http: simplify isInvalidPath

[starkwang]

The loop unrolling here shows no performance benefits in V8 6.3 any longer, so we can get rid of it. This PR is to simplify isInvalidPath without obvious performance regression.

                                               improvement confidence    p.value
 http/create-clientrequest.js n=1000000 len=1       -3.06 %          * 0.03418092
 http/create-clientrequest.js n=1000000 len=128      0.20 %            0.88729859
 http/create-clientrequest.js n=1000000 len=16      -0.50 %            0.66812482
 http/create-clientrequest.js n=1000000 len=32       2.21 %            0.06679157
 http/create-clientrequest.js n=1000000 len=64      -0.06 %            0.95083016
 http/create-clientrequest.js n=1000000 len=8       -0.61 %            0.49496794

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• tests and/or benchmarks are included
• commit message follows commit guidelines

Affected core subsystem(s)

http

[apapirovski]

Could you confirm whether this applies to V8 6.2 or 6.3? The latter just landed on master and I'm pretty sure the unrolled version was faster on 6.2.

[starkwang]

@apapirovski Sorry for my careless mistake, the benchmark above is based on V8 6.3.292

[starkwang]

Another benchmark result after rebasing from the latest master:

                                               improvement confidence   p.value
 http/create-clientrequest.js n=1000000 len=1        0.11 %            0.8811138
 http/create-clientrequest.js n=1000000 len=128      0.09 %            0.8854386
 http/create-clientrequest.js n=1000000 len=16      -0.19 %            0.7372795
 http/create-clientrequest.js n=1000000 len=32       0.58 %            0.1907908
 http/create-clientrequest.js n=1000000 len=64       1.15 %            0.1873734
 http/create-clientrequest.js n=1000000 len=8       -0.45 %            0.5272168

[apapirovski]

Ok, thanks. I think this might not work well on V8 6.2 but also there's this PR that might get rid of that function all together: #16237 — I'm not sure what the situation around it is (that change is potentially breaking, although it fixes a bug) so that's something to keep in mind.

[BridgeAR]

I guess #16237 is going to land soon. In general it is still good to know that loop unrolling is from now on not needed anymore!

I just added the dont-land-on-v8.x label to make sure it will not be backported in case it will land.

[starkwang]

Closed due to #16237