[SPIR-V] Add descriptor heap stride specialization constant attribute

[jzakharovnv]

Building off of #8519, this PR adds [[vk::resource_heap_stride_constant_id(id)]] and [[vk::sampler_heap_stride_constant_id(id)]] attributes that emit the descriptor heap ArrayStride as a SPIR-V specialization constant using ArrayStrideIdEXT, allowing applications to override the stride at pipeline creation time via VkSpecializationInfo without recompiling the shader. It is part 4/4 in a series.

The attribute initializer supplies the default stride value and must be a power of two in [8, 256]. The CLI flags -fvk-resource-heap-stride and -fvk-sampler-heap-stride take higher precedence and suppress these attributes with a warning when both are specified.

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[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.

[jzakharovnv]

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[Tobski]

I've reviewed this as best I can, everything looks fine code wise to me in terms of using the heap extension. My only feedback is the same as I gave offline - that we really need the descriptor heap stride to be calculated via OpConstantSizeOf by default - but I know that's in hand. Noting it here in case any other readers come across it 😊

[Guang-035]

; SPIR-V
; Version: 1.6
; Generator: Google spiregg; 0
; Bound: 99
; Schema: 0
               OpCapability DescriptorHeapEXT
               OpCapability Shader
               OpExtension "SPV_EXT_descriptor_heap"
               OpExtension "SPV_KHR_untyped_pointers"
               OpMemoryModel Logical GLSL450
               OpEntryPoint GLCompute %main "main" %gl_GlobalInvocationID %outputBytes %resource_heap
               OpExecutionMode %main LocalSize 1 1 1
               OpSource HLSL 660
               OpName %type_RWByteAddressBuffer "type.RWByteAddressBuffer"
               OpName %outputBytes "outputBytes"
               OpName %type_untyped_pointer "type.untyped.pointer"
               OpName %resource_heap "resource_heap"
               OpName %main "main"
               OpName %type_buffer_ext "type.buffer.ext"
               OpName %type_StructuredBuffer_uint "type.StructuredBuffer.uint"
               OpName %type_RWStructuredBuffer_uint "type.RWStructuredBuffer.uint"
               OpName %type_ByteAddressBuffer "type.ByteAddressBuffer"
               OpName %type_buffer_ext_0 "type.buffer.ext"
               OpName %type_ConstantBuffer_Constants "type.ConstantBuffer.Constants"
               OpMemberName %type_ConstantBuffer_Constants 0 "value"
               OpDecorate %gl_GlobalInvocationID BuiltIn GlobalInvocationId
               OpDecorate %resource_heap BuiltIn ResourceHeapEXT
               OpDecorate %outputBytes DescriptorSet 0
               OpDecorate %outputBytes Binding 0
               OpDecorate %_runtimearr_uint ArrayStride 4
               OpMemberDecorate %type_RWByteAddressBuffer 0 Offset 0
               OpDecorate %type_RWByteAddressBuffer Block
               OpDecorate %_runtimearr_type_buffer_ext ArrayStride 64
               OpMemberDecorate %type_StructuredBuffer_uint 0 Offset 0
               OpMemberDecorate %type_StructuredBuffer_uint 0 NonWritable
               OpDecorate %type_StructuredBuffer_uint Block
               OpMemberDecorate %type_RWStructuredBuffer_uint 0 Offset 0
               OpDecorate %type_RWStructuredBuffer_uint Block
               OpMemberDecorate %type_ByteAddressBuffer 0 Offset 0
               OpMemberDecorate %type_ByteAddressBuffer 0 NonWritable
               OpDecorate %type_ByteAddressBuffer Block
               OpDecorate %_runtimearr_type_buffer_ext_0 ArrayStride 64
               OpMemberDecorate %type_ConstantBuffer_Constants 0 Offset 0
               OpDecorate %type_ConstantBuffer_Constants Block
       %uint = OpTypeInt 32 0
     %uint_0 = OpConstant %uint 0
     %uint_1 = OpConstant %uint 1
     %uint_2 = OpConstant %uint 2
     %uint_3 = OpConstant %uint 3
        %int = OpTypeInt 32 1
      %int_0 = OpConstant %int 0
     %uint_4 = OpConstant %uint 4
%_runtimearr_uint = OpTypeRuntimeArray %uint
%type_RWByteAddressBuffer = OpTypeStruct %_runtimearr_uint
%_ptr_StorageBuffer_type_RWByteAddressBuffer = OpTypePointer StorageBuffer %type_RWByteAddressBuffer
     %v3uint = OpTypeVector %uint 3
%_ptr_Input_v3uint = OpTypePointer Input %v3uint
%type_untyped_pointer = OpTypeUntypedPointerKHR UniformConstant
       %void = OpTypeVoid
         %28 = OpTypeFunction %void
%type_buffer_ext = OpTypeBufferEXT StorageBuffer
%_runtimearr_type_buffer_ext = OpTypeRuntimeArray %type_buffer_ext
%type_StructuredBuffer_uint = OpTypeStruct %_runtimearr_uint
%_ptr_StorageBuffer_type_StructuredBuffer_uint = OpTypePointer StorageBuffer %type_StructuredBuffer_uint
%type_RWStructuredBuffer_uint = OpTypeStruct %_runtimearr_uint
%_ptr_StorageBuffer_type_RWStructuredBuffer_uint = OpTypePointer StorageBuffer %type_RWStructuredBuffer_uint
%type_ByteAddressBuffer = OpTypeStruct %_runtimearr_uint
%_ptr_StorageBuffer_type_ByteAddressBuffer = OpTypePointer StorageBuffer %type_ByteAddressBuffer
%type_buffer_ext_0 = OpTypeBufferEXT Uniform
%_runtimearr_type_buffer_ext_0 = OpTypeRuntimeArray %type_buffer_ext_0
%type_ConstantBuffer_Constants = OpTypeStruct %uint
%_ptr_Uniform_type_ConstantBuffer_Constants = OpTypePointer Uniform %type_ConstantBuffer_Constants
%_ptr_StorageBuffer_uint = OpTypePointer StorageBuffer %uint
%_ptr_Uniform_uint = OpTypePointer Uniform %uint
%outputBytes = OpVariable %_ptr_StorageBuffer_type_RWByteAddressBuffer StorageBuffer
%gl_GlobalInvocationID = OpVariable %_ptr_Input_v3uint Input
%resource_heap = OpUntypedVariableKHR %type_untyped_pointer UniformConstant
%_ptr_Input_uint = OpTypePointer Input %uint
       %main = OpFunction %void None %28
         %36 = OpLabel
         %37 = OpUntypedAccessChainKHR %type_untyped_pointer %_runtimearr_type_buffer_ext %resource_heap %uint_0
         %38 = OpBufferPointerEXT %_ptr_StorageBuffer_type_StructuredBuffer_uint %37
         %39 = OpUntypedAccessChainKHR %type_untyped_pointer %_runtimearr_type_buffer_ext %resource_heap %uint_1
         %40 = OpBufferPointerEXT %_ptr_StorageBuffer_type_RWStructuredBuffer_uint %39
         %41 = OpUntypedAccessChainKHR %type_untyped_pointer %_runtimearr_type_buffer_ext %resource_heap %uint_2
         %42 = OpBufferPointerEXT %_ptr_StorageBuffer_type_ByteAddressBuffer %41
         %43 = OpUntypedAccessChainKHR %type_untyped_pointer %_runtimearr_type_buffer_ext_0 %resource_heap %uint_3
         %44 = OpBufferPointerEXT %_ptr_Uniform_type_ConstantBuffer_Constants %43
         %45 = OpUntypedAccessChainKHR %type_untyped_pointer %_runtimearr_type_buffer_ext %resource_heap %uint_0
         %46 = OpBufferPointerEXT %_ptr_StorageBuffer_type_StructuredBuffer_uint %45
         %47 = OpAccessChain %_ptr_Input_uint %gl_GlobalInvocationID %int_0
         %48 = OpLoad %uint %47
         %49 = OpBitcast %int %48
         %50 = OpAccessChain %_ptr_StorageBuffer_uint %46 %int_0 %49
         %51 = OpLoad %uint %50
         %52 = OpUntypedAccessChainKHR %type_untyped_pointer %_runtimearr_type_buffer_ext %resource_heap %uint_2
         %53 = OpBufferPointerEXT %_ptr_StorageBuffer_type_ByteAddressBuffer %52
         %54 = OpAccessChain %_ptr_Input_uint %gl_GlobalInvocationID %int_0
         %55 = OpLoad %uint %54
         %56 = OpIMul %uint %55 %uint_4
         %57 = OpShiftRightLogical %uint %56 %uint_2
         %58 = OpAccessChain %_ptr_StorageBuffer_uint %53 %uint_0 %57
         %59 = OpLoad %uint %58
         %60 = OpIAdd %uint %51 %59
         %61 = OpUntypedAccessChainKHR %type_untyped_pointer %_runtimearr_type_buffer_ext_0 %resource_heap %uint_3
         %62 = OpBufferPointerEXT %_ptr_Uniform_type_ConstantBuffer_Constants %61
         %63 = OpAccessChain %_ptr_Uniform_uint %62 %int_0
         %64 = OpLoad %uint %63
         %65 = OpIAdd %uint %60 %64
         %66 = OpAccessChain %_ptr_Input_uint %gl_GlobalInvocationID %int_0
         %67 = OpLoad %uint %66
         %68 = OpUntypedAccessChainKHR %type_untyped_pointer %_runtimearr_type_buffer_ext %resource_heap %uint_1
         %69 = OpBufferPointerEXT %_ptr_StorageBuffer_type_RWStructuredBuffer_uint %68
         %70 = OpAccessChain %_ptr_StorageBuffer_uint %69 %int_0 %67
               OpStore %70 %65
         %71 = OpAccessChain %_ptr_Input_uint %gl_GlobalInvocationID %int_0
         %72 = OpLoad %uint %71
         %73 = OpIMul %uint %72 %uint_4
         %74 = OpShiftRightLogical %uint %73 %uint_2
         %75 = OpAccessChain %_ptr_Input_uint %gl_GlobalInvocationID %int_0
         %76 = OpLoad %uint %75
         %77 = OpUntypedAccessChainKHR %type_untyped_pointer %_runtimearr_type_buffer_ext %resource_heap %uint_1
         %78 = OpBufferPointerEXT %_ptr_StorageBuffer_type_RWStructuredBuffer_uint %77
         %79 = OpAccessChain %_ptr_StorageBuffer_uint %78 %int_0 %76
         %80 = OpLoad %uint %79
         %81 = OpAccessChain %_ptr_StorageBuffer_uint %outputBytes %uint_0 %74
               OpStore %81 %80
         %82 = OpUntypedAccessChainKHR %type_untyped_pointer %_runtimearr_type_buffer_ext %resource_heap %uint_4
         %83 = OpBufferPointerEXT %_ptr_StorageBuffer_type_StructuredBuffer_uint %82
         %84 = OpUntypedAccessChainKHR %type_untyped_pointer %_runtimearr_type_buffer_ext %resource_heap %uint_4
         %85 = OpBufferPointerEXT %_ptr_StorageBuffer_type_StructuredBuffer_uint %84
         %86 = OpAccessChain %_ptr_Input_uint %gl_GlobalInvocationID %int_0
         %87 = OpLoad %uint %86
         %88 = OpIMul %uint %87 %uint_4
         %89 = OpIAdd %uint %88 %uint_4
         %90 = OpShiftRightLogical %uint %89 %uint_2
         %91 = OpUntypedAccessChainKHR %type_untyped_pointer %_runtimearr_type_buffer_ext %resource_heap %uint_4
         %92 = OpBufferPointerEXT %_ptr_StorageBuffer_type_StructuredBuffer_uint %91
         %93 = OpAccessChain %_ptr_Input_uint %gl_GlobalInvocationID %int_0
         %94 = OpLoad %uint %93
         %95 = OpBitcast %int %94
         %96 = OpAccessChain %_ptr_StorageBuffer_uint %92 %int_0 %95
         %97 = OpLoad %uint %96
         %98 = OpAccessChain %_ptr_StorageBuffer_uint %outputBytes %uint_0 %90
               OpStore %98 %97
               OpReturn
               OpFunctionEnd

Thanks for the great PR. The overall implementation looks good and this is a very helpful addition. I really appreciate the work you put into supporting this feature.
I left a couple of questions/comments about the generated SPIR-V output, mainly around duplicated descriptor-heap access sequences and the ArrayStride vs ArrayStrideIdEXT decoration. Could you take a look when you have a chance?

Q1:
The generated SPIR-V appears to contain many unused IDs and duplicated resource-heap access sequences. For example, %37/%38, %45/%46, %52/%53, %68/%69, %77/%78, %84/%85, and %91/%92 all recreate buffer pointers from the descriptor heap, even when they refer to the same heap index and resource type. Is this expected or acceptable behavior in DXC?

[Guang-035]

Q2:
Per to the previous Tobski's comment, Another issue is that the descriptor-heap runtime arrays are currently decorated with a literal ArrayStride 64. For example:

OpDecorate %_runtimearr_type_buffer_ext_0 ArrayStride 64

For OpTypeBufferEXT, should DXC instead emit OpConstantSizeOf to produce a stride ID, and then use OpDecorateId with ArrayStrideIdEXT? For example:

%stride = OpConstantSizeOf %uint %type_buffer_ext_0
OpDecorateId %_runtimearr_type_buffer_ext_0 ArrayStrideIdEXT %stride

This would avoid hardcoding the descriptor-heap buffer stride as 64 and derive it from the OpTypeBufferEXT element size instead. Is the current ArrayStride 64 output expected, or should DXC emit the ArrayStrideIdEXT pattern here?