[clang] [PAC] Implement function pointer re-signing (PR #98847)

[Akira Hatanaka via cfe-commits]

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@@ -165,6 +166,88 @@ CGPointerAuthInfo CodeGenModule::getPointerAuthInfoForType(QualType T) {
   return ::getPointerAuthInfoForType(*this, T);
 }
 
+static bool isZeroConstant(llvm::Value *value) {
+  if (auto ci = dyn_cast<llvm::ConstantInt>(value))
+    return ci->isZero();
+  return false;
+}
+
+static bool equalAuthPolicies(const CGPointerAuthInfo &left,
+                              const CGPointerAuthInfo &right) {
+  if (left.isSigned() != right.isSigned())
+    return false;
+  assert(left.isSigned() && right.isSigned() &&
+         "should only be called with non-null auth policies");
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ahatanak wrote:

I moved the assertion to the beginning of the function to make it clear that at least one side has to be signed.

https://github.com/llvm/llvm-project/pull/98847