[Bug 81150] [SNB]Piglit spec_arb_shading_language_packing_execution_built-in-functions_fs-packSnorm4x8 fails

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=81150

--- Comment #2 from Neil Roberts <neil at linux.intel.com> ---
Created attachment 104307
  --> https://bugs.freedesktop.org/attachment.cgi?id=104307&action=edit
Simpler test case

This bug is pretty strange. It seems to be related to uploading unsigned int
uniforms. One of the tests tries to upload the value 2139193217 (which is
0x7f817f81). For some inexplicable reason this appears to end up in the shader
as 0x7fc17f81, but only if you build with -O3.

I'm attaching a simpler test case which demonstrates it. It has a fragment
shader with an unsigned int uniform and renders the four bytes of the uniform
to a floating-point texture. It then prints out the values. You can specify an
alternative test value as a command line argument.

It seems to be something very specific about having 0x7f in the
most-significant 8 bits. 0x80, 0x6f or 0x8f work fine.

I am replicating this on a 32-bit build on SandyBridge. It doesn't happen on a
64-bit build with Haswell, but I'm not sure whether it's the SandyBridge or the
32-bit that's important.

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