[webgl] Fix uninitialized zeros tensors, fix dtype upcasting.

[annxingyuan]

This fixes the nightly build error.

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This change is 

[pyu10055]

Reviewable status: complete! 1 of 1 approvals obtained (waiting on @annxingyuan, @pyu10055, and @tafsiri)

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tfjs-backend-webgl/src/kernels/Cast.ts, line 76 at r1 (raw file):

  if (dtype === 'bool') {
    const zerosTensorInfo = backend.makeTensorInfo(
        [], 'bool', util.getTypedArrayFromDType('bool', 1));

I think typed array allow zero length, why the length needs to be set to 1 here?

[pyu10055]

Reviewed 3 of 3 files at r1.
Reviewable status: complete! 1 of 1 approvals obtained (waiting on @annxingyuan, @pyu10055, and @tafsiri)

[pyu10055]

Thanks for fixing the nightly build!

Reviewable status: complete! 1 of 1 approvals obtained (waiting on @annxingyuan, @pyu10055, and @tafsiri)

[annxingyuan]

Reviewable status: complete! 1 of 1 approvals obtained (waiting on @pyu10055 and @tafsiri)

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tfjs-backend-webgl/src/kernels/Cast.ts, line 76 at r1 (raw file):

Previously, pyu10055 (Ping Yu) wrote…

I think typed array allow zero length, why the length needs to be set to 1 here?

We need to actually upload the value 0 to the GPU so that we can check whether the input equals 0 as part of casting to bool. The reason this only fails in nightly is because for PR's our threshold for uploading values as textures as opposed to uniforms is 0 (so everything is uploaded as a texture). If we print a zero length typed array to a texture (or even if we print null to a texture), it will be sampled as 0, so tests pass. However there is a difference between uploading 0 as a uniform, and uploading an empty typed array as a uniform.

[pyu10055]

The test of concat a large number of tensors is still timing out in the latest nightly build:

Chrome 77.0.3865 (Windows 10.0.0) concat3d webgl2 {"WEBGL_VERSION":2,"WEBGL_CPU_FORWARD":false,"WEBGL_SIZE_UPLOAD_UNIFORM":0} concat a large number of tensors, axis=1 FAILED
	Error: Timeout - Async callback was not invoked within timeout specified by jasmine.DEFAULT_TIMEOUT_INTERVAL.
	    at <Jasmine>
Chrome 77.0.3865 (Windows 10.0.0) SLOW 5.288 secs: concat3d webgl2 {"WEBGL_VERSION":2,"WEBGL_CPU_FORWARD":false,"WEBGL_SIZE_UPLOAD_UNIFORM":0} concat a large number of tensors, axis=1
Chrome 77.0.3865 (Windows 10.0.0) SLOW 5.288 secs: concat3d webgl2 {"WEBGL_VERSION":2,"WEBGL_CPU_FORWARD":false,"WEBGL_SIZE_UPLOAD_UNIFORM":0} concat a large number of tensors, axis=1