[clang] [RFC][Clang] Enable custom type checking for printf (PR #86801)

[Vikram Hegde via cfe-commits]

vikramRH wrote:

Thanks for the comments @AaronBallman. The core issue here is that the current builtin handling design does not allow multiple overloads for the same identifier to coexist  (ref. https://github.com/llvm/llvm-project/blob/eacda36c7dd842cb15c0c954eda74b67d0c73814/clang/include/clang/Basic/Builtins.h#L66), unless the builtins are defined in target specific namespaces which is what I tried in my original patch . If we want change this approach, I currently think of couple of ways at a top level
1. As you said, we could have OCL specific LibBuiltin and LangBuiltin TableGen classes (and corresponding macros in Buitlins.inc). To make this work they would need new builtin ID's  of different form (say "BI_OCL##<identifier>"). This is very Language specific.
2. Probably change the current Builtin Info structure to allow vector of possible signatures for an identifier. The builtin type decoder could choose the appropriate signature based on LangOpt. (This wording is vague and could be a separate discussion in itself )

either way, changes in current design are required. printf is the only current use case I know that can benefit out of this (since OpenCL v1.2 s6.9.f says other library functions defined in C standard header are not available ,so 🤷‍♂️  ). But I guess we could have more use cases in future. can this be a separate discussion ? This patch would unblock my current work for now. 
 


https://github.com/llvm/llvm-project/pull/86801