Unimplemented path in dead member elimination pass (spec constants)

[godlikepanos]

Hi,

I'm hitting an assertion when using -Os in spirv-opt:

spirv-opt: /xxx/source/opt/eliminate_dead_members_pass.cpp:298: spvtools::opt::EliminateDeadMembersPass::RemoveDeadMembers()::<lambda(spvtools::opt::Instruction*)>: Assertion `false && "Not yet implemented."' failed.

The shader is quite simple. It was compiled with glslang without opts:

#version 450 core

layout(constant_id = 0) const int c_0 = 1;
layout(local_size_x = 1, local_size_y = 1, local_size_z = 1) in;

layout(set = 0, binding = 2, std140) buffer ss0_
{
	float u_s[c_0];
};

void main()
{
	u_s[gl_LocalInvocationID.x] = gl_LocalInvocationID.y + c_0;
}

SPIRV for it:

               OpCapability Shader
          %1 = OpExtInstImport "GLSL.std.450"
               OpMemoryModel Logical GLSL450
               OpEntryPoint GLCompute %main "main" %gl_LocalInvocationID
               OpExecutionMode %main LocalSize 1 1 1
               OpSource GLSL 450
               OpName %main "main"
               OpName %c_0 "c_0"
               OpName %ss0_ "ss0_"
               OpMemberName %ss0_ 0 "u_s"
               OpName %_ ""
               OpName %gl_LocalInvocationID "gl_LocalInvocationID"
               OpName %c_0 "c"
               OpDecorate %c_0 SpecId 0
               OpDecorate %_arr_float_c_0 ArrayStride 16
               OpMemberDecorate %ss0_ 0 Offset 0
               OpDecorate %ss0_ BufferBlock
               OpDecorate %_ DescriptorSet 0
               OpDecorate %_ Binding 2
               OpDecorate %gl_LocalInvocationID BuiltIn LocalInvocationId
               OpDecorate %gl_WorkGroupSize BuiltIn WorkgroupSize
       %void = OpTypeVoid
          %3 = OpTypeFunction %void
      %float = OpTypeFloat 32
        %int = OpTypeInt 32 1
        %c_0 = OpSpecConstant %int 1
%_arr_float_c_0 = OpTypeArray %float %c_0
       %ss0_ = OpTypeStruct %_arr_float_c_0
%_ptr_Uniform_ss0_ = OpTypePointer Uniform %ss0_
          %_ = OpVariable %_ptr_Uniform_ss0_ Uniform
      %int_0 = OpConstant %int 0
       %uint = OpTypeInt 32 0
     %v3uint = OpTypeVector %uint 3
%_ptr_Input_v3uint = OpTypePointer Input %v3uint
%gl_LocalInvocationID = OpVariable %_ptr_Input_v3uint Input
     %uint_0 = OpConstant %uint 0
%_ptr_Input_uint = OpTypePointer Input %uint
     %uint_1 = OpConstant %uint 1
         %25 = OpSpecConstantOp %uint IAdd %c_0 %uint_0
%_ptr_Uniform_float = OpTypePointer Uniform %float
%gl_WorkGroupSize = OpConstantComposite %v3uint %uint_1 %uint_1 %uint_1
       %main = OpFunction %void None %3
          %5 = OpLabel
         %20 = OpAccessChain %_ptr_Input_uint %gl_LocalInvocationID %uint_0
         %21 = OpLoad %uint %20
         %23 = OpAccessChain %_ptr_Input_uint %gl_LocalInvocationID %uint_1
         %24 = OpLoad %uint %23
         %26 = OpIAdd %uint %24 %25
         %27 = OpConvertUToF %float %26
         %29 = OpAccessChain %_ptr_Uniform_float %_ %int_0 %21
               OpStore %29 %27
               OpReturn
               OpFunctionEnd

Any plans on implementing this (@s-perron ?)? I'm afraid specialization constants have many issues in the optimizer (Another issue is #3282).

[s-perron]

That assert might have only been in there for me to check if it was used in the cases that I had, and was suppose to be removed. The type of spec constants should be marked as fully used when searching for the live member, so nothing needs to be done for spec constants.

I'll put up a PR that removes the assert, and does a little testing. @godlikepanos Could you just comment out the failing assert and see if that works for you?

[s-perron]

Now that I have looked at it closer I see what the problem was. This is for SpecConstantOp for operations that might extract a particular member. Those member must continue to exist. This will be fixed by adding an extra safety check in find live members. Specifics will be in the PR.