Direct3D Shader Internal Compiler Error X8000: Invalid Bytecode

Question

When compiling this simple pixel shader:

Texture2D tex0 : register(t0);
Texture2D tex1 : register(t1);

SamplerState s : register(s0);

float4 main(float2 tc : TEXCOORD0) : SV_TARGET
{
    Texture2D tex = tex0;
    if (tc.x > 0.5)
    {
        tex = tex1;
    }
    return tex.SampleLevel(s, tc, 0);
}

Using the command line fxc.exe /T ps_4_0 hello.hlsl I get:

Microsoft (R) Direct3D Shader Compiler 10.1 (using C:\Windows Kits\10\bin\10.0.17763.0\x86\D3DCOMPILER_47.dll)
Copyright (C) 2013 Microsoft. All rights reserved.

error X8000: D3D11 Internal Compiler Error: Invalid Bytecode: Invalid operand type for operand #3 of opcode #8 (counts are 1-based).
error X8000: D3D11 Internal Compiler Error: Invalid Bytecode: Can't continue validation - aborting.

What am I doing wrong?

Answer 1

The internal compiler error is not a helpful error here, but the pattern you used above is just not something most people write. The same shader works if you write it as:

Texture2D tex0 : register(t0);
Texture2D tex1 : register(t1);

SamplerState s : register(s0);

float4 main(float2 tc : TEXCOORD0) : SV_TARGET
{
    if (tc.x > 0.5)
    {
        return tex1.SampleLevel(s, tc, 0);
    }
    else
    {
        return tex0.SampleLevel(s, tc, 0);
    }
}

Note that the DXIL compiler for Shader Model 6 returns a more sensible error in this case:

error: local resource not guaranteed to map to unique global resource. Use /Zi for source location.