X64: Made simpler version of fast-smi-loop code.

X64: Made simpler version of fast-smi-loop code. 
It avoids the overflow check on the increment.

[Mads Ager (chromium), 2010-07-01 11:49:21]

LGTM

Is this done on the other platforms?

http://codereview.chromium.org/2835030/diff/1/2
File src/x64/codegen-x64.cc (right):

http://codereview.chromium.org/2835030/diff/1/2#newcode1648
src/x64/codegen-x64.cc:1648: loop.set_direction(JumpTarget::BIDIRECTIONAL);
I think you can do this in the constructor?

JumpTarget loop(JumpTarget::BIDIRECTIONAL);

http://codereview.chromium.org/2835030/diff/1/2#newcode1649
src/x64/codegen-x64.cc:1649:
node->break_target()->set_direction(JumpTarget::FORWARD_ONLY);
Do you need to explicitly set the direction for these two? The default is
FORWARD_ONLY.

http://codereview.chromium.org/2835030/diff/1/2#newcode1679
src/x64/codegen-x64.cc:1679: {
Why the extra scope?

[Lasse Reichstein, 2010-07-01 11:58:01]

Not yet on other platforms.
Let's see how much this buys first.

http://codereview.chromium.org/2835030/diff/1/2
File src/x64/codegen-x64.cc (right):

http://codereview.chromium.org/2835030/diff/1/2#newcode1648
src/x64/codegen-x64.cc:1648: loop.set_direction(JumpTarget::BIDIRECTIONAL);
Done.

http://codereview.chromium.org/2835030/diff/1/2#newcode1649
src/x64/codegen-x64.cc:1649:
node->break_target()->set_direction(JumpTarget::FORWARD_ONLY);
Fixed.

http://codereview.chromium.org/2835030/diff/1/2#newcode1679
src/x64/codegen-x64.cc:1679: {
No longer for any reason. There used to be a local variable.
Removed.

[William Hesse, 2010-07-14 14:42:42]

This has an error that was fixed in r5069.  The loop index needs to be taken
from the slot, the register spilled, incremented, and the modified value written
back to the slot.