Custom session causes dispatchCompute failed

[Hyiker]

Hi, I'm a beginner to slang and gfx. I created gfx GPU device with DX12 backend on Windows, everything worked fine with these code pieces initially:

Slang::ComPtr<gfx::IShaderProgram> ProgramManager::createProgram(
    std::string_view filePath,
    std::vector<ProgramEntryPoint> entryPoints) const {

    Slang::ComPtr<slang::ISession> pSlangSession = mpDevice->gfxDevice->getSlangSession();

    Slang::ComPtr<slang::IBlob> diagnosticsBlob;
    slang::IModule* module =
        pSlangSession->loadModule(filePath.data(), diagnosticsBlob.writeRef());
    diagnoseIfNeeded(diagnosticsBlob);
    VL_ASSERT(module != nullptr);

    std::vector<slang::IComponentType*> componentTypes;
    componentTypes.push_back(module);

    for (auto& ep : entryPoints) {
        Slang::ComPtr<slang::IEntryPoint> stageEntryPoint;
        module->findEntryPointByName(ep.first.c_str(),
                                     stageEntryPoint.writeRef());
        componentTypes.push_back(stageEntryPoint);
    }

    Slang::ComPtr<slang::IComponentType> linkedProgram;
    pSlangSession->createCompositeComponentType(
        componentTypes.data(), componentTypes.size(), linkedProgram.writeRef(),
        diagnosticsBlob.writeRef());
    diagnoseIfNeeded(diagnosticsBlob);

    gfx::IShaderProgram::Desc programDesc = {};
    programDesc.slangGlobalScope = linkedProgram;

    return mpDevice->gfxDevice->createProgram(programDesc);
}

and shader:

RWTexture2D<float4> dstTex;

cbuffer CB {
    uint2 frameDim;
}

// CameraData cameraData;

[shader("compute")]
[numthreads(16, 16, 1)]
void main(uint3 threadId: SV_DispatchThreadID) {
    uint2 pixel = threadId.xy;
    if (any(pixel >= frameDim.xy))
        return;

    float2 c = float2(pixel) / frameDim.xy;

    if (pixel.x > 180) {
        dstTex[pixel] = float4(c, 0, 1);
    } else {
        dstTex[pixel] = float4(c, 0, 1);
    }
}

Then I create my own session(for customizing searchpath):

Slang::ComPtr<gfx::IShaderProgram> ProgramManager::createProgram(
    std::string_view filePath,
    std::vector<ProgramEntryPoint> entryPoints) const {
    // Create session
    slang::SessionDesc sessionDesc;

    std::vector<std::string> searchPaths;
    std::vector<const char*> slangSearchPaths;

    for (auto& path : getShaderSearchDirectories()) {
        searchPaths.push_back(path);
        slangSearchPaths.push_back(searchPaths.back().data());
    }
    sessionDesc.searchPaths = slangSearchPaths.data();
    sessionDesc.searchPathCount = (SlangInt)slangSearchPaths.size();

    slang::TargetDesc targetDesc;
    targetDesc.format = getSlangCompileTarget();
    targetDesc.profile = mpDevice->slangGlobalSession->findProfile("sm_6_6");
    targetDesc.forceGLSLScalarBufferLayout = true;
    sessionDesc.targetCount = 1;
    sessionDesc.targets = &targetDesc;
        targetDesc.flags &= ~SLANG_TARGET_FLAG_GENERATE_SPIRV_DIRECTLY;

    Slang::ComPtr<slang::ISession> pSlangSession;
    mpDevice->slangGlobalSession->createSession(sessionDesc,
                                                pSlangSession.writeRef());

    Slang::ComPtr<slang::IBlob> diagnosticsBlob;
    slang::IModule* module =
        pSlangSession->loadModule(filePath.data(), diagnosticsBlob.writeRef());
    diagnoseIfNeeded(diagnosticsBlob);
    VL_ASSERT(module != nullptr);

    std::vector<slang::IComponentType*> componentTypes;
    componentTypes.push_back(module);

    for (auto& ep : entryPoints) {
        Slang::ComPtr<slang::IEntryPoint> stageEntryPoint;
        module->findEntryPointByName(ep.first.c_str(),
                                     stageEntryPoint.writeRef());
        componentTypes.push_back(stageEntryPoint);
    }

    Slang::ComPtr<slang::IComponentType> linkedProgram;
    pSlangSession->createCompositeComponentType(
        componentTypes.data(), componentTypes.size(), linkedProgram.writeRef(),
        diagnosticsBlob.writeRef());
    diagnoseIfNeeded(diagnosticsBlob);

    gfx::IShaderProgram::Desc programDesc = {};
    programDesc.slangGlobalScope = linkedProgram;

    return mpDevice->gfxDevice->createProgram(programDesc);
}

After this modification, dispatchCompute command failed without any debug layer output. And the crash only show up when I tried to access the cbuffer fields in my compute shader. If I move the frameDim outside cbuffer, everything worked fine again. The inconsistent behaviours are quite confusing.

[csyonghe]

The problem may be linked with how you set frameDim in your command buffer encoding/dispatch code. Can you post that part of your application here too so we can take a look?