Re: [PATCH v7 0/6] MR491: Draft: vkd3d-shader/dxil: Handle control flow instructions.

[Giovanni Mascellani (＠giomasce)]

I just noticed that in some cases FXC generates PHI nodes which mention the same origin block more than once. For example,
```hlsl
struct PSInput
{
    float4 color : COLOR;
};

float4 main(PSInput input) : SV_TARGET
{
    float y = 0;
    switch (input.color.x)
    {
    	case 0:
        	y = 100;
            break;
    	case 1:
        	y = 101;
            break;
    	case 2:
            break;
    	case 3:
            break;
    	case 4:
        	y = 104;
            break;
    	case 5:
        	y = 105;
            break;
        default:
            y = 200;
            break;
    }

input.color.y = y;

return input.color;
}
```
compiles to
```
define void @main() {
  %1 = call float @dx.op.loadInput.f32(i32 4, i32 0, i32 0, i8 0, i32 undef)  ; LoadInput(inputSigId,rowIndex,colIndex,gsVertexAxis)
  %2 = call float @dx.op.loadInput.f32(i32 4, i32 0, i32 0, i8 2, i32 undef)  ; LoadInput(inputSigId,rowIndex,colIndex,gsVertexAxis)
  %3 = call float @dx.op.loadInput.f32(i32 4, i32 0, i32 0, i8 3, i32 undef)  ; LoadInput(inputSigId,rowIndex,colIndex,gsVertexAxis)
  %4 = fptosi float %1 to i32
  switch i32 %4, label %9 [
    i32 0, label %5
    i32 1, label %6
    i32 2, label %10
    i32 3, label %10
    i32 4, label %7
    i32 5, label %8
  ]

; <label>:5                                       ; preds = %0
  br label %10

; <label>:6                                       ; preds = %0
  br label %10

; <label>:7                                       ; preds = %0
  br label %10

; <label>:8                                       ; preds = %0
  br label %10

; <label>:9                                       ; preds = %0
  br label %10

; <label>:10                                      ; preds = %9, %8, %7, %6, %5, %0, %0
  %11 = phi float [ 2.000000e+02, %9 ], [ 1.050000e+02, %8 ], [ 1.040000e+02, %7 ], [ 0.000000e+00, %0 ], [ 0.000000e+00, %0 ], [ 1.010000e+02, %6 ], [ 1.000000e+02, %5 ]
  call void @dx.op.storeOutput.f32(i32 5, i32 0, i32 0, i8 0, float %1)  ; StoreOutput(outputSigId,rowIndex,colIndex,value)
  call void @dx.op.storeOutput.f32(i32 5, i32 0, i32 0, i8 1, float %11)  ; StoreOutput(outputSigId,rowIndex,colIndex,value)
  call void @dx.op.storeOutput.f32(i32 5, i32 0, i32 0, i8 2, float %2)  ; StoreOutput(outputSigId,rowIndex,colIndex,value)
  call void @dx.op.storeOutput.f32(i32 5, i32 0, i32 0, i8 3, float %3)  ; StoreOutput(outputSigId,rowIndex,colIndex,value)
  ret void
}
```

As you can see, `%0` is duplicated both in the preds list and in the PHI node. This feels quite broken and it's understandably forbidden by SPIR-V. Could you please add my (or a similar) source code to a shader runner test and implement a deduplication logic, emitting an error if values of duplicated PHI entries do not match?