[llvm] Use Module level target-abi to assign target features for codegenerated functions. (PR #100833)

[via llvm-commits]

================
@@ -387,6 +388,25 @@ Function *Function::Create(FunctionType *Ty, LinkageTypes Linkage,
   return Create(Ty, Linkage, M.getDataLayout().getProgramAddressSpace(), N, &M);
 }
 
+StringRef Function::getDefaultTargetFeatures(const StringRef TargetABI) {
+  Triple T(getParent()->getTargetTriple());
+  StringRef attr = "";
+  if (T.isRISCV64()) {
+    if (TargetABI.equals_insensitive("lp64d"))
+      attr = "+d";
+    else if (TargetABI.equals_insensitive("lp64f"))
+      attr = "+f";
+    else if (TargetABI.equals_insensitive("lp64q"))
+      attr = "+q";
+  } else if (T.isRISCV32() && TargetABI.contains("ilp32f")) {
+    attr = "+f";
+  } else if (T.isARM() || T.isThumb()) {
+    attr = "+thumb-mode";
----------------
hiraditya wrote:

There is no guarantee that the function exists, at least it is not clear from the code in https://github.com/llvm/llvm-project/blob/main/llvm/lib/Transforms/IPO/CrossDSOCFI.cpp#L85.

```cpp
  FunctionCallee C = M.getOrInsertFunction(
      "__cfi_check", Type::getVoidTy(Ctx), Type::getInt64Ty(Ctx),
      PointerType::getUnqual(Ctx), PointerType::getUnqual(Ctx));
```

Most likely, the declaration exists  as per `void CodeGenFunction::EmitCfiCheckStub()`. It seems clang is not emitting the right ABI to begin with?

```cpp
// void CodeGenFunction::EmitCfiCheckStub()
...
  llvm::Function *F = llvm::Function::Create(
      llvm::FunctionType::get(VoidTy, {Int64Ty, VoidPtrTy, VoidPtrTy}, false),
      llvm::GlobalValue::WeakAnyLinkage, "__cfi_check", M);
  CGM.SetLLVMFunctionAttributes(GlobalDecl(), FI, F, /*IsThunk=*/false);
  CGM.SetLLVMFunctionAttributesForDefinition(nullptr, F);
  F->setAlignment(llvm::Align(4096));
```

https://github.com/llvm/llvm-project/pull/100833