[SPIRV] Implement type deduction and reference to function declarations for indirect calls using SPV_INTEL_function_pointers (#111159)

This PR improves implementation of SPV_INTEL_function_pointers and type
inference for phi-nodes and indirect calls.

Author: VyacheslavLevytskyy

llvm/lib/Target/SPIRV/SPIRVAsmPrinter.cpp

@@ -78,6 +78,11 @@ class SPIRVAsmPrinter : public AsmPrinter {
   void outputExecutionMode(const Module &M);
   void outputAnnotations(const Module &M);
   void outputModuleSections();
+  bool isHidden() {
+    return MF->getFunction()
+        .getFnAttribute(SPIRV_BACKEND_SERVICE_FUN_NAME)
+        .isValid();
+  }
 
   void emitInstruction(const MachineInstr *MI) override;
   void emitFunctionEntryLabel() override {}
@@ -131,7 +136,7 @@ void SPIRVAsmPrinter::emitFunctionHeader() {
   TII = ST->getInstrInfo();
   const Function &F = MF->getFunction();
 
-  if (isVerbose()) {
+  if (isVerbose() && !isHidden()) {
     OutStreamer->getCommentOS()
         << "-- Begin function "
         << GlobalValue::dropLLVMManglingEscape(F.getName()) << '\n';
@@ -149,11 +154,18 @@ void SPIRVAsmPrinter::outputOpFunctionEnd() {
 
 // Emit OpFunctionEnd at the end of MF and clear BBNumToRegMap.
 void SPIRVAsmPrinter::emitFunctionBodyEnd() {
+  // Do not emit anything if it's an internal service function.
+  if (isHidden())
+    return;
   outputOpFunctionEnd();
   MAI->BBNumToRegMap.clear();
 }
 
 void SPIRVAsmPrinter::emitOpLabel(const MachineBasicBlock &MBB) {
+  // Do not emit anything if it's an internal service function.
+  if (isHidden())
+    return;
+
   MCInst LabelInst;
   LabelInst.setOpcode(SPIRV::OpLabel);
   LabelInst.addOperand(MCOperand::createReg(MAI->getOrCreateMBBRegister(MBB)));
@@ -162,7 +174,9 @@ void SPIRVAsmPrinter::emitOpLabel(const MachineBasicBlock &MBB) {
 }
 
 void SPIRVAsmPrinter::emitBasicBlockStart(const MachineBasicBlock &MBB) {
-  assert(!MBB.empty() && "MBB is empty!");
+  // Do not emit anything if it's an internal service function.
+  if (MBB.empty())
+    return;
 
   // If it's the first MBB in MF, it has OpFunction and OpFunctionParameter, so
   // OpLabel should be output after them.

llvm/lib/Target/SPIRV/SPIRVCallLowering.cpp

@@ -36,6 +36,13 @@ bool SPIRVCallLowering::lowerReturn(MachineIRBuilder &MIRBuilder,
                                     const Value *Val, ArrayRef<Register> VRegs,
                                     FunctionLoweringInfo &FLI,
                                     Register SwiftErrorVReg) const {
+  // Ignore if called from the internal service function
+  if (MIRBuilder.getMF()
+          .getFunction()
+          .getFnAttribute(SPIRV_BACKEND_SERVICE_FUN_NAME)
+          .isValid())
+    return true;
+
   // Maybe run postponed production of types for function pointers
   if (IndirectCalls.size() > 0) {
     produceIndirectPtrTypes(MIRBuilder);
@@ -280,6 +287,10 @@ bool SPIRVCallLowering::lowerFormalArguments(MachineIRBuilder &MIRBuilder,
                                              const Function &F,
                                              ArrayRef<ArrayRef<Register>> VRegs,
                                              FunctionLoweringInfo &FLI) const {
+  // Discard the internal service function
+  if (F.getFnAttribute(SPIRV_BACKEND_SERVICE_FUN_NAME).isValid())
+    return true;
+
   assert(GR && "Must initialize the SPIRV type registry before lowering args.");
   GR->setCurrentFunc(MIRBuilder.getMF());
 
@@ -576,6 +587,16 @@ bool SPIRVCallLowering::lowerCall(MachineIRBuilder &MIRBuilder,
     lowerFormalArguments(FirstBlockBuilder, *CF, VRegArgs, FuncInfo);
   }
 
+  // Ignore the call if it's called from the internal service function
+  if (MIRBuilder.getMF()
+          .getFunction()
+          .getFnAttribute(SPIRV_BACKEND_SERVICE_FUN_NAME)
+          .isValid()) {
+    // insert a no-op
+    MIRBuilder.buildTrap();
+    return true;
+  }
+
   unsigned CallOp;
   if (Info.CB->isIndirectCall()) {
     if (!ST->canUseExtension(SPIRV::Extension::SPV_INTEL_function_pointers))