Replace long sequences of popq with a Drop(int) macro instruction.

Replace long sequences of popq with a Drop(int) macro instruction.

This is for now only done on x64.
Committed: https://code.google.com/p/dart/source/detail?r=7668

[srdjan, 2012-05-15 19:52:27]

LGTM with comments

https://chromiumcodereview.appspot.com/10383189/diff/1/vm/assembler_x64.cc
File vm/assembler_x64.cc (right):

https://chromiumcodereview.appspot.com/10383189/diff/1/vm/assembler_x64.cc#ne...
vm/assembler_x64.cc:1271: addq(RSP, Immediate(stack_elements * kWordSize));
When is an addq better than pop? Maybe add a TODO(fschneider)?

https://chromiumcodereview.appspot.com/10383189/diff/1/vm/assembler_x64.cc#ne...
vm/assembler_x64.cc:1272: }
ASSERT stack_elements >= 0?

https://chromiumcodereview.appspot.com/10383189/diff/1/vm/assembler_x64.h
File vm/assembler_x64.h (right):

https://chromiumcodereview.appspot.com/10383189/diff/1/vm/assembler_x64.h#new...
vm/assembler_x64.h:492: void Drop(int stack_elements);
Use intptr_t

[Florian Schneider, 2012-05-15 21:40:56]

https://chromiumcodereview.appspot.com/10383189/diff/1/vm/assembler_x64.cc
File vm/assembler_x64.cc (right):

https://chromiumcodereview.appspot.com/10383189/diff/1/vm/assembler_x64.cc#ne...
vm/assembler_x64.cc:1271: addq(RSP, Immediate(stack_elements * kWordSize));
On 2012/05/15 19:52:27, srdjan wrote:
> When is an addq better than pop? Maybe add a TODO(fschneider)?

Not sure what is considered better: For i<4 pop is smaller, but always involves
a memory operation, whereas addq is only an ALU operation.

https://chromiumcodereview.appspot.com/10383189/diff/1/vm/assembler_x64.cc#ne...
vm/assembler_x64.cc:1272: }
On 2012/05/15 19:52:27, srdjan wrote:
> ASSERT stack_elements >= 0?

Done.

https://chromiumcodereview.appspot.com/10383189/diff/1/vm/assembler_x64.h
File vm/assembler_x64.h (right):

https://chromiumcodereview.appspot.com/10383189/diff/1/vm/assembler_x64.h#new...
vm/assembler_x64.h:492: void Drop(int stack_elements);
On 2012/05/15 19:52:27, srdjan wrote:
> Use intptr_t

Done.

[siva, 2012-05-15 21:58:59]

https://chromiumcodereview.appspot.com/10383189/diff/6001/vm/assembler_x64.h
File vm/assembler_x64.h (right):

https://chromiumcodereview.appspot.com/10383189/diff/6001/vm/assembler_x64.h#...
vm/assembler_x64.h:492: void Drop(intptr_t stack_elements);
Why call it Drop and not PopElements which seems more readable?

[regis, 2012-05-15 22:12:45]

https://chromiumcodereview.appspot.com/10383189/diff/6001/vm/assembler_x64.h
File vm/assembler_x64.h (right):

https://chromiumcodereview.appspot.com/10383189/diff/6001/vm/assembler_x64.h#...
vm/assembler_x64.h:492: void Drop(intptr_t stack_elements);
On 2012/05/15 21:58:59, asiva wrote:
> Why call it Drop and not PopElements which seems more readable?

I agree with Siva. Also, stack_elements does not evoke a count or number.
PopqN(int n), PopWords(int word_count), PopElements(int num_elements), etc...
would all be preferable.
I am not sure an intptr_t is necessary either.
Just giving a hard time to Florian on his first commit :-)

[Florian Schneider, 2012-05-15 22:36:28]

On 2012/05/15 22:12:45, regis wrote:
> https://chromiumcodereview.appspot.com/10383189/diff/6001/vm/assembler_x64.h
> File vm/assembler_x64.h (right):
> 
>
https://chromiumcodereview.appspot.com/10383189/diff/6001/vm/assembler_x64.h#...
> vm/assembler_x64.h:492: void Drop(intptr_t stack_elements);
> On 2012/05/15 21:58:59, asiva wrote:
> > Why call it Drop and not PopElements which seems more readable?
> 
> I agree with Siva. Also, stack_elements does not evoke a count or number.
> PopqN(int n), PopWords(int word_count), PopElements(int num_elements), etc...
> would all be preferable.
> I am not sure an intptr_t is necessary either.
> Just giving a hard time to Florian on his first commit :-)

I'm fine with Drop(int n) which still concise and different enough from Pop to
indicate that it does something else.