[SPIR-V] Atomic counter emitted when combining RWStructuredBuffer and RayQuery

[MarijnS95]

A very simple shader using RWStructuredBuffer or RayQuery seems to compile fine and no counter binding is emitted unless {Increment,Decrement}Counter is used. However, combine them in an unrelated way like below:

RWStructuredBuffer<uint> test : register(u0, space0);

[numthreads(1, 1, 1)]
void main(uint3 DTid: SV_DispatchThreadID) {
    test[0] = 1;
    RayQuery<RAY_FLAG_ACCEPT_FIRST_HIT_AND_END_SEARCH |
             RAY_FLAG_FORCE_OPAQUE> q;
}

Compiled with: dxc -E main -T cs_6_5 structuredbuffer_counter.hlsl -spirv -fspv-target-env=vulkan1.2 this results in:

; SPIR-V
; Version: 1.5
; Generator: Google spiregg; 0
; Bound: 29
; Schema: 0
               OpCapability Shader
               OpCapability RayQueryKHR
               OpExtension "SPV_KHR_ray_query"
               OpMemoryModel Logical GLSL450
               OpEntryPoint GLCompute %main "main" %test %counter_var_test %gl_GlobalInvocationID
               OpExecutionMode %main LocalSize 1 1 1
               OpSource HLSL 650
               OpName %type_RWStructuredBuffer_uint "type.RWStructuredBuffer.uint"
               OpName %test "test"
               OpName %type_ACSBuffer_counter "type.ACSBuffer.counter"
               OpMemberName %type_ACSBuffer_counter 0 "counter"
               OpName %counter_var_test "counter.var.test"
               OpName %main "main"
               OpName %param_var_DTid "param.var.DTid"
               OpName %rayQueryKHR "rayQueryKHR"
               OpDecorate %gl_GlobalInvocationID BuiltIn GlobalInvocationId
               OpDecorate %test DescriptorSet 0
               OpDecorate %test Binding 0
               OpDecorate %counter_var_test DescriptorSet 0
               OpDecorate %counter_var_test Binding 1
               OpDecorate %_runtimearr_uint ArrayStride 4
               OpMemberDecorate %type_RWStructuredBuffer_uint 0 Offset 0
               OpDecorate %type_RWStructuredBuffer_uint Block
               OpMemberDecorate %type_ACSBuffer_counter 0 Offset 0
               OpDecorate %type_ACSBuffer_counter Block
       %uint = OpTypeInt 32 0
     %uint_1 = OpConstant %uint 1
        %int = OpTypeInt 32 1
      %int_0 = OpConstant %int 0
     %uint_0 = OpConstant %uint 0
%_runtimearr_uint = OpTypeRuntimeArray %uint
%type_RWStructuredBuffer_uint = OpTypeStruct %_runtimearr_uint
%_ptr_StorageBuffer_type_RWStructuredBuffer_uint = OpTypePointer StorageBuffer %type_RWStructuredBuffer_uint
%type_ACSBuffer_counter = OpTypeStruct %int
%_ptr_StorageBuffer_type_ACSBuffer_counter = OpTypePointer StorageBuffer %type_ACSBuffer_counter
     %v3uint = OpTypeVector %uint 3
%_ptr_Input_v3uint = OpTypePointer Input %v3uint
       %void = OpTypeVoid
         %20 = OpTypeFunction %void
%_ptr_Function_v3uint = OpTypePointer Function %v3uint
         %22 = OpTypeFunction %void %_ptr_Function_v3uint
%rayQueryKHR = OpTypeRayQueryKHR
%_ptr_Function_rayQueryKHR = OpTypePointer Function %rayQueryKHR
%_ptr_StorageBuffer_uint = OpTypePointer StorageBuffer %uint
       %test = OpVariable %_ptr_StorageBuffer_type_RWStructuredBuffer_uint StorageBuffer
%counter_var_test = OpVariable %_ptr_StorageBuffer_type_ACSBuffer_counter StorageBuffer
%gl_GlobalInvocationID = OpVariable %_ptr_Input_v3uint Input
       %main = OpFunction %void None %20
         %25 = OpLabel
         %26 = OpVariable %_ptr_Function_rayQueryKHR Function
%param_var_DTid = OpVariable %_ptr_Function_v3uint Function
         %27 = OpLoad %v3uint %gl_GlobalInvocationID
         %28 = OpAccessChain %_ptr_StorageBuffer_uint %test %int_0 %uint_0
               OpStore %28 %uint_1
               OpReturn
               OpFunctionEnd

In particular:

               OpName %counter_var_test "counter.var.test"
[...]
%type_ACSBuffer_counter = OpTypeStruct %int
%_ptr_StorageBuffer_type_ACSBuffer_counter = OpTypePointer StorageBuffer %type_ACSBuffer_counter
     %v3uint = OpTypeVector %uint 3
[...]
               OpDecorate %counter_var_test DescriptorSet 0
               OpDecorate %counter_var_test Binding 1
[...]
%counter_var_test = OpVariable %_ptr_StorageBuffer_type_ACSBuffer_counter StorageBuffer

The counter_var_test variable/binding should not be there, any idea why it shows up?

When compiling for DXIL the Dim stays at r/w unless {Increment,Decrement}Counter is added, then it turns into r/w+cnt as expected.

[ehsannas]

Thanks for reporting this @MarijnS95 . I have traced this to be a bug in SPIRV-Tools (spirv-opt should be optimizing that counter away, but it's not doing it).

[MarijnS95]

Awesome @ehsannas, simple fix for a simple issue, the resulting SPIR-V is clean again now 👍

At what pace are submodule hashes generally updated?

[ehsannas]

Usually once a month, but since this is an important fix for raytracing/query to work, we will pull it in soon.