libjpeg-turbo not compiling with NEON on iOS?

[Werner Sharp]

When doing some profiling with m87 Skia (the current version we are using), I noticed that JPEG decoding using libjpeg-turbo is not using NEON at all. 

It appears (from long ago) that the NEON source files were disabled on iOS probably from compiler compatibility issues...

https://github.com/google/skia/blob/master/third_party/libjpeg-turbo/BUILD.gn

} else if (current_cpu == "arm64" && !is_mac && !is_ios && !is_win) {

sources += [

"../externals/libjpeg-turbo/simd/arm/arm64/jsimd.c",

"../externals/libjpeg-turbo/simd/arm/arm64/jsimd_neon.S",

"../externals/libjpeg-turbo/simd/arm/common/jcsample-neon.c",

"../externals/libjpeg-turbo/simd/arm/common/jdcolor-neon.c",

"../externals/libjpeg-turbo/simd/arm/common/jdmerge-neon.c",

"../externals/libjpeg-turbo/simd/arm/common/jdsample-neon.c",

"../externals/libjpeg-turbo/simd/arm/common/jidctfst-neon.c",

"../externals/libjpeg-turbo/simd/arm/common/jidctint-neon.c",

"../externals/libjpeg-turbo/simd/arm/common/jidctred-neon.c",

]

}

Removing the "!is_ios" check still compiles fine and JPEG decoding is about 2x faster on my test case and shows NEON usage. in the profiler.

Is this a change that can be made in Skia please?

Thank you.

[Mike Klein]

We generally don't suggest using things in third_party/externals for reasons like this.  It's kind of just what we happen to be testing against.

But yeah, might as well...

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[Mike Klein]

I've got this going at https://skia-review.googlesource.com/c/skia/+/364498, and it's looking promising.

(We turned this off in https://skia-review.googlesource.com/c/skia/+/4755/ ~4 years ago when it wouldn't compile.)

[Werner Sharp]

Thanks for trying this out so quick!

[Mike Klein]

Oh you bet.

That change landed, and the CI tree looks pretty happy about it, so I think it's likely to stick.

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