Add support for near labels....

Add support for near labels.

This change introduces near labels in the assembler, allowing us to
uptimize forward jumps (conditional and unconditional) if we can
guarantee that the jump is witin range -128 to +127.

I changed a large fractions of the existing Labels to NearLabels, and
left out cases where it was not immediately clear if it could be used
or not (not immediately clear means labels covering a large code
block, or used in function calls which we could potentially change to
accept near labels). 


Committed: http://code.google.com/p/v8/source/detail?r=5460

[Søren Thygesen Gjesse, 2010-09-15 10:38:20]

Drive by comment

http://codereview.chromium.org/3388004/diff/1/2
File src/assembler.h (right):

http://codereview.chromium.org/3388004/diff/1/2#newcode100
src/assembler.h:100: class NearLabel BASE_EMBEDDED {
How about adding a type to the Label class

class Label ...

  enum LabelType {
    kTypeFar = ;
    kTypeNear = ;
    ...
  }


  Label(LabelType type = kTypeFar)

  ...

  LabelType type_;
}

the NearLabel class could then inherit from Label and construct a Label with
type kTypeNear. Then the following two lines would achieve the same:

Label label(Label::kTypeNear)
NearLabel label

[fschneider, 2010-09-15 11:21:08]

LGTM.

http://codereview.chromium.org/3388004/diff/1/10
File src/x64/full-codegen-x64.cc (right):

http://codereview.chromium.org/3388004/diff/1/10#newcode681
src/x64/full-codegen-x64.cc:681: Label slow_case;
Indentation off. I think this can be a NearLabel too.

[Rico, 2010-09-15 11:33:29]

I will refactor the NearLabel class in another change.

http://codereview.chromium.org/3388004/diff/1/10
File src/x64/full-codegen-x64.cc (right):

http://codereview.chromium.org/3388004/diff/1/10#newcode681
src/x64/full-codegen-x64.cc:681: Label slow_case;
On 2010/09/15 11:21:08, fschneider wrote:
> Indentation off. I think this can be a NearLabel too.
Actually no, JumpIfNotBothSmi takes a Label