Ability to access default values for parameters in a constant buffer

[GregSlazinski]

In HLSL I can do this:

cbuffer XX 
{
   float x;
   float2 param[2]={float2(0,1), float2(2,3)};
}

But when converting to Spir-V the default value information is lost.

Feature Request:
Please make this work for SPIR-V too, because now I have to compile the shader 2 times, non-Spir-V to get default values and Spir-V to generate GLSL code.
Thank you

Also posted here:
KhronosGroup/SPIRV-Headers#125
KhronosGroup/SPIRV-Cross#1094

[tristanlabelle]

HLSL should warn/error on this because the initializers are ignored. You shouldn't see their values anywhere in the generated DXIL code, or SPIR-V code. I filed this bug on the issue: #2384. If you are able to observe the initializer values being taken into account anywhere, that would be bug-worthy. Otherwise, I think there is nothing for SPIR-V to do here, just a missing warning we need to add to the common semantic validation.

[ehsannas]

Yup! Thanks @MrTrillian

[GregSlazinski]

@MrTrillian are you saying default values are always ignored in DXC?
No matter if compiling to dx byte code or spirv?
However this functionality was present in FXC, and it was very useful for me.
Also the default value API is available in both dx11 and dx12 reflection api.
See
https://docs.microsoft.com/en-au/windows/win32/api/d3d11shader/ns-d3d11shader-_d3d11_shader_variable_desc
And
https://docs.microsoft.com/en-us/windows/win32/api/d3d12shader/ns-d3d12shader-_d3d12_shader_variable_desc
So if this functionality is missing, can you please reopen this issue as a feature request to add it?

Please see this example code :
I have a bunch of constants defined in hlsl

BUFFER(Blend)
   const Vec2 BlendOfs4[4]=
   {
      Vec2( 0.5f, -1.5f),
      Vec2(-1.5f, -0.5f),
      Vec2( 1.5f,  0.5f),
      Vec2(-0.5f,  1.5f),
   };
 /*const Vec2 BlendOfs5[5]=
   {
      Vec2(-0.5f, -1.5f),
      Vec2(-1.5f, -0.5f),
      Vec2( 1.5f, -0.5f),
      Vec2(-0.5f,  1.5f),
      Vec2( 1.5f,  1.5f),
   };*/
   const Vec2 BlendOfs6[6]=
   {
      Vec2( 0.5f, -2.5f),

      Vec2(-0.5f, -0.5f),
      Vec2( 1.5f, -0.5f),

      Vec2(-2.5f,  0.5f),

      Vec2(-0.5f,  1.5f),
      Vec2( 1.5f,  1.5f),
   };
   const Vec2 BlendOfs8[8]=
   {
      Vec2(-1.5f, -2.5f),

      Vec2( 0.5f, -1.5f),
      Vec2( 2.5f, -1.5f),

      Vec2(-1.5f, -0.5f),

      Vec2( 1.5f,  0.5f),

      Vec2(-2.5f,  1.5f),
      Vec2(-0.5f,  1.5f),

      Vec2( 1.5f,  2.5f),
   };
 /*const Vec2 BlendOfs9[9]=
   {
      Vec2(-2.5f, -2.5f),
      Vec2(-0.5f, -2.5f),
      Vec2( 1.5f, -2.5f),
      Vec2(-2.5f, -0.5f),
      Vec2(-0.5f, -0.5f),
      Vec2( 1.5f, -0.5f),
      Vec2(-2.5f,  1.5f),
      Vec2(-0.5f,  1.5f),
      Vec2( 1.5f,  1.5f),
   };*/
   const Vec2 BlendOfs12[12]=
   {
      Vec2( 0.5f, -3.5f),

      Vec2(-1.5f, -2.5f),

      Vec2( 0.5f, -1.5f),
      Vec2( 2.5f, -1.5f),

      Vec2(-3.5f, -0.5f),
      Vec2(-1.5f, -0.5f),

      Vec2( 1.5f,  0.5f),
      Vec2( 3.5f,  0.5f),

      Vec2(-2.5f,  1.5f),
      Vec2(-0.5f,  1.5f),

      Vec2( 1.5f,  2.5f),

      Vec2(-0.5f,  3.5f),
   };
 /*const Vec2 BlendOfs13[13]=
   {
      Vec2(-0.5f, -3.5f),
      Vec2( 1.5f, -2.5f),
      Vec2(-0.5f, -1.5f),
      Vec2(-3.5f, -0.5f),
      Vec2(-1.5f, -0.5f),
      Vec2( 1.5f, -0.5f),
      Vec2( 3.5f, -0.5f),
      Vec2(-2.5f,  1.5f),
      Vec2(-0.5f,  1.5f),
      Vec2( 1.5f,  1.5f),
      Vec2( 3.5f,  1.5f),
      Vec2(-0.5f,  3.5f),
      Vec2( 1.5f,  3.5f),
   };*/
BUFFER_END

It's extremely useful to be able to define default values in hlsl so I can just extract them from reflection api.
If I had to store the values on the cpu side then it's easy to make mistake if for example I decide to change array size length on the hlsl but forget to change it on cpu as well. This way I have defined everything in one place so risk of introducing bugs is smaller.