RTC Thumb2 JIT enhancements

[Xerxes Rånby]

On 2010-03-17 15:01, Xerxes Rånby wrote:
> Hi!
>
> On 2010-03-11 12:23, ed at camswl.com wrote:
>   
>> Hi folks,
>>
>> The following are some enhancements I have made to the T2JIT over the past
>> month.
>>
>> I have tested the changes with various benchmarks, with Think Free Office,
>> and with the hotspot and lang portions of JTreg which all pass. The jdk
>> portion is still running.
>>
>> Unfortunately the diffs are quite large so I am submitting the diffs to
>> the list as 4 separate sets of diffs.
>>
>> Has the b18 release been split off yet? I would prefer these changes not
>> to go into the b18 release as they have not had sufficient testing yet.
>>
>>   
>>     
> A bit strange to have them left in limbo.. surely they are designed and
> tested to work with the openjdk used in 1.7.x but they are also too new
> to be included in that release branch since icedtea6 1.7.x only accepts
> bugfixes and no new features....
> The new icedtea6 1.8 release using openjdk b18 that will branch any time
> now from icedtea6 trunk do already contain the first implementation of
> the t2jit and does also full bootstrap compile and runs with these four
> new patches applied when I tested it.
>
> If we do not include these new t2 fixes for the 1.8 branch then we have
> to play catchup with the upcoming openjdk b19 and potentially with a new
> hotspot hs17.
>
> Both icedtea6 1.7.x and icedtea6 1.8 uses the same hotspot, hs16, so
> they should both be ok I think.
>   
Correction: both uses the same hotspot *hs14-b16*     with an option to
build with hs16-b13 (--with-hotspot-build=hs16)
sorry for this confusion.

cheers
Xerxes
> With all this said I think the patches looks great, they apply build and
> run using icedtea6 trunk, and I am in favour for them to go in so that
> they can be included in the next 1.8 release.
>
> Cheers
> Xerxes
>
>   
>> Regards,
>> Ed.
>>
>> - Support for frameless compilation
>>
>> 	Local variables and interpreter state are now addressed from Java SP
>> 	rather than separate 'istate' (R8) register. R8 now free for register
>> 	allocation giving 6 allocatable registers instead of 5.
>>
>> - Support for compilation of methods containing monitorenter / monitorexit
>>
>> 	monitorenter / monitorexit moved from asm to C so they can be called
>> 	by JIT code compilation of monitorenter / monitorexit containinng
>> 	methods uses frame adressing because stack can expand dynamically to
>> 	accomodate monitors.
>>
>> - Interpreter caches 'thread' in a register
>>
>> 	Interpreter reworked to cache 'thread' in a register. Involved
>> 	removal of one 'tmp' register in interpreter to make room for
>> 	'thread' register. Interpreter and JIT are now consistent in register
>> 	usage.
>>
>> - Compression of JIT 'header'
>>
>> 	Removed the OSR entry from the JIT header. Previously, each JITted
>> 	method had an individual piece of code in the header to load the
>> 	appropriate registers from locals and the jump to the OSR entry
>> 	point. This is changed so the the OSR caller (the interpreter), uses
>> 	the 'regusage' array in the JIT header to load the correct registers
>> 	and then just jumps directly to the entry point in the method.
>> 	Saving is 24 bytes per method.
>>
>> - Backwards branch targets now doubleword aligned.
>>
>> 	Pads with no ops before a backwards branch target to ensure backwards
>> 	branch target is 64 bit aligned. Small performance benefit.
>>
>> - Addition of OSPACE flag
>>
>> 	Setting environment variable T2_OSPACE will cause the JIT to optimise
>> 	for space as opposed to time. OSPACE does the following.
>>
>> 	o Tweaks the register allocation to allocate register based on space
>> 	o Enables tailing of returns. IE does a branch to the return.
>> 	o Disables doubleword alignment of backwards branch targets
>> 	o Disables inlining invoke virtual/static/special wrappers
>>
>> 	OSPACE has a small performance effect on benchmarks (~10% on ECM) but
>> 	has no noticeable effect on large applications.
>>
>> 	Default is compile for time (OSPACE disabled)
>>
>> - Removed a pass from the compiler
>>
>> 	The JIT had an additional pass to detect 'zombie' code (ie code which
>> 	could be, but has never been called). Zombie code removal was
>> 	disabled in prior versions because it was unreliable, however the
>> 	additional pass was still there.
>>
>> - Removed vestigal and debug code
>>
>> 	Removed #if 0 code and debug code which was no longer functional
>>   
>>     
>