[WIP] Fix CoopMat.MapElement crashing the compiler

[Copilot]

This work updates the IR type legalization handling for CoopMat.MapElement to rebuild the intrinsic when its operands or result type are legalized, and it adds a regression test for the minimal repro.

Changes Made

• Update legalizeCoopMatMapElementIFunc to re-emit the instruction when operands/types are legalized and to drop invalid this arguments.
• Add tests/bugs/coopmat-map-element-crash.slang regression test (self-contained repro).

Testing

• ./build/Debug/bin/slang-test tests/bugs/coopmat-map-element-crash.slang (currently fails with “replaced inst still has use” and needs follow-up).

Original prompt

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This section details on the original issue you should resolve

<issue_title>CoopMat.MapElement crashes the compiler</issue_title>
<issue_description>```
// Minimal repro for CoopMat.MapElement crash.
// Keep this file self-contained: no external includes required.

struct ReproParams
{
half* output; // output buffer
int outputW;
};

[numthreads(256, 1, 1)]
void coopmat_map_element_repro(
ConstantBuffer params,
uint3 groupThreadId : SV_GroupThreadID,
uint3 groupId : SV_GroupID)
{
static const int TILE_M = 64;
static const int TILE_N = 32;
// Fill accumulator with a constant to exercise MapElement.
linalg::CoopMat<float, MemoryScope.Workgroup, TILE_M, TILE_N, linalg::CoopMatMatrixUse.MatrixAccumulator> matC;
matC.fill(1.0f);

// Direct write via MapElement.
matC = matC.MapElement((uint row, uint col, float acc) => {
    int outIdx = col * params.outputW;
    params.output[outIdx] = half(acc);
    return acc;
});

}

Crashes in 

slang-compiler.dll!Slang::handleSignal(Slang::SignalType type, const char * message) Line 115 C++

slang-compiler.dll!Slang::IRTypeLegalizationPass::processModule(Slang::IRModule * module) Line 3669 C++
slang-compiler.dll!Slang::legalizeTypes(Slang::IRTypeLegalizationContext * context) Line 3780 C++
slang-compiler.dll!Slang::legalizeResourceTypes(Slang::IRModule * module, Slang::TargetProgram * target, Slang::DiagnosticSink * sink) Line 3926 C++
slang-compiler.dll!Slang::linkAndOptimizeIR'::159'::<lambda_87>::operator()<Slang::IRModule,Slang::TargetProgram * &,Slang::DiagnosticSink * &>(Slang::IRModule * m, Slang::TargetProgram * & <a_0>, Slang::DiagnosticSink * & <a_1>) Line 1361 C++
slang-compiler.dll!Slang::wrapPass<Slang::linkAndOptimizeIR'::159'::<lambda_87>,Slang::TargetProgram * &,Slang::DiagnosticSink * &>(Slang::CodeGenContext * codeGenContext, const char * passName, Slang::linkAndOptimizeIR::__l159::<lambda_87> && passFunc, Slang::IRModule * irModule, Slang::TargetProgram * & <args_0>, Slang::DiagnosticSink * & <args_1>) Line 60 C++
slang-compiler.dll!Slang::linkAndOptimizeIR(Slang::CodeGenContext * codeGenContext, const Slang::LinkingAndOptimizationOptions & options, Slang::LinkedIR & outLinkedIR) Line 1361 C++
slang-compiler.dll!Slang::emitSPIRVForEntryPointsDirectly(Slang::CodeGenContext * codeGenContext, Slang::ComPtrSlang::IArtifact & outArtifact) Line 2767 C++
slang-compiler.dll!Slang::CodeGenContext::_emitEntryPoints(Slang::ComPtrSlang::IArtifact & outArtifact) Line 1145 C++
slang-compiler.dll!Slang::CodeGenContext::emitEntryPoints(Slang::ComPtrSlang::IArtifact & outArtifact) Line 1234 C++
slang-compiler.dll!Slang::TargetProgram::_createWholeProgramResult(Slang::DiagnosticSink * sink, Slang::EndToEndCompileRequest * endToEndReq) Line 40 C++
slang-compiler.dll!Slang::EndToEndCompileRequest::generateOutput(Slang::TargetProgram * targetProgram) Line 474 C++
slang-compiler.dll!Slang::EndToEndCompileRequest::generateOutput(Slang::ComponentType * program) Line 725 C++
slang-compiler.dll!Slang::EndToEndCompileRequest::generateOutput() Line 732 C++
slang-compiler.dll!Slang::EndToEndCompileRequest::executeActionsInner() Line 267 C++
slang-compiler.dll!Slang::EndToEndCompileRequest::executeActions() Line 277 C++
slang-compiler.dll!Slang::EndToEndCompileRequest::compile() Line 1473 C++
slang-compiler.dll!spCompile(slang::ICompileRequest * request) Line 757 C++

## Comments on the Issue (you are @copilot in this section)

<comments>
</comments>

• Fixes CoopMat.MapElement crashes the compiler #9629

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[csyonghe]

@copilot continue.

[csyonghe]

Closing this, a diagnostic has been added to report this as an unsupported case.