[NFC] Replace Function handling of attributes with less confusing calls

To avoid magic constants and confusing indexes.

clang/lib/CodeGen/CodeGenModule.cpp

@@ -2118,7 +2118,7 @@ void CodeGenModule::SetFunctionAttributes(GlobalDecl GD, llvm::Function *F,
            F->arg_begin()->getType()
              ->canLosslesslyBitCastTo(F->getReturnType()) &&
            "unexpected this return");
-    F->addAttribute(1, llvm::Attribute::Returned);
+    F->addParamAttr(0, llvm::Attribute::Returned);
   }
 
   // Only a few attributes are set on declarations; these may later be
@@ -2144,15 +2144,13 @@ void CodeGenModule::SetFunctionAttributes(GlobalDecl GD, llvm::Function *F,
     assert(HasBody && "Inline builtin declarations should always have an "
                       "available body!");
     if (shouldEmitFunction(FDBody))
-      F->addAttribute(llvm::AttributeList::FunctionIndex,
-                      llvm::Attribute::NoBuiltin);
+      F->addFnAttr(llvm::Attribute::NoBuiltin);
   }
 
   if (FD->isReplaceableGlobalAllocationFunction()) {
     // A replaceable global allocation function does not act like a builtin by
     // default, only if it is invoked by a new-expression or delete-expression.
-    F->addAttribute(llvm::AttributeList::FunctionIndex,
-                    llvm::Attribute::NoBuiltin);
+    F->addFnAttr(llvm::Attribute::NoBuiltin);
   }
 
   if (isa<CXXConstructorDecl>(FD) || isa<CXXDestructorDecl>(FD))

llvm/include/llvm/IR/Function.h

@@ -251,6 +251,11 @@ public:
   /// Set the attribute list for this Function.
   void setAttributes(AttributeList Attrs) { AttributeSets = Attrs; }
 
+  /// Add return value attributes to this function.
+  void addRetAttr(Attribute::AttrKind Kind) {
+    addAttribute(AttributeList::ReturnIndex, Kind);
+  }
+
   /// Add function attributes to this function.
   void addFnAttr(Attribute::AttrKind Kind) {
     addAttribute(AttributeList::FunctionIndex, Kind);

llvm/lib/IR/Core.cpp

@@ -2502,7 +2502,7 @@ void LLVMAddTargetDependentFunctionAttr(LLVMValueRef Fn, const char *A,
                                         const char *V) {
   Function *Func = unwrap<Function>(Fn);
   Attribute Attr = Attribute::get(Func->getContext(), A, V);
-  Func->addAttribute(AttributeList::FunctionIndex, Attr);
+  Func->addFnAttr(Attr);
 }
 
 /*--.. Operations on parameters ............................................--*/

llvm/lib/Target/AArch64/AArch64ISelLowering.cpp

@@ -17744,7 +17744,7 @@ void AArch64TargetLowering::insertSSPDeclarations(Module &M) const {
         Type::getInt8PtrTy(M.getContext()));
     if (Function *F = dyn_cast<Function>(SecurityCheckCookie.getCallee())) {
       F->setCallingConv(CallingConv::Win64);
-      F->addAttribute(1, Attribute::AttrKind::InReg);
+      F->addParamAttr(0, Attribute::AttrKind::InReg);
     }
     return;
   }

llvm/lib/Target/ARM/ARMISelLowering.cpp

@@ -20371,7 +20371,7 @@ void ARMTargetLowering::insertSSPDeclarations(Module &M) const {
       "__security_check_cookie", Type::getVoidTy(M.getContext()),
       Type::getInt8PtrTy(M.getContext()));
   if (Function *F = dyn_cast<Function>(SecurityCheckCookie.getCallee()))
-    F->addAttribute(1, Attribute::AttrKind::InReg);
+    F->addParamAttr(0, Attribute::AttrKind::InReg);
 }
 
 Value *ARMTargetLowering::getSDagStackGuard(const Module &M) const {

llvm/lib/Target/X86/X86ISelLowering.cpp

@@ -2714,7 +2714,7 @@ void X86TargetLowering::insertSSPDeclarations(Module &M) const {
         Type::getInt8PtrTy(M.getContext()));
     if (Function *F = dyn_cast<Function>(SecurityCheckCookie.getCallee())) {
       F->setCallingConv(CallingConv::X86_FastCall);
-      F->addAttribute(1, Attribute::AttrKind::InReg);
+      F->addParamAttr(0, Attribute::AttrKind::InReg);
     }
     return;
   }

llvm/lib/Transforms/IPO/FunctionAttrs.cpp

@@ -1076,7 +1076,7 @@ static bool addNonNullAttrs(const SCCNodeSet &SCCNodes) {
         // which prevents us from speculating about the entire SCC
         LLVM_DEBUG(dbgs() << "Eagerly marking " << F->getName()
                           << " as nonnull\n");
-        F->addAttribute(AttributeList::ReturnIndex, Attribute::NonNull);
+        F->addRetAttr(Attribute::NonNull);
         ++NumNonNullReturn;
         MadeChange = true;
       }
@@ -1094,7 +1094,7 @@ static bool addNonNullAttrs(const SCCNodeSet &SCCNodes) {
         continue;
 
       LLVM_DEBUG(dbgs() << "SCC marking " << F->getName() << " as nonnull\n");
-      F->addAttribute(AttributeList::ReturnIndex, Attribute::NonNull);
+      F->addRetAttr(Attribute::NonNull);
       ++NumNonNullReturn;
       MadeChange = true;
     }

llvm/lib/Transforms/IPO/WholeProgramDevirt.cpp

@@ -1288,7 +1288,7 @@ void DevirtModule::tryICallBranchFunnel(
                           M.getDataLayout().getProgramAddressSpace(),
                           "branch_funnel", &M);
   }
-  JT->addAttribute(1, Attribute::Nest);
+  JT->addParamAttr(0, Attribute::Nest);
 
   std::vector<Value *> JTArgs;
   JTArgs.push_back(JT->arg_begin());

llvm/lib/Transforms/Instrumentation/AddressSanitizer.cpp

@@ -2133,8 +2133,7 @@ Instruction *ModuleAddressSanitizer::CreateAsanModuleDtor(Module &M) {
   AsanDtorFunction = Function::createWithDefaultAttr(
       FunctionType::get(Type::getVoidTy(*C), false),
       GlobalValue::InternalLinkage, 0, kAsanModuleDtorName, &M);
-  AsanDtorFunction->addAttribute(AttributeList::FunctionIndex,
-                                 Attribute::NoUnwind);
+  AsanDtorFunction->addFnAttr(Attribute::NoUnwind);
   // Ensure Dtor cannot be discarded, even if in a comdat.
   appendToUsed(M, {AsanDtorFunction});
   BasicBlock *AsanDtorBB = BasicBlock::Create(*C, "", AsanDtorFunction);

llvm/lib/Transforms/Utils/BuildLibCalls.cpp

@@ -98,7 +98,7 @@ static bool setDoesNotThrow(Function &F) {
 static bool setRetDoesNotAlias(Function &F) {
   if (F.hasRetAttribute(Attribute::NoAlias))
     return false;
-  F.addAttribute(AttributeList::ReturnIndex, Attribute::NoAlias);
+  F.addRetAttr(Attribute::NoAlias);
   ++NumNoAlias;
   return true;
 }
@@ -146,7 +146,7 @@ static bool setSignExtendedArg(Function &F, unsigned ArgNo) {
 static bool setRetNoUndef(Function &F) {
   if (!F.getReturnType()->isVoidTy() &&
       !F.hasRetAttribute(Attribute::NoUndef)) {
-    F.addAttribute(AttributeList::ReturnIndex, Attribute::NoUndef);
+    F.addRetAttr(Attribute::NoUndef);
     ++NumNoUndef;
     return true;
   }

llvm/lib/Transforms/Utils/ModuleUtils.cpp

@@ -125,7 +125,7 @@ Function *llvm::createSanitizerCtor(Module &M, StringRef CtorName) {
   Function *Ctor = Function::createWithDefaultAttr(
       FunctionType::get(Type::getVoidTy(M.getContext()), false),
       GlobalValue::InternalLinkage, 0, CtorName, &M);
-  Ctor->addAttribute(AttributeList::FunctionIndex, Attribute::NoUnwind);
+  Ctor->addFnAttr(Attribute::NoUnwind);
   BasicBlock *CtorBB = BasicBlock::Create(M.getContext(), "", Ctor);
   ReturnInst::Create(M.getContext(), CtorBB);
   // Ensure Ctor cannot be discarded, even if in a comdat.