gfx-unit-test/link-time-constant.slang fails with precompiled SPIR-V modules

[cheneym2]

Originally seen in gfx-unit-test-tool/linkTimeConstantD3D12.internal with precompiled target.

Repro:
slang-test gfx-unit-test-tool/linkTimeConstantD3D12

Module 1:

extern static const bool turnOnFeature;
extern static const float constValue;
extern static const uint numthread = 0;
extern static const int arraySize = -1;

// Main entry-point. Write some value into buffer depending on link
// time constant.
[shader("compute")]
[numthreads(numthread, 1, 1)]
void computeMain(
    uint3 sv_dispatchThreadID: SV_DispatchThreadID,
    uniform RWStructuredBuffer<float> buffer)
{
    int array[arraySize];

    array[sv_dispatchThreadID.x] = sv_dispatchThreadID.x;
    if (turnOnFeature)
    {
        buffer[array[0]] = constValue;
    }
    else
    {
        buffer[0] = -1.0;
    }
}

Module 2:

export static const bool turnOnFeature = true;
export static const float constValue = 2.0;
export static const uint numthread = 2;
export static const int arraySize = 4;

[cheneym2]

Looks like the link time constants like

extern static const bool turnOnFeature;
extern static const float constValue;

Are causing compilation failures because they're unresolved by the module that's being compiled.

>	slang.dll!Slang::diagnoseUnresolvedSymbols(Slang::TargetRequest * req, Slang::DiagnosticSink * sink, Slang::IRModule * module) Line 1730	C++
 	slang.dll!Slang::linkIR(Slang::CodeGenContext * codeGenContext) Line 2262	C++
 	slang.dll!Slang::linkAndOptimizeIR(Slang::CodeGenContext * codeGenContext, const Slang::LinkingAndOptimizationOptions & options, Slang::LinkedIR & outLinkedIR) Line 644	C++
 	slang.dll!Slang::emitSPIRVForEntryPointsDirectly(Slang::CodeGenContext * codeGenContext, Slang::ComPtr<Slang::IArtifact> & outArtifact) Line 2080	C++
 	slang.dll!Slang::CodeGenContext::_emitEntryPoints(Slang::ComPtr<Slang::IArtifact> & outArtifact) Line 1816	C++
 	slang.dll!Slang::CodeGenContext::emitPrecompiledDownstreamIR(Slang::ComPtr<Slang::IArtifact> & outArtifact) Line 800	C++
 	slang.dll!Slang::Module::precompileForTarget(SlangCompileTarget target, ISlangBlob * * outDiagnostics) Line 170	C++

static void diagnoseUnresolvedSymbols(TargetRequest* req, DiagnosticSink* sink, IRModule* module)
{
    for (auto globalSym : module->getGlobalInsts())
    {
        if (globalSym->findDecoration<IRImportDecoration>())
        {
            for (;;)
            {
                if (auto constant = as<IRGlobalConstant>(globalSym))
                {
                    if (constant->getOperandCount() == 0)
-->                        sink->diagnose(
                            globalSym->sourceLoc,
                            Diagnostics::unresolvedSymbol,
                            globalSym);
                }

[cheneym2]

Here's a directed test to show the issue:

Test name: tests/library/precompiled-spirv-global.slang

//TEST:COMPILE: tests/library/precompiled-spirv-global.slang -o tests/library/precompiled-spirv-global.slang-module -target spirv -embed-downstream-ir

//import "export-library-global.slang";  //This would make the test pass (it defined myGLobalVar = 42)

extern int myGlobalVar; //This makes the test fail

layout(location = 0) out float4 fragColor;

[shader("fragment")]
void main() {
    fragColor = float4(myGlobalVar);
}

[cheneym2]

Precompiling the module to SPIRV fails when the globals referenced are included only via "extern" declarations and the definitions are not included via directly importing the definition. If "myGlobalVar" is actually defined by importing a module that defines it, there's no problem, as the definition is included.

I think we can support this usecase though by leaving the mGlobalVar declaration in the precompiled SPIRV with import Linkage. But it will only work if the module actually defining myGlobalVar also receives complementary export Linkage.

[cheneym2]

I've posted a directed test for this here: #6532

To run:

build/Release/bin/slang-test.exe tests/library/precompiled-spirv-global

The test crashes as-is, and so it's on the "expected failure list". Any fix for this bug should remove "tests/library/precompiled-spirv-global" from tests/expected-failure-github.txt