[SPIR-V] Fatal error instead of ordinary error with file and line number when SV_IsFrontFace is not bool.

[neversleeping]

Description
When entry point parameter with SV_IsFrontFace semantic have type other than bool, SPIR-V compilation result in fatal error:

fatal error: generated SPIR-V is invalid: [VUID-FrontFacing-FrontFacing-04231] According to the Vulkan spec BuiltIn FrontFacing variable needs to be a bool scalar. ID <2> (OpVariable) is not a bool scalar.
  %gl_FrontFacing = OpVariable %_ptr_Input_uint Input

note: please file a bug report on https://github.com/Microsoft/DirectXShaderCompiler/issues with source code if possible

Steps to Reproduce
https://godbolt.org/z/1v7ec17nG

Compile with -E PSMain -T ps_6_6 -spirv

struct VSOut
{
	float3 pos : SV_Position;
};

float4 PSMain(
    VSOut input,
    uint isFrontFace : SV_IsFrontFace) : SV_Target
{
	return (isFrontFace ? 1.0 : -1.0);
}

Actual Behavior
Ordinary error with file and line number should be displayed instead of fatal error.

Environment

• DXC version: 1.8 - 1.8.0.4666 (release-1.8.2407, 8df0a9d)
• Host Operating System: Windows 11 23H2

[damyanp]

Note that we don't generally do validation for semantics in the frontend and instead rely on the DXIL & SPIR-V validators to do this.

@s-perron - I don't know if you want to do something different for SPIR-V.

[s-perron]

Because of the poor error message from spirv-val, we try to catch these earlier when possible. We could try to validate the type somewhere in SpirvEmitter.cpp. However, these type of bugs are low priority for us at this time.

We will accept a fix, but my team will not be looking into it.