Add test for dot2add

[llvm-beanz]

Add a test to Test/Feature/HLSLLib that exercises the dot2add function:

float dot2add( half2 a, half2 b, float acc );

See https://learn.microsoft.com/en-us/windows/win32/direct3dhlsl/hlsl-shader-model-6-4-features-for-direct3d-12#single-precision-floating-point-2-element-dot-product-and-accumulate for details.

---

Generic HLSL function test guidelines follow.

In Test\Feature\HLSLLib create, if applicable: (reference the HLSL headers for the types supported by the intrinsic)

• Test for 16 bit int types (< intrinsic >.int16.test)
• Test for Half type (< intrinsic >.fp16.test)
• Test for 32 bit types (< intrinsic >.32.test)
• Test for 64 bit int types (< intrinsic >.int64.test)
• Test for Double type (< intrinsic >.fp64.test)

A .test file should contain

• a source portion; If multiple .test files can use the same source; it can go in its own file and be referenced in the run portion of each .test file instead.

@@ -0,0 +1,54 @@
#--- source.hlsl

StructuredBuffer<float4> In : register(t0);
RWStructuredBuffer<float> Out : register(u1);

[numthreads(1,1,1)]
void main() {
// A single test can test for all scalar/vector length as shown here.
  Out[0] = length(In[0]); // Test float4
  Out[1] = length(In[1].x); // Test float
  Out[2] = length(In[1].yzw); // Test float3
  Out[3] = length(In[1].yz); // Test float2
}

• a yaml portion; If multiple .test files can use the same YAML, it can go in its own file and be referenced in the run portion of each .test file instead.

//--- pipeline.yaml

---
Shaders:
  - Stage: Compute
    Entry: main
    DispatchSize: [1, 1, 1]
Buffers:
  - Name: In
    Format: Float32
    Stride: 16
    Data: [ 4, 4, 4, 4, 3.14159, 0, 5, 12 ]
  - Name: Out
    Format: Float32
    Stride: 4
    ZeroInitSize: 12
  - Name: ExpectedOut # The result we expect
    Format: Float32
    Stride: 4
    Data: [ 8, 3.14159, 13, 5 ]
Results:  # A test might have more than 1 result.
  - Result: Test1
    Rule: BufferFuzzy # there is also a BufferExact rule
    ULPT: 1
    Actual: Out
    Expected: ExpectedOut
DescriptorSets:
  - Resources:
    - Name: In
      Kind: StructuredBuffer
      DirectXBinding:
        Register: 0
        Space: 0
      VulkanBinding:
        Binding: 0
    - Name: Out
      Kind: RWStructuredBuffer
      DirectXBinding:
        Register: 1
        Space: 0
      VulkanBinding:
        Binding: 1
...
#--- end

• A run portion; which will be unique to each .test file.

# UNSUPPORTED: Clang-Vulkan
# RUN: split-file %s %t
# RUN: %dxc_target -T cs_6_5 -Fo %t.o %t/source.hlsl
# RUN: %offloader %t/pipeline.yaml %t.o 

Currently all tests should include # UNSUPPORTED: Clang-Vulkan.
Tests for 16 bit floating point should have a # REQUIRES: Half.
Tests for 16 bit integer should have a # REQUIRES: Int16.
Tests for 64 bit floating point should have a # REQUIRES: Double.
Tests for 64 bit integer should have a # REQUIRES: Int64.