ARM64: Clean up LiveEdit.

ARM64: Clean up LiveEdit.

BUG=
R=yangguo@chromium.org

Committed: https://code.google.com/p/v8/source/detail?r=21957

[loislo, 2014-06-23 17:37:06]

+alph

[jbramley, 2014-06-23 17:49:06]

On 2014/06/23 17:37:06, loislo wrote:
> +alph

Oops, sorry!

I should probably explain a bit too.

  - The smis moved into 'scratch' at the start can be loaded with a
    single instruction. There's no need to use ldr for these. (This
    should also be true on ARM, actually.)

  - ARM64 has a funny stack interface because the architectural stack
    pointer (csp) has inconvenient alignment restrictions. As a result,
    every 'Push' has an overhead.
    - PushMultipleTimes is a direct replacement for the 'push' loop.
    - masm->StackPointer() abstracts jssp. (It's irrelevant in this
      case, but in some places masm->StackPointer() could return csp.
      This change is just for consistency.)
    - AssertStackConsistency() makes sure that we haven't done something
      silly. In particular, it makes sure that jssp >= csp at all times.
      This helps to enforce ABI requirements about accesses below the
      stack pointer.

  - The ARM64 MacroAssembler uses ip0 and ip1 as scratch registers, but
    we have a mechanism for claiming them for other purposes. This
    ensures that they are used safely, so we don't have to worry about
    the MacroAssembler clobbering our temporary values.

  - You can store xzr directly; there's no need to move it to x1 first.

  - The ARM64 back-end generally uses 'Br' to branch to a register. I
    don't really know why 'Jump(Register)' exists.

[Yang, 2014-06-24 08:04:59]

On 2014/06/23 17:49:06, jbramley wrote:
> On 2014/06/23 17:37:06, loislo wrote:
> > +alph
> 
> Oops, sorry!
> 
> I should probably explain a bit too.
> 
>   - The smis moved into 'scratch' at the start can be loaded with a
>     single instruction. There's no need to use ldr for these. (This
>     should also be true on ARM, actually.)
> 
>   - ARM64 has a funny stack interface because the architectural stack
>     pointer (csp) has inconvenient alignment restrictions. As a result,
>     every 'Push' has an overhead.
>     - PushMultipleTimes is a direct replacement for the 'push' loop.
>     - masm->StackPointer() abstracts jssp. (It's irrelevant in this
>       case, but in some places masm->StackPointer() could return csp.
>       This change is just for consistency.)
>     - AssertStackConsistency() makes sure that we haven't done something
>       silly. In particular, it makes sure that jssp >= csp at all times.
>       This helps to enforce ABI requirements about accesses below the
>       stack pointer.
> 
>   - The ARM64 MacroAssembler uses ip0 and ip1 as scratch registers, but
>     we have a mechanism for claiming them for other purposes. This
>     ensures that they are used safely, so we don't have to worry about
>     the MacroAssembler clobbering our temporary values.
> 
>   - You can store xzr directly; there's no need to move it to x1 first.
> 
>   - The ARM64 back-end generally uses 'Br' to branch to a register. I
>     don't really know why 'Jump(Register)' exists.

lgtm.

[Yang, 2014-06-24 08:05:00]

On 2014/06/23 17:49:06, jbramley wrote:
> On 2014/06/23 17:37:06, loislo wrote:
> > +alph
> 
> Oops, sorry!
> 
> I should probably explain a bit too.
> 
>   - The smis moved into 'scratch' at the start can be loaded with a
>     single instruction. There's no need to use ldr for these. (This
>     should also be true on ARM, actually.)
> 
>   - ARM64 has a funny stack interface because the architectural stack
>     pointer (csp) has inconvenient alignment restrictions. As a result,
>     every 'Push' has an overhead.
>     - PushMultipleTimes is a direct replacement for the 'push' loop.
>     - masm->StackPointer() abstracts jssp. (It's irrelevant in this
>       case, but in some places masm->StackPointer() could return csp.
>       This change is just for consistency.)
>     - AssertStackConsistency() makes sure that we haven't done something
>       silly. In particular, it makes sure that jssp >= csp at all times.
>       This helps to enforce ABI requirements about accesses below the
>       stack pointer.
> 
>   - The ARM64 MacroAssembler uses ip0 and ip1 as scratch registers, but
>     we have a mechanism for claiming them for other purposes. This
>     ensures that they are used safely, so we don't have to worry about
>     the MacroAssembler clobbering our temporary values.
> 
>   - You can store xzr directly; there's no need to move it to x1 first.
> 
>   - The ARM64 back-end generally uses 'Br' to branch to a register. I
>     don't really know why 'Jump(Register)' exists.

lgtm.

[jbramley, 2014-06-24 08:16:49]

Committed patchset #1 manually as r21957 (presubmit successful).