On 2013/04/09 16:27:52, Yang wrote:
On 2013/04/02 06:44:21, Zheng Liu wrote:
> X64 already had it because I accidentally included it in a previous code
review
> http://code.google.com/p/v8/source/detail?r=13289
> (oops, sorry!)
>
> This change is that for some processor, sequence like:
> divsd XMM0, xmm?
> (movaps XMM0, XMM0)
> mulsd xmm? ,XMM0
>
> Will prevent div and mul execute in parallel even if they are indepedent
(e.g.
> belong to two loop iterations)
> Adding [*anymov* XMM0, XMM0] can workaround it.
>
> I tested it on Nehalem/Westmere (e.g. i7-9**/8**, Xeon X56**)
> Not sure about newer processors.
>
>
> Case to reproduce:
> ~12% faster on affected processors
>
> var darr1 = new Float64Array([0.5, 0.5]);
> var darr2 = new Float64Array([0.5, 0.5]);
>
> function fn1(a, b, n) {
> var c;
> for (var i = 0; i < n; i++)
> c = b[i&1] * (1 / a[i&1]);
> }
>
> fn1(darr1, darr2, 10);
> fn1(darr1, darr2, 10);
> %OptimizeFunctionOnNextCall(fn1);
> var start = Date.now();
> fn1(darr1, darr2, 1000*1000*100);
> print(Date.now() - start);
Sorry that it took this long.
Could you add a comment to the inserted instruction (also on x64) so that
it
makes some sense when somebody looks at the code later on and won't
accidentally
remove it?
Comments addressed.
Please take another look.
https://codereview.chromium.org/13447003/
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