[SPIR-V] HLSL clip is treated as OpKill instead of OpDemoteToHelperInvocation in Vulkan 1.3 or -fspv-extension=SPV_EXT_demote_to_helper_invocation

[danginsburg]

Description
DXC supports generating OpDemoteToHelperInvocation for HLSL discard if using Vulkan 1.3 or -fspv-extension=SPV_EXT_demote_to_helper_invocation. This is correct. But if you use clip(-1) in your shader you will still get OpKill. Is this just a bug?

Steps to Reproduce
https://shader-playground.timjones.io/6c6b28f4a3a9fe0365846aff9b7aa2c7

struct PSInput
{
	float4 color : COLOR;
};

float4 PSMain(PSInput input) : SV_TARGET
{
    // Incorrect: OpKill
    clip(input.color.a < 0 ? -1 : 1);
    // Correct: OpDemoteToHelperInvocation
    //if (input.color.a < 0 )
      //  discard;
	return input.color;
}

Actual Behavior
I think clip should produce the same output as discard?

Environment

• DXC version : Updated from trunk on 2023-06-16
• Host Operating System : N/A

[sudonatalie]

@Keenuts Can you take a look at this?

[s-perron]

Yes, this is a bug, and should be fixed. We should never be generating OpKill.

[jeremy-lunarg]

@s-perron

I believe this issue can be closed. You fixed this in #5970, but I think you referenced the wrong issue when you submitted.