X64 implementation: Add high_bit() and low_bits() to register methods.

X64 implementation: Add high_bit() and low_bits() to register methods.

Committed: http://code.google.com/p/v8/source/detail?r=2231

[Lasse Reichstein, 2009-06-22 07:52:46]

LGTM

http://codereview.chromium.org/141032/diff/1/2
File src/x64/assembler-x64.cc (right):

http://codereview.chromium.org/141032/diff/1/2#newcode1197
Line 1197: emit_rex_64(dst);
If REX.W isn't required, we might as well use emit_optional_rex_32(dst)

http://codereview.chromium.org/141032/diff/1/2#newcode1223
Line 1223: emit_rex_64(src);
As above.

http://codereview.chromium.org/141032/diff/1/3
File src/x64/assembler-x64.h (right):

http://codereview.chromium.org/141032/diff/1/3#newcode97
Line 97: int high_bit() const {
We will eventually need this for xmm registers too (mmx registers was a mistake,
and will be removed again).

[William Hesse, 2009-06-22 08:18:32]

http://codereview.chromium.org/141032/diff/1/2
File src/x64/assembler-x64.cc (right):

http://codereview.chromium.org/141032/diff/1/2#newcode1197
Line 1197: emit_rex_64(dst);
On 2009/06/22 07:52:46, Lasse Reichstein wrote:
> If REX.W isn't required, we might as well use emit_optional_rex_32(dst)
> 

It is misleading to the code reader to read rex_32 for an actual 64-bit move. 
Actually, REX without REX.W may be diffrerent than no REX at all.