[Debug info] Only the first four elements of a matrix loaded from a buffer get debug values

Version: dxcompiler.dll 1.9(5402-0d3ee6b5)(1.9.0.5402) - 1.9.0.5402 (0d3ee6b55-dirty)

Repro files: matrix_buffer_load.zip

dxc -T cs_6_0 -Zi -Qembed_debug -Od -Fc float4x4.ll float4x4.hlsl

RWStructuredBuffer<float4x4> buffer : register(u0);

[numthreads(1, 1, 1)]
void main()
{
    float4x4 value  = buffer[0];
    float4x4 result = value * 2;
    buffer[1] = result;
}

Actual

All 16 elements of value are live SSA values, but only the four produced by the first bufferLoad get a dbg.value:

  %1  = call %dx.types.ResRet.f32 @dx.op.bufferLoad.f32(i32 68, %dx.types.Handle %buffer_UAV_structbuf, i32 0, i32 0)
  %2  = extractvalue %dx.types.ResRet.f32 %1, 0
  %3  = extractvalue %dx.types.ResRet.f32 %1, 1
  %4  = extractvalue %dx.types.ResRet.f32 %1, 2
  %5  = extractvalue %dx.types.ResRet.f32 %1, 3
  %6  = call %dx.types.ResRet.f32 @dx.op.bufferLoad.f32(i32 68, %dx.types.Handle %buffer_UAV_structbuf, i32 0, i32 16)
  %7  = extractvalue %dx.types.ResRet.f32 %6, 0
  ...
  %20 = extractvalue %dx.types.ResRet.f32 %16, 3

  ; nothing for %7..%10, %12..%15, %17..%20
  call void @llvm.dbg.value(metadata float %2, ...)  ; var:"value" !DIExpression(DW_OP_bit_piece,  0, 32)
  call void @llvm.dbg.value(metadata float %3, ...)  ; var:"value" !DIExpression(DW_OP_bit_piece, 32, 32)
  call void @llvm.dbg.value(metadata float %4, ...)  ; var:"value" !DIExpression(DW_OP_bit_piece, 64, 32)
  call void @llvm.dbg.value(metadata float %5, ...)  ; var:"value" !DIExpression(DW_OP_bit_piece, 96, 32)

result on the other hand is computed rather than loaded, gets all 16 fragments.

float2x2 is unaffected because it has exactly four elements.

Expected

value should get one dbg.value per element, like result does.

Unpack matrix_buffer_load.zip and begin with the float4x4.hlsl reproduction using the reported dxc command, then inspect float4x4.ll. Compare the dbg.value fragments emitted for the loaded value with those for the computed result across the listed matrix cases. Done means every matrix element receives a dbg.value entry, including the unaffected float2x2 baseline.