Implement bitLength intrinsic on x64.

Implement bitLength intrinsic on x64.

R=johnmccutchan@google.com

Committed: https://code.google.com/p/dart/source/detail?r=43126

[srdjan, 2015-01-23 21:30:49]

srdjan@google.com changed reviewers:
+ zra@google.com

[srdjan, 2015-01-23 22:00:52]

srdjan@google.com changed reviewers:
+ johnmccutchan@google.com
- zra@google.com

[Cutch, 2015-01-23 22:10:00]

lgtm

https://codereview.chromium.org/867383002/diff/1/runtime/vm/assembler_x64_tes...
File runtime/vm/assembler_x64_test.cc (right):

https://codereview.chromium.org/867383002/diff/1/runtime/vm/assembler_x64_tes...
runtime/vm/assembler_x64_test.cc:623: __ movq(RCX, Immediate(42));
Good catch.

[srdjan, 2015-01-23 22:41:11]

Committed patchset #1 (id:1) manually as r43126 (presubmit successful).

[Lasse Reichstein Nielsen, 2015-01-25 11:26:52]

lrn@google.com changed reviewers:
+ lrn@google.com

[Lasse Reichstein Nielsen, 2015-01-25 11:26:53]

https://codereview.chromium.org/867383002/diff/1/runtime/vm/intrinsifier_x64.cc
File runtime/vm/intrinsifier_x64.cc (right):

https://codereview.chromium.org/867383002/diff/1/runtime/vm/intrinsifier_x64....
runtime/vm/intrinsifier_x64.cc:801: __ sarq(RCX, Immediate(63));  // All 0 or
all 1.
If you shift RAX instead of RCX here, would the dependecy depth drop by one?

[srdjan, 2015-01-26 18:43:18]

https://codereview.chromium.org/867383002/diff/1/runtime/vm/intrinsifier_x64.cc
File runtime/vm/intrinsifier_x64.cc (right):

https://codereview.chromium.org/867383002/diff/1/runtime/vm/intrinsifier_x64....
runtime/vm/intrinsifier_x64.cc:801: __ sarq(RCX, Immediate(63));  // All 0 or
all 1.
On 2015/01/25 11:26:53, Lasse Reichstein Nielsen wrote:
> If you shift RAX instead of RCX here, would the dependecy depth drop by one?

Thanks for the comment. In theory yes, but with Intel's register renaming, it
should not matter, AFAIK.
Will change it once I tackle MIPS and ARM implementations as well.