Update compiler/rustc_codegen_llvm/src/builder.rs

Co-authored-by: David Wood <agile.lion3441@fuligin.ink>

Author: ZuseZ4

compiler/rustc_codegen_llvm/src/builder.rs

@@ -48,16 +48,15 @@ fn get_params(fnc: &Value) -> Vec<&Value> {
     }
 }
 
-// The lowering of one `#[autodiff]` macro happens in multiple steps.
-// First we transalte generate a new dummy function, who's llvm-ir we now have as outer_fn.
-// We kept track of the original function to which the `#[autodiff]` macro was applied to, which we
-// now have as fn_to_diff. In our current implementation, we use the enzyme pass to carry out the
-// differentiation, following naming and calling conventions documented here: <https://enzyme.mit.edu/getting_started/CallingConvention/>
-//
-// Our `outer_fn` had some dummy code inserted at higher levels, so we first remove most of the
-// existing body. We then insert an `__enzyme_<autodiff/fwddiff>_<unique_id>` call, which the pass
-// will then pick up. FIXME(ZuseZ4): We will later want to upstream safety checks to the `outer_fn`,
-// in order to cover some assumptions of enzyme/autodiff, which could lead to UB otherwise.
+/// When differentiating `fn_to_diff`, take a `outer_fn` and generate another
+/// function with expected naming and calling conventions[^1] which will be
+/// discovered by the enzyme LLVM pass and its body populated with the differentiated
+/// `fn_to_diff`. `outer_fn` is then modified to have a call to the generated
+/// function and handle the differences between the Rust calling convention and
+/// Enzyme.
+/// [^1]: <https://enzyme.mit.edu/getting_started/CallingConvention/> 
+// FIXME(ZuseZ4): `outer_fn` should include upstream safety checks to
+// cover some assumptions of enzyme/autodiff, which could lead to UB otherwise.
 pub(crate) fn generate_enzyme_call<'ll>(
     llmod: &'ll llvm::Module,
     llcx: &'ll llvm::Context,