno wrote:
> 
> On Fri, May 20, 2011 at 04:39:27PM +0400, 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.
> 
> How are the tests done? Are they done with linux-user, or running the
> executables in qemu-system-xxx?
They were run in user mode on a dedicated machine not doing anything
else.  We found system emulation to be too volatile for measuring
anything.  Anyway even with user mode and on a dedicated machine there
are some weird performance jumps we can't explain but overall SPEC seems
stable enough to notice influence of such changes in code generation.

> 
>> ...

        Dmitry