pVectorExtractDynamic with spec constant index is not correct

[tksuoran]

I am running into #1178 when targeting metal:

• half4 foo; foo[specialization constant] ends up foo[0] in metal shader.
• Putting specialization constant first into a temp variable works around the issue, but only if optimizations are not used.
• A silly switch case successfully works around the issue even when optimizations are used.

I will try to fill in more details later.

[HansKristian-Work]

I cannot reproduce this, so I need reproducing SPIR-V.

; SPIR-V
; Version: 1.0
; Generator: Khronos Glslang Reference Front End; 11
; Bound: 37
; Schema: 0
               OpCapability Shader
          %1 = OpExtInstImport "GLSL.std.450"
               OpMemoryModel Logical GLSL450
               OpEntryPoint GLCompute %main "main" %gl_GlobalInvocationID
               OpExecutionMode %main LocalSize 64 1 1
               OpSource GLSL 450
               OpName %main "main"
               OpName %v "v"
               OpName %SSBO "SSBO"
               OpMemberName %SSBO 0 "init_value"
               OpMemberName %SSBO 1 "ovalues"
               OpName %_ ""
               OpName %gl_GlobalInvocationID "gl_GlobalInvocationID"
               OpName %IDX "IDX"
               OpDecorate %_runtimearr_float ArrayStride 4
               OpDecorate %SSBO BufferBlock
               OpMemberDecorate %SSBO 0 Offset 0
               OpMemberDecorate %SSBO 1 Offset 16
               OpDecorate %_ Binding 0
               OpDecorate %_ DescriptorSet 0
               OpDecorate %gl_GlobalInvocationID BuiltIn GlobalInvocationId
               OpDecorate %IDX SpecId 0
               OpDecorate %gl_WorkGroupSize BuiltIn WorkgroupSize
       %void = OpTypeVoid
          %3 = OpTypeFunction %void
      %float = OpTypeFloat 32
    %v4float = OpTypeVector %float 4
%_ptr_Function_v4float = OpTypePointer Function %v4float
%_runtimearr_float = OpTypeRuntimeArray %float
       %SSBO = OpTypeStruct %v4float %_runtimearr_float
%_ptr_Uniform_SSBO = OpTypePointer Uniform %SSBO
          %_ = OpVariable %_ptr_Uniform_SSBO Uniform
        %int = OpTypeInt 32 1
      %int_0 = OpConstant %int 0
%_ptr_Uniform_v4float = OpTypePointer Uniform %v4float
      %int_1 = OpConstant %int 1
       %uint = OpTypeInt 32 0
     %v3uint = OpTypeVector %uint 3
%_ptr_Input_v3uint = OpTypePointer Input %v3uint
%gl_GlobalInvocationID = OpVariable %_ptr_Input_v3uint Input
     %uint_0 = OpConstant %uint 0
%_ptr_Input_uint = OpTypePointer Input %uint
        %IDX = OpSpecConstant %int 0
%_ptr_Function_float = OpTypePointer Function %float
%_ptr_Uniform_float = OpTypePointer Uniform %float
    %uint_64 = OpConstant %uint 64
     %uint_1 = OpConstant %uint 1
%gl_WorkGroupSize = OpConstantComposite %v3uint %uint_64 %uint_1 %uint_1
       %main = OpFunction %void None %3
          %5 = OpLabel
          %v = OpVariable %_ptr_Function_v4float Function
         %17 = OpAccessChain %_ptr_Uniform_v4float %_ %int_0
         %18 = OpLoad %v4float %17
               OpStore %v %18
         %26 = OpAccessChain %_ptr_Input_uint %gl_GlobalInvocationID %uint_0
         %27 = OpLoad %uint %26

                 %loaded = OpLoad %v4float %v
                 %31 = OpVectorExtractDynamic %float %loaded %IDX

         %33 = OpAccessChain %_ptr_Uniform_float %_ %int_1 %27
               OpStore %33 %31
               OpReturn
               OpFunctionEnd

#include <metal_stdlib>
#include <simd/simd.h>

using namespace metal;

struct SSBO
{
    float4 init_value;
    float ovalues[1];
};

constant int IDX_tmp [[function_constant(0)]];
constant int IDX = is_function_constant_defined(IDX_tmp) ? IDX_tmp : 0;
constant uint3 gl_WorkGroupSize [[maybe_unused]] = uint3(64u, 1u, 1u);

kernel void main0(device SSBO& _6 [[buffer(0)]], uint3 gl_GlobalInvocationID [[thread_position_in_grid]])
{
    float4 v = _6.init_value;
    _6.ovalues[gl_GlobalInvocationID.x] = v[IDX];
}