Re: [webkit-dev] want to port JIT to MIPS - how to get of SSE2 now?

Gavin Barraclough Thu, 26 Feb 2009 18:14:40 -0800

ALTERNATE_JSIMMEDIATE is only supported on 64-bit, and all 64-bitx86's have SSE2 – so the ALTERNATE_JSIMMEDIATE code is assuming thatSSE2 is present. If we wanted to make ALTERNATE_JSIMMEDIATE beingenabled on 32-bit x86 possible, then we would also need to checkisSSE2Present() here.

To address the problem at a slightly higher level,ENABLE_JIT_OPTIMIZE_ARITHMETIC is intended to guard JIT generation ofdouble precision floating point math. In the long run we willpotentially place double precision operations within the domain of theMacroAssembler interface, but this is unlikely to happen before theJIT is ported to another platform that feature a 64-bit register filebased FPU (which will help drive ensuring that we get the interfaceright).

I would suggest that ENABLE_JIT_OPTIMIZE_ARITHMETIC is not somethinginteresting to worry about at this stage. It only affects a couple offunctions, and shouldn't have any wider ramifications on designdecisions – a sensible approach in porting the JIT is to switch thethree optimizations switches off and then not thinking about themuntil after the ported JIT is up and running. (In fact, that isexactly why these three switches exist – to make it possible to portthe JIT without worrying about some of the hairier bits of codegeneration. These compile switches were added when we ported the JITto x86-64. Only once the JIT was up and running did we switch them onone by one).


cheers,
G.


On Feb 26, 2009, at 5:39 PM, x yz wrote:

yes but if isSSE2Present() returns false the code becomes verysimple so I doubt it may be slow.

what's the benefit to enable/disable ALTERNATE_JSIMMEDIATE?
thanks
joe



--- On Fri, 2/27/09, Gavin Barraclough <barraclo...@apple.com> wrote:

From: Gavin Barraclough <barraclo...@apple.com>

Subject: Re: [webkit-dev] want to port JIT to MIPS - how to get ofSSE2 now?

To: "WebKit Development" <webkit-dev@lists.webkit.org>
Date: Friday, February 27, 2009, 6:03 AM
SSE2 code generation is guarded by calls to a function
'isSSE2Present()'.

On Feb 26, 2009, at 12:27 PM, x yz wrote:


Hi,
Old version seems use ENABLE_JIT_OPTIMIZE_ARITHMETIC

to enable sse2

and only for X86_64, current version changes conf to:
1. you must ENABLE_JIT_OPTIMIZE_ARITHMETIC or else you

use

interpreter for arithmatic.
2. if ALTERNATE_JSIMMEDIATE not enabled you must have

sse2 engine

3. if ALTERNATE_JSIMMEDIATE enabled, you use mmx

arithematic, but

ALTERNATE_JSIMMEDIATE is enabled in paltform.h only

for X86_64 &&

MAC. That means on X86 you need sse2???
thanks for your time!
joe



--- On Sun, 2/22/09, x yz <last...@yahoo.com>

wrote:

From: x yz <last...@yahoo.com>
Subject: Re: [webkit-dev] want to port JIT to MIPS
To: "WebKit Development"

<webkit-dev@lists.webkit.org>, "Gavin

Barraclough" <barraclo...@apple.com>
Date: Sunday, February 22, 2009, 4:34 PM
Thanks a lot otherwise I have misunderstanding.

Yes I'll

do wrec first. I just want to clean up possible

blocking

issues.

I see wrec uses regparm(3) and jit always use

fastcall for

X86?
In JIT.cpp ctiTrampoline put CallFrame in edi, but

how

about other arguments - where are they be

fetched/poped from

stack?

when deal with caller/callee saved regs, gcc MIPS

just

preserves them when necesasary. The problem is

after JIT

used gcc may not have enough knowledge on
"necessary", do we have a way to force

gcc always

preserve
them?

how to identify a patch

(patchimm/patchptr/patchaddr)

relates to a data field in an instruction or

relates to an

element in a data array? In Mips the former means

the 32bit

needs to be separated into two 16bits and patched

into two

instructions. But if a 32bit is a pointer in a

pointer

array, we can save it directly.

rgds
joe


--- On Fri, 2/20/09, Gavin Barraclough
<barraclo...@apple.com> wrote:

From: Gavin Barraclough

<barraclo...@apple.com>

Subject: Re: [webkit-dev] want to port JIT to

MIPS

To: "WebKit Development"

<webkit-dev@lists.webkit.org>

Date: Friday, February 20, 2009, 2:01 PM
On Feb 19, 2009, at 8:27 PM, x yz wrote:

I'd appreaciate your help to clarify

the

problem I

faced:


1.In JIT.cpp I roughly understand

ctiTrampoline()

except for sp-0x1C, I guess the 1C includes 6

argument

yet

the 7th or 1st may be the hidden C++ pointer?

And the

reserved 1C stack space seems not used? why

esi is

forced to

be 512 rather than use input argument?

The JIT allocates a fixed frame on the stack

which is

used

to pass arguments into stub functions.  The

0x1C

contains a

spare word or two to maintain stack alignment.

%esi

is used

in the timeout check mechanism.

2.How to understand the stack balance in

ctiVMThrowTrampoline()? why after calling we

still add

1C

w/o sub 1C before calling? where comes
_ZN3JSC11Interpreter12cti_vm_throwEPPv and how

do I

know

which name for Mips? does this one relates to

variable

argument function call?

ctiVMThrowTrampoline is never called as a

function (it

is

declared as a function only to provide a

symbol that

can be

manipulated from C code).

ctiVMThrowTrampoline is

used in

returning back from JIT generated code, in the

case of

an

exception.

3.I know how to handle jump in Mips, but

not sure

how/when to handle

patchAddress/patchImm/patchPointer

because I'm not sure the instructions

related. I

guess

all patches are for last 32bit IMM field of

instructions.

Mips can't load 32bit in one

instruction,

thus I

need to know the instruction before I can

patch/add in

the

32bit data.


4.I'm kind of want no asm code outside

<assembler> folder, any plan for that?

No.  The assembler is intended to be

independent of

JavaScript types - it's just an assembler.

The

asm

trampolines are specific to the JIT.  It is

currently

the

intention that architecture specific parts of

the JIT

implementation will remain in the jit folder.

I'd suggest that in attempting to port the

jit,

WREC

would be a good place to start.

cheers,
G.


rgds
joe

--- On Mon, 2/16/09, x yz

<last...@yahoo.com>

wrote:

From: x yz <last...@yahoo.com>
Subject: Re: [webkit-dev] want to port

JIT to

MIPS

- when WREC/JIT enabled?

To: "Gavin Barraclough"

<barraclo...@apple.com>

Cc: "WebKit Development"

<webkit-dev@lists.webkit.org>

Date: Monday, February 16, 2009, 5:25

AM

Hi,
from paltform.h it is enabled only on

X86

MAC/WIN;

from

javaScriptCore.pri it is also enabled

for

(QT_ARCH,i386).

But, from config.log I see them are

enabled!


how can I run WREC/JIT test so I can

trace in

X86

asm coce

generated?
thanks a lot.
joe



--- On Sat, 2/7/09, Gavin Barraclough
<barraclo...@apple.com> wrote:

From: Gavin Barraclough

<barraclo...@apple.com>

Subject: Re: [webkit-dev] want to

port

JIT to

MIPS -

using X86::ecx as base

To: last...@yahoo.com
Cc: "WebKit Development"

<webkit-dev@lists.webkit.org>

Date: Saturday, February 7, 2009,

7:08 AM

On Feb 6, 2009, at 2:52 PM, x yz

wrote:

1.what's the meaning of

ALTERNATE_JSIMMEDIATE

and

slow case?

On x86-64 we use a different

implementation of

the

class

JSImmediate.  See JSImmediate.h.
Re 'slow case', in the JIT

code

generation is

performed as two passes over the

bytecode

–

see

JIT::privateCompileMainPass and
JIT::privateCompileSlowCases.

2.how come the following code

can use

ECX

as base

register?

load32(Address(X86::ecx,

FIELD_OFFSET(Structure,

m_typeInfo.m_flags)), X86::ecx);

if the X86::ecx just means its

value

1 in

ModR/M,

does

it means [BX+DI]?

I think you're looking at the

old

16-bit

addressing

mode tables; 32/64-bit x86 can

happily

encode

ecx as a

base

register.  If you're looking

at the

Intel

IA-32

manual

volume 2, see table 2-2 on the

next page.

3. can anybody help me on my

previous

questions?

does

JIT support floating point?

Yes, some.  See JITArithmetic.cpp.

cheers,
G.

_______________________________________________

webkit-dev mailing list
webkit-dev@lists.webkit.org

http://lists.webkit.org/mailman/listinfo.cgi/webkit-dev

_______________________________________________

webkit-dev mailing list
webkit-dev@lists.webkit.org

http://lists.webkit.org/mailman/listinfo.cgi/webkit-dev




_______________________________________________
webkit-dev mailing list
webkit-dev@lists.webkit.org

http://lists.webkit.org/mailman/listinfo.cgi/webkit-dev


_______________________________________________
webkit-dev mailing list
webkit-dev@lists.webkit.org
http://lists.webkit.org/mailman/listinfo.cgi/webkit-dev


_______________________________________________
webkit-dev mailing list
webkit-dev@lists.webkit.org
http://lists.webkit.org/mailman/listinfo.cgi/webkit-dev

Re: [webkit-dev] want to port JIT to MIPS - how to get of SSE2 now?

Reply via email to