Validator should not check for capability when seeing decorations of ClipDistance, CullDistance, or PointSize

[chrisforbes]

See KhronosGroup/Vulkan-LoaderAndValidationLayers#858, KhronosGroup/glslang#472.

[johnkslang]

I fixed the title, as this should not be generalized beyond ClipDistance, CullDistance, and PointSize.

[dneto0]

I made that change to the validator on July 7:
06581f5

But it's conditioned on using a Vulkan 1.0 context, since it was a Vulkan decision to relax that rule.
@chrisforbes Please confirm that you have code at least as fresh as that.

The master branch of the Vulkan layers tree specifies revision 6c61bf2 from July 22 which should be fresh enough. And its only call to spvContextCreate does use SPV_ENV_VULKAN_1_0.

[dneto0]

Commented on the layers bug suggesting that maybe the command line tool was not being used, and that you should use --target-env vulkan1.0 option.

[johnkslang]

What situation should error on ClipDistance (et. al.) Decoration with no capability? I don't think there is one; rather the validator should unconditionally tolerate ClipDistance/CullDistance/PointSize decoration, and not require specific options be specified to do so.

[dneto0]

The basic rule applied is any mention of an enum that lists a required capability may only be in a module that declares that capability. That's even as a decoration.
The specific rule that overrides that default is in the Vulkan env spec, which is why the relaxation of the check is only done for Vulkan 1.0 targets.

In particular we now have OpenGL environments in SPIRV-Tools. Almost certainly the same rule override would apply there. Since it's basically the same GLSL variation is going to be used any time ClipDistance (and friends) is to be used, there's a strong argument to say the rule should always be relaxed for ClipDistance, CullDistance, PointSize. I would guess that's your recommendation @johnkslang ?

[johnkslang]

Yes, the exception is driven by whether it is ClipDistance/CullDistance/PointSize, and not driven by what the environment is.

The general rule (decoration requires capability), would also apply universally, unless it was ClipDistance/CullDistance/PointSize.

So, slice along decoration name, not along environment.

[dneto0]

Ok. I'll do that.

[dneto0]

FYI. The previous relaxation was prompted by #261

[dneto0]

FYI. Mention of PointSize as a BuiltIn will still trigger requirement of the Shader capability. Nobody has complained about that yet.

[johnkslang]

So, we need to reopen? That's not to spec.

Note this is all "spirit of the law" as well as now to spec.:

• the point of capability is to declare before utilizing a platform's feature
• decoration does not itself utilize the platform's feature
• ClipDistance/CullDistance/PointSize are special because of cross-linkage rules, in that they may need decoration without subsequent use