[SPIRV] Add shadow function when only global variable declared in the module

llvm/lib/Target/SPIRV/SPIRVAsmPrinter.cpp

@@ -85,9 +85,12 @@ class SPIRVAsmPrinter : public AsmPrinter {
   void outputModuleSections();
   void outputFPFastMathDefaultInfo();
   bool isHidden() {
-    return MF->getFunction()
-        .getFnAttribute(SPIRV_BACKEND_SERVICE_FUN_NAME)
-        .isValid();
+    const Function &F = MF->getFunction();
+    if (F.getFnAttribute(SPIRV_BACKEND_SERVICE_FUN_NAME).isValid())
+      return true;
+    if (F.getName() == "__spirv_globals_entry")
+      return true;
+    return false;
   }
 
   void emitInstruction(const MachineInstr *MI) override;
@@ -278,6 +281,10 @@ void SPIRVAsmPrinter::outputInstruction(const MachineInstr *MI) {
 }
 
 void SPIRVAsmPrinter::emitInstruction(const MachineInstr *MI) {
+  const Function &F = MF->getFunction();
+  if (F.getName() == "__spirv_globals_entry") {
+    return;
+  }
   SPIRV_MC::verifyInstructionPredicates(MI->getOpcode(),
                                         getSubtargetInfo().getFeatureBits());
 
@@ -295,8 +302,14 @@ void SPIRVAsmPrinter::emitInstruction(const MachineInstr *MI) {
 }
 
 void SPIRVAsmPrinter::outputModuleSection(SPIRV::ModuleSectionType MSType) {
-  for (const MachineInstr *MI : MAI->getMSInstrs(MSType))
-    outputInstruction(MI);
+  const Function &F = MF->getFunction();
+  for (const MachineInstr *MI : MAI->getMSInstrs(MSType)) {
+    if (F.getName() != "__spirv_globals_entry" || ((MI->getOpcode() != SPIRV::OpName) 
+                                    && (MI->getOpcode() != SPIRV::OpTypeVoid)
+                                    && (MI->getOpcode() != SPIRV::OpTypeFunction))) { 
+      outputInstruction(MI);
+    }
+  }
 }
 
 void SPIRVAsmPrinter::outputDebugSourceAndStrings(const Module &M) {

llvm/lib/Target/SPIRV/SPIRVEmitIntrinsics.cpp

@@ -3020,6 +3020,36 @@ bool SPIRVEmitIntrinsics::runOnModule(Module &M) {
   parseFunDeclarations(M);
   insertConstantsForFPFastMathDefault(M);
 
+  // If there are no functions but there is at least one global variable,
+  // create a shadow function to "anchor" global handling in codegen.
+  bool HasAnyFunction = false;
+  for (auto &F : M)
+    if (!F.isDeclaration() && !F.isIntrinsic())
+      HasAnyFunction = true;
+
+  Function *ShadowFunc = nullptr;
+  if (!HasAnyFunction) {
+      for (auto GI = M.global_begin(), GE = M.global_end(); GI != GE; ) {
+          GlobalVariable *GV = &*GI++;
+          if (GV->hasInternalLinkage()) {
+              GV->eraseFromParent();
+              Changed = true;
+          } else if (ShadowFunc == nullptr) {
+              LLVMContext &Ctx = M.getContext();
+              auto *FTy = FunctionType::get(Type::getVoidTy(Ctx), /*isVarArg=*/false);
+              ShadowFunc = Function::Create(
+                  FTy, GlobalValue::InternalLinkage, "__spirv_globals_entry", &M);
+
+              // Create a basic block and insert a ret void
+              BasicBlock *BB = BasicBlock::Create(Ctx, "entry", ShadowFunc);
+              IRBuilder<> B(BB);
+              B.CreateRetVoid();
+
+              Changed = true;
+          }
+      }
+  }
+
   TodoType.clear();
   for (auto &F : M)
     Changed |= runOnFunction(F);