X64: Port optimization of LMulI to x64.

X64: Port optimization of LMulI to x64.

Committed: http://code.google.com/p/v8/source/detail?r=7248

[William Hesse, 2011-03-17 12:55:06]

LGTM.

http://codereview.chromium.org/6701003/diff/2001/src/x64/lithium-codegen-x64.cc
File src/x64/lithium-codegen-x64.cc (right):

http://codereview.chromium.org/6701003/diff/2001/src/x64/lithium-codegen-x64....
src/x64/lithium-codegen-x64.cc:873: } else if (right_value == 0) {
If BailoutOnMinusZero is true, we always bail out if a constant right_value is
0, after doing a lot of work.  Maybe we should only bail out if the left value
is negative, and do so immediately, in special case code.

[Lasse Reichstein, 2011-03-17 18:11:54]

http://codereview.chromium.org/6701003/diff/2001/src/x64/lithium-codegen-x64.cc
File src/x64/lithium-codegen-x64.cc (right):

http://codereview.chromium.org/6701003/diff/2001/src/x64/lithium-codegen-x64....
src/x64/lithium-codegen-x64.cc:873: } else if (right_value == 0) {
Yes, I noticed too that we bail out even if we don't know if the left-hand side
is negative.
I decided to keep it for now, under the assumption that if you are multiplying
by a constant zero, you are either doing something incredibly stupid or
something incredibly clever, but I won't try too hard to save a few bytes.
I'll fix it so we don't deoptimize on multiplying a positive value by constant
zero in another CL.