[Radar 28902144]
On macOS machines with an Intel Haswell GPU, usamperCube and usamper3D work incorrectly rendering a few wrong pixels to FBO, while other texture formats like float and signed integer have no such problem with exactly same cases.
This bug causes failures of texture{lod | grad | projgrad}.html’s tests in the WebGL 2.0 conformance suite.
This bug does not occur on other GPU types on macOS, nor on other operating systems.


Steps to reproduce:

1. Download Chrome Canary and run from the Terminal:
/Applications/Google\ Chrome\ Canary.app/Contents/MacOS/Google\ Chrome\ Canary --enable-unsafe-es3-apis

2. Check out the KhronosGroup/WebGL repository:
git clone https://github.com/KhronosGroup/WebGL.git

3. Launch an HTTP server against that repository:
cd WebGL
python -m SimpleHTTPServer

4. Navigate the browser to the test cases:
http://localhost:8000/sdk/tests/deqp/functional/gles3/shadertexturefunction/texturelod.html?webglVersion=2&quiet=0
http://localhost:8000/sdk/tests/deqp/functional/gles3/shadertexturefunction/texturegrad.html?webglVersion=2&quiet=0
http://localhost:8000/sdk/tests/deqp/functional/gles3/shadertexturefunction/textureprojgrad.html?webglVersion=2&quiet=0

These tests are also available online at:
http://www.khronos.org/registry/webgl/sdk/tests/deqp/functional/gles3/shadertexturefunction/texturelod.html?webglVersion=2&quiet=0
http://www.khronos.org/registry/webgl/sdk/tests/deqp/functional/gles3/shadertexturefunction/texturegrad.html?webglVersion=2&quiet=0
http://www.khronos.org/registry/webgl/sdk/tests/deqp/functional/gles3/shadertexturefunction/textureprojgrad.html?webglVersion=2&quiet=0


Expected Results:

Expect all tests to pass, as they do on other operating systems and on other GPU types on macOS.


Actual Results:

Some test cases involving usamplercube_vertex, usamplercube_fragment, and usampler3d_fragment fail.


OS X Build/Version:

macOS Sierra (10.12)
MacBook Pro-Mid 2015-Intel Iris Pro Graphics 5200 

Notes:

NOT reproducible on MacBook-Early 2016-Intel HD Graphics 515