lint ImproperCTypes: change what elements are being checked [...]

- do not check ADT definitions themselves, it turns out `repr(C)` is not
  a strong enough signal to determine if something is designed for FFIs
- however, start checking static variables with `#[no_mangle]` or
  `#[export_name=_]`, even if that's not a perfect signal due to the
  lack of specified ABI
- some changes to the LLVM codegen so it can be seen as FFI-safe

Author: niacdoial

compiler/rustc_codegen_llvm/src/back/write.rs

@@ -462,10 +462,11 @@ fn report_inline_asm(
     cgcx.diag_emitter.inline_asm_error(span, msg, level, source);
 }
 
-unsafe extern "C" fn diagnostic_handler(info: &DiagnosticInfo, user: *mut c_void) {
+unsafe extern "C" fn diagnostic_handler(info: Option<&DiagnosticInfo>, user: *mut c_void) {
     if user.is_null() {
         return;
     }
+    let info = info.unwrap();
     let (cgcx, dcx) =
         unsafe { *(user as *const (&CodegenContext<LlvmCodegenBackend>, DiagCtxtHandle<'_>)) };
 

compiler/rustc_codegen_llvm/src/llvm/enzyme_ffi.rs

@@ -6,7 +6,9 @@ use libc::{c_char, c_uint};
 use super::MetadataKindId;
 use super::ffi::{AttributeKind, BasicBlock, Metadata, Module, Type, Value};
 use crate::llvm::Bool;
+use crate::wrap_returns_in_options;
 
+wrap_returns_in_options! {
 #[link(name = "llvm-wrapper", kind = "static")]
 unsafe extern "C" {
     // Enzyme
@@ -15,7 +17,7 @@ unsafe extern "C" {
     pub(crate) fn LLVMRustGetLastInstruction<'a>(BB: &BasicBlock) -> Option<&'a Value>;
     pub(crate) fn LLVMRustDIGetInstMetadata(I: &Value) -> Option<&Metadata>;
     pub(crate) fn LLVMRustEraseInstFromParent(V: &Value);
-    pub(crate) fn LLVMRustGetTerminator<'a>(B: &BasicBlock) -> &'a Value;
+    |wrap pub(crate) fn LLVMRustGetTerminator<'a>(B: &BasicBlock) -> &'a Value;
     pub(crate) fn LLVMRustVerifyFunction(V: &Value, action: LLVMRustVerifierFailureAction) -> Bool;
     pub(crate) fn LLVMRustHasAttributeAtIndex(V: &Value, i: c_uint, Kind: AttributeKind) -> bool;
     pub(crate) fn LLVMRustGetArrayNumElements(Ty: &Type) -> u64;
@@ -39,10 +41,11 @@ unsafe extern "C" {
     pub(crate) fn LLVMDumpModule(M: &Module);
     pub(crate) fn LLVMDumpValue(V: &Value);
     pub(crate) fn LLVMGetFunctionCallConv(F: &Value) -> c_uint;
-    pub(crate) fn LLVMGetReturnType(T: &Type) -> &Type;
+    |wrap pub(crate) fn LLVMGetReturnType(T: &Type) -> &Type;
     pub(crate) fn LLVMGetParams(Fnc: &Value, parms: *mut &Value);
     pub(crate) fn LLVMGetNamedFunction(M: &Module, Name: *const c_char) -> Option<&Value>;
 }
+}
 
 #[repr(C)]
 #[derive(Copy, Clone, PartialEq)]