Implement packed clipping op.

[annxingyuan]

This PR addresses tensorflow/tfjs#803

Changes

• Added ClipPackedProgram that implements clipping for packed textures
• Added ENV flag WEBGL_PACK_CLIP, defaults to false
• Added ENV flag WEBGL_PACK, defaults to false, that turns all packing-related flags on or off
• Turn off NaN checking if PROD flag is on
• Support scalar sampling in packed ops
• Partially support packed get${Var}AtOutCoords and broadcasting - broadcasting only occurs when the innermost dimensions are the same and the vector to be broadcast is rank 0 or 1.

PERF

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This change is 

[nsthorat]

Reviewed 8 of 9 files at r1.
Reviewable status: 0 of 1 approvals obtained (waiting on @annxingyuan, @nsthorat, and @dsmilkov)

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src/kernels/webgl/shader_compiler.ts, line 325 at r2 (raw file):

} else {
  /*
  Previous NaN check '(val < 0.0 || 0.0 < val || val == 0.0) ? false : true'

use * on each line

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src/kernels/webgl/shader_compiler.ts, line 335 at r2 (raw file):

    bool hasNaN(vec4 values) {
      return any(bvec4(
        (values.x < 1.0 || 0.0 < values.x || values.x == 0.0) ? false : true,

can you call isNaN for each of these?

[annxingyuan]

Reviewable status: complete! 1 of 1 approvals obtained (waiting on @dsmilkov)

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src/kernels/webgl/shader_compiler.ts, line 325 at r2 (raw file):

Previously, nsthorat (Nikhil Thorat) wrote…

use * on each line

Done

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src/kernels/webgl/shader_compiler.ts, line 335 at r2 (raw file):

Previously, nsthorat (Nikhil Thorat) wrote…

can you call isNaN for each of these?

Done

[astojilj]

Minor issue: might be useful to note that this won't work if trying to turn on packing by calling set('WEBGL_PACK', true) from application code; it is still required to call set('WEBGL_LAZILY_UNPACK', true) since tf-layers initialization evaluates ENV.get('EPSILON') before application code, and causes evaluating and setting WEBGL_LAZILY_UNPACK to false.
I'm aware that this should be done, properly, using URL query string parameters.

Call stack:
Environment.evaluateFeature (environment.ts:299)
Environment.get (environment.ts:270)
MathBackendWebGL.compileAndRun (backend_webgl.ts:1988)
MathBackendWebGL.abs (backend_webgl.ts:1396)
(anonymous) (backend_webgl.ts:2029)
(anonymous) (engine.ts:156)
Engine.scopedRun (engine.ts:167)
Engine.tidy (engine.ts:153)
Environment.tidy (environment.ts:186)
MathBackendWebGL.floatPrecision (backend_webgl.ts:2028)
Environment.evaluateFeature (environment.ts:368)
Environment.get (environment.ts:270)
(anonymous) (common.ts:15)
extendStatics (tf-layers.js:20)
(anonymous) (tf-layers.js:21)

[annxingyuan]

Hey @astojilj - that's a good point - could you create a separate PR for this change?

[astojilj]

Hey @astojilj - that's a good point - could you create a separate PR for this change?

I reported this so that you are aware of it when testing. Otherwise, I'm not sure what would be the desired behavior - setting master switch WEBGL_PACK would override all previously set sub-flags?