[clang] [llvm] [X86] Enhance kCFI type IDs with a 3-bit arity indicator. (PR #117121)

[Scott Constable via llvm-commits]

================
@@ -208,10 +209,34 @@ void llvm::setKCFIType(Module &M, Function &F, StringRef MangledType) {
   std::string Type = MangledType.str();
   if (M.getModuleFlag("cfi-normalize-integers"))
     Type += ".normalized";
+
+  uint32_t OutHash = static_cast<uint32_t>(llvm::xxHash64(Type));
+  auto T = Triple(Twine(M.getTargetTriple()));
+  if (T.isX86() && T.isArch64Bit() && T.isOSLinux()) {
+    // Estimate the function's arity (i.e., the number of arguments) at the ABI
+    // level by counting the number of parameters that are likely to be passed
+    // as registers, such as pointers and 64-bit (or smaller) integers. The
+    // Linux x86-64 ABI allows up to 6 parameters to be passed in GPRs.
+    // Additional parameters or parameters larger than 64 bits may be passed on
+    // the stack, in which case the arity is denoted as 7.
+    size_t NumParams = F.arg_size();
+    bool MayHaveStackArgs = NumParams > 6;
+
+    for (unsigned int i = 0; !MayHaveStackArgs && i < NumParams; ++i) {
+      const llvm::Type *PT = F.getArg(i)->getType();
+      if (!(PT->isPointerTy() || PT->getIntegerBitWidth() <= 64))
----------------
scottconstable wrote:

Is this condition equivalent to what I wrote in `CodeGenModule::CreateKCFITypeId` with `typeof(*PT) = clang::Type`? Specifically:
```
      if (!(PT->isPointerType() || (PT->isIntegralOrEnumerationType() &&
                                    getContext().getTypeSize(PT) <= 64)))
```

https://github.com/llvm/llvm-project/pull/117121