This makes a small change to the Math.pow runtime code to check if the exponent is 0.5 or -0.5. In such cases, it calls sqrt (or 1.0/sqrt) instead of pow. This speeds up Sunspider's partial-sums on my laptop by about 10%.

Here's the actual patch.

Could you please also add this to the traceable native? (same file, search for pow)

Did as Andreas suggested. Speedup with the tracer running is ~20% on partial-sums.

oop, different bug

SQRTPD xmm1,xmm2/m128 we should use that for sqrt and also for this pow special case.

Rockin! /be

SQRTPD is 2x faster than FSQRT, which libc seems to use. Also, we can special case on trace for the -0.5 there.

(In reply to comment #8) > SQRTPD is 2x faster than FSQRT, which libc seems to use. Also, we can special > case on trace for the -0.5 there. I did a few benchmarks and I don't think it's worth the trouble. 1. I compared the performance of SQRTSD (the scalar version of SQRTPD) to FSQRT in the following loop: for (i=1..100000) { x += 1.0/sqrt(i); }. The SQRTSD version was 20% faster. 2. I translated the partial-sums benchmark to C and compiled it with gcc, comparing an SSE2 version to an x87 version. The x87 version was actually a little faster, although I don't know why. Take this all with a grain of salt since my laptop has a pretty lame FPU. But then, lots of people have laptops.

Comment on attachment 462559 [details] [diff] [review] Patch for traceable native as well This is a small but clear win. Let's not get bogged down in the asm; I suggest filing a follow-up bug for that. Any objections to my r+?

r=me

Does this just need to get landed at this point? Did it fall through the cracks?

Sorry, this change got folded in with bug 564548, which optimized pow in a different way.