[clang] [compiler-rt] [libcxx] [clang] Add unistd fortify checks and analyzer size constraints (PR #196499)

[Oliver Hunt via llvm-commits]

================
@@ -1270,224 +1388,324 @@ void Sema::checkFortifiedBuiltinMemoryFunction(FunctionDecl *FD,
     return FunctionName.str();
   };
 
-  switch (BuiltinID) {
-  default:
-    return;
-  case Builtin::BI__builtin_strcat:
-  case Builtin::BIstrcat:
-  case Builtin::BI__builtin_stpcpy:
-  case Builtin::BIstpcpy:
-  case Builtin::BI__builtin_strcpy:
-  case Builtin::BIstrcpy: {
-    DiagID = diag::warn_fortify_strlen_overflow;
-    SourceSize = ComputeStrLenArgument(1);
+  if (LibC == LibCDispatch::Read) {
----------------
ojhunt wrote:

I _think_ if you did actually use a meta type rather than a function type this could be cleaned up as well, e.g

```cpp
struct LibcFuncType {
   QualType ExpectedReturn;
   SmallVec<QualType> Params;
   std::optional<unsigned> SourceSizeIdx;
   std::optional<unsigned> MaxOperationSizeIdx;
   std::optional<unsigned> DestinationSizeIdx;
}
```

As your expected "function type" would make this logic become

```cpp
if (LibC) {
  if (auto SrcSizeIdx = libcFuncType.SourceSizeIdx)
  SourceSize = ComputeSizeArgument(*SrcSizeIdx);
...
```

Maybe the enum itself could be dropped even.

https://github.com/llvm/llvm-project/pull/196499