[WHLSL] Enumerate which operations require uniform control flow and dynamically uniform expressions

[litherum]

Migrated from https://bugs.webkit.org/show_bug.cgi?id=189122:

At 2018-08-29T23:35:44Z, [email protected] wrote:
Indexing into an array of textures requires a dynamically uniform expression
sample() involves an implicit derivative, and so requires uniform control flow

[litherum]

At 2018-09-13T01:50:46Z, [email protected] wrote:
rdar://problem/44402999

[litherum]

At 2018-09-23T06:51:38Z, [email protected] wrote:
The following functions require uniform control flow:

ddx()
ddy()
AllMemoryBarrierWithGroupSync()
DeviceMemoryBarrierWithGroupSync()
GroupMemoryBarrierWithGroupSync()
Sample()
SampleBias()
Gather()
GatherRed()
GatherGreen()
GatherBlue()
GatherAlpha()
SampleCmp()
GatherCmp()
GatherCmpRed()
GatherCmp()
GatherCmpRed()

[litherum]

At 2018-09-23T06:52:57Z, [email protected] wrote:
Indexing into an array which contains textures requires dynamically uniform expressions. I think that's the only operation.

[litherum]

At 2018-09-23T06:54:08Z, [email protected] wrote:
I suppose this is done now.