Fix crash in Spirv -lower-host-to-llvm pass

[mehdi_amini]

Summary

When providing with a spirv module as input where no conversion happens
the code didn't defend against broken invariant.

We'll fail the pass here, but it's not clear if it is the right thing
or if the module should just be ignored.

Fixes #59971

[kuhar]

LGTM

[antiagainst]

Nice, thanks Mehdi!

mlir/lib/Conversion/SPIRVToLLVM/ConvertLaunchFuncToLLVMCalls.cpp

 /// Encodes the SPIR-V module's symbolic name into the name of the entry point
 /// function.
 static LogicalResult encodeKernelName(spirv::ModuleOp module) {
   StringRef spvModuleName = *module.getSymName();
   // We already know that the module contains exactly one entry point function
   // based on `getKernelGlobalVariables()` call. Update this function's name
   // to:
   //   {spv_module_name}_{function_name}
-  auto entryPoint = *module.getOps<spirv::EntryPointOp>().begin();
+  auto entryPoints = module.getOps<spirv::EntryPointOp>();
+  if (!llvm::hasSingleElement(entryPoints)) {
+    return module.emitError(
+        "The module must contain exactly one entry point function");
+  }
+  spirv::EntryPointOp entryPoint = *entryPoints.begin();
   StringRef funcName = entryPoint.getFn();
   auto funcOp = module.lookupSymbol<spirv::FuncOp>(entryPoint.getFnAttr());
   StringAttr newFuncName =
       StringAttr::get(module->getContext(), spvModuleName + "_" + funcName);
   if (failed(SymbolTable::replaceAllSymbolUses(funcOp, newFuncName, module)))
     return failure();
   SymbolTable::setSymbolName(funcOp, newFuncName);
   return success();
void runOnOperation() override {
 
     ConversionTarget target(*context);
     target.addLegalDialect<LLVM::LLVMDialect>();
     if (failed(applyPartialConversion(module, target, std::move(patterns))))
       signalPassFailure();
 
     // Finally, modify the kernel function in SPIR-V modules to avoid symbolic
     // conflicts.
-    for (auto spvModule : module.getOps<spirv::ModuleOp>())
-      (void)encodeKernelName(spvModule);
+    for (auto spvModule : module.getOps<spirv::ModuleOp>()) {
+      if (failed(encodeKernelName(spvModule))) {
+        signalPassFailure();
+        return;
+      }
+    }
   }
 };
 } // namespace
 
 std::unique_ptr<mlir::OperationPass<mlir::ModuleOp>>
 mlir::createLowerHostCodeToLLVMPass() {
   return std::make_unique<LowerHostCodeToLLVM>();
 }

mlir/test/Conversion/SPIRVToLLVM/lower-host-to-llvm-calls_fail.mlir

+// RUN: mlir-opt --lower-host-to-llvm %s -verify-diagnostics
+
+module {
+// expected-error @+1 {{The module must contain exactly one entry point function}}
+  spirv.module Logical GLSL450 {
+  }
+}