remove outdated *First autodiff variants for higher-order ad

Author: ZuseZ4

Diff for: compiler/rustc_ast/src/expand/autodiff_attrs.rs

@@ -30,14 +30,6 @@ pub enum DiffMode {
     Forward,
     /// The target function, to be created using reverse mode AD.
     Reverse,
-    /// The target function, to be created using forward mode AD.
-    /// This target function will also be used as a source for higher order derivatives,
-    /// so compute it before all Forward/Reverse targets and optimize it through llvm.
-    ForwardFirst,
-    /// The target function, to be created using reverse mode AD.
-    /// This target function will also be used as a source for higher order derivatives,
-    /// so compute it before all Forward/Reverse targets and optimize it through llvm.
-    ReverseFirst,
 }
 
 /// Dual and Duplicated (and their Only variants) are getting lowered to the same Enzyme Activity.
@@ -92,10 +84,10 @@ pub struct AutoDiffAttrs {
 
 impl DiffMode {
     pub fn is_rev(&self) -> bool {
-        matches!(self, DiffMode::Reverse | DiffMode::ReverseFirst)
+        matches!(self, DiffMode::Reverse)
     }
     pub fn is_fwd(&self) -> bool {
-        matches!(self, DiffMode::Forward | DiffMode::ForwardFirst)
+        matches!(self, DiffMode::Forward)
     }
 }
 
@@ -106,8 +98,6 @@ impl Display for DiffMode {
             DiffMode::Source => write!(f, "Source"),
             DiffMode::Forward => write!(f, "Forward"),
             DiffMode::Reverse => write!(f, "Reverse"),
-            DiffMode::ForwardFirst => write!(f, "ForwardFirst"),
-            DiffMode::ReverseFirst => write!(f, "ReverseFirst"),
         }
     }
 }
@@ -125,12 +115,12 @@ pub fn valid_ret_activity(mode: DiffMode, activity: DiffActivity) -> bool {
     match mode {
         DiffMode::Error => false,
         DiffMode::Source => false,
-        DiffMode::Forward | DiffMode::ForwardFirst => {
+        DiffMode::Forward => {
             activity == DiffActivity::Dual
                 || activity == DiffActivity::DualOnly
                 || activity == DiffActivity::Const
         }
-        DiffMode::Reverse | DiffMode::ReverseFirst => {
+        DiffMode::Reverse => {
             activity == DiffActivity::Const
                 || activity == DiffActivity::Active
                 || activity == DiffActivity::ActiveOnly
@@ -166,10 +156,10 @@ pub fn valid_input_activity(mode: DiffMode, activity: DiffActivity) -> bool {
     return match mode {
         DiffMode::Error => false,
         DiffMode::Source => false,
-        DiffMode::Forward | DiffMode::ForwardFirst => {
+        DiffMode::Forward => {
             matches!(activity, Dual | DualOnly | Const)
         }
-        DiffMode::Reverse | DiffMode::ReverseFirst => {
+        DiffMode::Reverse => {
             matches!(activity, Active | ActiveOnly | Duplicated | DuplicatedOnly | Const)
         }
     };
@@ -200,8 +190,6 @@ impl FromStr for DiffMode {
             "Source" => Ok(DiffMode::Source),
             "Forward" => Ok(DiffMode::Forward),
             "Reverse" => Ok(DiffMode::Reverse),
-            "ForwardFirst" => Ok(DiffMode::ForwardFirst),
-            "ReverseFirst" => Ok(DiffMode::ReverseFirst),
             _ => Err(()),
         }
     }

Diff for: compiler/rustc_codegen_llvm/src/builder/autodiff.rs

@@ -52,8 +52,6 @@ fn generate_enzyme_call<'ll>(
     let mut ad_name: String = match attrs.mode {
         DiffMode::Forward => "__enzyme_fwddiff",
         DiffMode::Reverse => "__enzyme_autodiff",
-        DiffMode::ForwardFirst => "__enzyme_fwddiff",
-        DiffMode::ReverseFirst => "__enzyme_autodiff",
         _ => panic!("logic bug in autodiff, unrecognized mode"),
     }
     .to_string();

Diff for: compiler/rustc_codegen_ssa/src/codegen_attrs.rs

@@ -916,8 +916,6 @@ fn autodiff_attrs(tcx: TyCtxt<'_>, id: DefId) -> Option<AutoDiffAttrs> {
     let mode = match mode.as_str() {
         "Forward" => DiffMode::Forward,
         "Reverse" => DiffMode::Reverse,
-        "ForwardFirst" => DiffMode::ForwardFirst,
-        "ReverseFirst" => DiffMode::ReverseFirst,
         _ => {
             span_bug!(mode.span, "rustc_autodiff attribute contains invalid mode");
         }