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

[Phoebe Wang via cfe-commits]

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@@ -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))
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phoebewang wrote:

Sorry, I don't understand the point of indirect calls. Here `setKCFIType` has an argument `F` which never will be null. Why do we need another `getCalledFunction()`?

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