Implement the `GetRenderTargetSamplePosition` HLSL Function

[farzonl]

• Implement GetRenderTargetSamplePosition clang builtin,
• Link GetRenderTargetSamplePosition clang builtin with hlsl_intrinsics.h
• Add sema checks for GetRenderTargetSamplePosition to CheckHLSLBuiltinFunctionCall in SemaChecking.cpp
• Add codegen for GetRenderTargetSamplePosition to EmitHLSLBuiltinExpr in CGBuiltin.cpp
• Add codegen tests to clang/test/CodeGenHLSL/builtins/GetRenderTargetSamplePosition.hlsl
• Add sema tests to clang/test/SemaHLSL/BuiltIns/GetRenderTargetSamplePosition-errors.hlsl
• Create the int_dx_GetRenderTargetSamplePosition intrinsic in IntrinsicsDirectX.td
• Create the DXILOpMapping of int_dx_GetRenderTargetSamplePosition to 76 in DXIL.td
• Create the GetRenderTargetSamplePosition.ll and GetRenderTargetSamplePosition_errors.ll tests in llvm/test/CodeGen/DirectX/

DirectX

DXIL Opcode	DXIL OpName	Shader Model	Shader Stages
76	RenderTargetGetSamplePosition	6.0	('pixel',)

SPIR-V

There is no support for GetRenderTargetSamplePosition when targeting SPIR-V.

Test Case(s)

Example 1

//dxc GetRenderTargetSamplePosition_test.hlsl -T lib_6_8 -enable-16bit-types -O0

[numthreads(1, 1, 1)]
[shader("pixel")]
float2 fn( ) : SV_Target {
	int p1;
	return GetRenderTargetSamplePosition(p1);
}

HLSL:

Gets the sampling position (x,y) for a given sample index.

float<2> GetRenderTargetSamplePosition( in int<1> Index
);

Parameters

Item	Description
Index	[in] A zero-based sample index.

Return Value

The (x,y) position of the given sample.

Remarks

Use this function and GetRenderTargetSampleCount to find out the number and position of the sampling locations for a render target.

Minimum Shader Model

This function is supported in the following shader models.

Shader Model	Supported
Shader Model 4 and higher shader models	yes
Shader Model 3 (DirectX HLSL)	no
Shader Model 2 (DirectX HLSL)	no
Shader Model 1 (DirectX HLSL)	no

See also

Intrinsic Functions (DirectX HLSL)

[davidcook-msft]

@farzonl to create a new issue to track making this Op in SPIR-V