comp.cxx

struct buffer_t {
  ivec4 data;
};

[[using spirv: buffer, binding(0)]]
buffer_t buffer;

[[spirv::comp(1)]]
void comp_main() { 
  for(int i = 0; i < buffer.data.x; ++i) {
    if(buffer.data.y < buffer.data.z) { }
  }
}

int main() {
  @spirv(comp_main);
}

shader.spvasm

               OpCapability Shader
               OpExtension "GL_EXT_scalar_block_layout"
               OpMemoryModel Logical GLSL450
               OpEntryPoint GLCompute %_Z9comp_mainv "_Z9comp_mainv" %buffer
               OpExecutionMode %_Z9comp_mainv LocalSize 1 1 1
               OpName %buffer_t "buffer_t"
               OpMemberName %buffer_t 0 "data"
               OpName %buffer "buffer"
               OpName %_Z9comp_mainv "_Z9comp_mainv"
               OpDecorate %buffer_t Block
               OpMemberDecorate %buffer_t 0 Offset 0
               OpDecorate %buffer Binding 0
               OpDecorate %buffer DescriptorSet 0
       %uint = OpTypeInt 32 0
     %v4uint = OpTypeVector %uint 4
   %buffer_t = OpTypeStruct %v4uint
%_ptr_StorageBuffer_buffer_t = OpTypePointer StorageBuffer %buffer_t
     %buffer = OpVariable %_ptr_StorageBuffer_buffer_t StorageBuffer
       %void = OpTypeVoid
          %8 = OpTypeFunction %void
%_ptr_Function_uint = OpTypePointer Function %uint
     %uint_0 = OpConstant %uint 0
%_ptr_StorageBuffer_v4uint = OpTypePointer StorageBuffer %v4uint
%_ptr_StorageBuffer_uint = OpTypePointer StorageBuffer %uint
       %bool = OpTypeBool
     %uint_1 = OpConstant %uint 1

%_Z9comp_mainv = OpFunction %void None %8
          %9 = OpLabel
         %11 = OpVariable %_ptr_Function_uint Function
               OpStore %11 %uint_0
               OpBranch %13

               ; Loop header
         %13 = OpLabel
         %14 = OpLoad %uint %11
         %16 = OpAccessChain %_ptr_StorageBuffer_v4uint %buffer %uint_0
         %18 = OpAccessChain %_ptr_StorageBuffer_uint %16 %uint_0
         %19 = OpLoad %uint %18
         %21 = OpSLessThan %bool %14 %19
               OpLoopMerge %22 %23 None
               OpBranchConditional %21 %24 %22

               ; if-statement
         %24 = OpLabel
         %25 = OpAccessChain %_ptr_StorageBuffer_v4uint %buffer %uint_0
         %27 = OpAccessChain %_ptr_StorageBuffer_uint %25 %uint_1
         %28 = OpLoad %uint %27
         %29 = OpLoad %uint %11
         %30 = OpSLessThan %bool %28 %29

               ; This shader fails to validate when the merge block is %23, 
               ; even though it dominates both branch targets %31 and %32.
               ; It passes when the merge block is %32, even though that 
               ; does not dominate both branch targets.

               ; OpSelectionMerge %32 None 

               OpSelectionMerge %23 None
               OpBranchConditional %30 %31 %32

         %31 = OpLabel
               OpBranch %23
         %32 = OpLabel
               OpBranch %23

         %23 = OpLabel
         %33 = OpLoad %uint %11
         %34 = OpIAdd %uint %33 %uint_1
               OpStore %11 %34
               OpBranch %13

         %22 = OpLabel
               OpReturn

               OpFunctionEnd

spirv-val

error: line 40: Header block 25[%25] is contained in the loop construct headed by 17[%17], but its merge block 24[%24] is not
  %25 = OpLabel