Faster comparison of identical objects.

Faster comparison of identical objects.

Committed: http://code.google.com/p/v8/source/detail?r=4391

[antonm, 2010-04-12 07:17:33]

Mads, Vitaly,

may you have a look?

[Vitaly Repeshko, 2010-04-12 07:37:45]

LGTM.

Before submitting please double-check we have all interesting cases covered by
our tests.


-- Vitaly

http://codereview.chromium.org/1558040/diff/1/2
File src/ia32/codegen-ia32.cc (right):

http://codereview.chromium.org/1558040/diff/1/2#newcode11060
src/ia32/codegen-ia32.cc:11060: static int NanComparisionResult(Condition cc) {
nit: In other places (constant name) it's NaN.

http://codereview.chromium.org/1558040/diff/1/2#newcode11075
src/ia32/codegen-ia32.cc:11075: // for Nan and undefined.
nit: NaN.

http://codereview.chromium.org/1558040/diff/1/2#newcode11082
src/ia32/codegen-ia32.cc:11082: // Check for undefined.
It might help to have a short summary of undefined comparison rules here:
undefined == undefined, but not undefined <= undefined, etc.

http://codereview.chromium.org/1558040/diff/1/2#newcode11095
src/ia32/codegen-ia32.cc:11095: __ Set(eax, Immediate(0));
Use Smi::FromInt(EQUAL) instead of 0.

http://codereview.chromium.org/1558040/diff/1/2#newcode11102
src/ia32/codegen-ia32.cc:11102: Immediate(Factory::heap_number_map()));
nit: Indent.

http://codereview.chromium.org/1558040/diff/1/2#newcode11127
src/ia32/codegen-ia32.cc:11127: __ setcc(above_equal, eax);
ASSERT(1 != EQUAL).

[Mads Ager (chromium), 2010-04-12 10:25:36]

LGTM

http://codereview.chromium.org/1558040/diff/1/2
File src/ia32/codegen-ia32.cc (right):

http://codereview.chromium.org/1558040/diff/1/2#newcode11060
src/ia32/codegen-ia32.cc:11060: static int NanComparisionResult(Condition cc) {
It seems you should give this a more general name.  You really use this to get
the negative result for both 'undefined' and 'NaN'.

[antonm, 2010-04-12 15:00:03]

Thanks a lot, gentlemen.

@Vitaly: yes, we have: test/mjsunit/regress/regress-503.js and
t/m/compare-nan.js.  Plus I hope Sputnik would catch any harm I might have
produced.

http://codereview.chromium.org/1558040/diff/1/2
File src/ia32/codegen-ia32.cc (right):

http://codereview.chromium.org/1558040/diff/1/2#newcode11060
src/ia32/codegen-ia32.cc:11060: static int NanComparisionResult(Condition cc) {
On 2010/04/12 10:25:36, Mads Ager wrote:
> It seems you should give this a more general name.  You really use this to get
> the negative result for both 'undefined' and 'NaN'.

Renamed to NegativeComparisonResult

http://codereview.chromium.org/1558040/diff/1/2#newcode11075
src/ia32/codegen-ia32.cc:11075: // for Nan and undefined.
On 2010/04/12 07:37:45, Vitaly wrote:
> nit: NaN.

Done.

http://codereview.chromium.org/1558040/diff/1/2#newcode11082
src/ia32/codegen-ia32.cc:11082: // Check for undefined.
On 2010/04/12 07:37:45, Vitaly wrote:
> It might help to have a short summary of undefined comparison rules here:
> undefined == undefined, but not undefined <= undefined, etc.

Done.

http://codereview.chromium.org/1558040/diff/1/2#newcode11095
src/ia32/codegen-ia32.cc:11095: __ Set(eax, Immediate(0));
On 2010/04/12 07:37:45, Vitaly wrote:
> Use Smi::FromInt(EQUAL) instead of 0.

Done.

http://codereview.chromium.org/1558040/diff/1/2#newcode11102
src/ia32/codegen-ia32.cc:11102: Immediate(Factory::heap_number_map()));
On 2010/04/12 07:37:45, Vitaly wrote:
> nit: Indent.

Done.

http://codereview.chromium.org/1558040/diff/1/2#newcode11127
src/ia32/codegen-ia32.cc:11127: __ setcc(above_equal, eax);
On 2010/04/12 07:37:45, Vitaly wrote:
> ASSERT(1 != EQUAL).

Done.