Incorrect GLSL conversion when indexing into a structure.

[jbsheblak]

I'm having an issue with a conversion from an HLSL blob to GLSL v440 when indexing into a structure.

This is the original source:

struct STestStruct
{
   float4 value0;
};

cbuffer psBuffer
{   
   STestStruct             uc_values[4];
   uint                    uc_idx;
};

struct PS_INPUT
{
   float4 position : SV_POSITION;
};

struct PS_OUTPUT
{
   float4 color : SV_TARGET0;
};

PS_OUTPUT main(PS_INPUT input)
{
   PS_OUTPUT output;   
   output.color = uc_values[uc_idx].value0;   
   return output;
}

This is the HLSL blob generated by FXC:

//
// Generated by Microsoft (R) HLSL Shader Compiler 9.29.952.3111
//
//
//   fxc /T ps_4_1 D:/shaders/conversion_tests/test.fs.hlsl
//
//
// Buffer Definitions:
//
// cbuffer psBuffer
// {
//
//   struct
//   {
//
//       float4 value0;                 // Offset:    0
//
//   } uc_values[4];                    // Offset:    0 Size:    64
//   uint uc_idx;                       // Offset:   64 Size:     4
//
// }
//
//
// Resource Bindings:
//
// Name                                 Type  Format         Dim Slot Elements
// ------------------------------ ---------- ------- ----------- ---- --------
// psBuffer                          cbuffer      NA          NA    0        1
//
//
//
// Input signature:
//
// Name                 Index   Mask Register SysValue Format   Used
// -------------------- ----- ------ -------- -------- ------ ------
// SV_POSITION              0   xyzw        0      POS  float
//
//
// Output signature:
//
// Name                 Index   Mask Register SysValue Format   Used
// -------------------- ----- ------ -------- -------- ------ ------
// SV_TARGET                0   xyzw        0   TARGET  float   xyzw
//
ps_4_1
dcl_globalFlags refactoringAllowed
dcl_constantbuffer cb0[5], dynamicIndexed
dcl_output o0.xyzw
dcl_temps 1
mov r0.x, cb0[4].x
mov o0.xyzw, cb0[r0.x + 0].xyzw
ret
// Approximately 3 instruction slots used

and this is the GLSL that is generated:

#version 440
#extension GL_ARB_separate_shader_objects : enable

struct uc_values_Type {
        vec4 value0;
};
layout(binding = 0, std140) uniform psBuffer {
        uc_values_Type uc_values[4];
        uint uc_idx;
};
layout(location = 0) out vec4 SV_TARGET0;
uint u_xlatu0;
void main()
{
    //MOV
    u_xlatu0 = uc_idx;
    //MOV
    SV_TARGET0 = uc_values[0].value0[int(u_xlatu0)];
    //RET
    return;
}

The issue is on the line with the assignment to SV_TARGET0. 'uc_idx' should be used to index into the 'uc_values' array, but instead is indexing the first member of the structure in that array.

I believe the correct translation should be:

SV_TARGET0 = uc_values[int(u_xlatu0)].value0;

I'm not very familiar with the code, but after stepping through my test case, it seems like this involves ShaderInfo::GetShaderVarIndexedFullName not taking into account Operand::m_suboperands. When decoding the shader, the operand has a fixed immediate value of 0 from the 'r0.x + 0' expression but also a relative value from the 'r0.x' portion. This could all be wrong though, as I'm not very familiar with the code. :)

The blob was generated with: "fxc.exe" /T ps_4_1 test.fs.hlsl"
HLSLcc was run with LANG_440 set and the following flags:
HLSLCC_FLAG_UNIFORM_BUFFER_OBJECT | HLSLCC_FLAG_INOUT_SEMANTIC_NAMES | HLSLCC_FLAG_COMBINE_TEXTURE_SAMPLERS | HLSLCC_FLAG_NVN_TARGET

Let me know if I can provide any additional information!

[shadowndacorner]

I'm having this issue as well when indexing into a UBO. It's easy enough to fix by hand, but that kind of defeats the purpose.
`
struct LightData
{
float4 l_Position;
float4 l_Direction;
float4 l_Color;
float4 l_Params;
};

cbuffer LightBuffer
{
LightData g_Light[64];
};

...

for(int i = 0; i < min(NumLights, 64); ++i)
{
float3 lightDir = g_Light[i].l_Direction;
...`

The loop compiles into
u_xlat4.xyz = g_Light[0].l_Direction[u_xlati17].xyz;
where it should compile into
u_xlat4.xyz = g_Light[u_xlati17].l_Direction.xyz;

The shader was compiled under LANG_430 with only HLSLCC_FLAG_UNIFORM_BUFFER_OBJECT enabled.