Lower autodiff functions using instrinsics

Author: Sa4dUs

compiler/rustc_codegen_llvm/src/intrinsic.rs

@@ -187,6 +187,9 @@ impl<'ll, 'tcx> IntrinsicCallBuilderMethods<'tcx> for Builder<'_, 'll, 'tcx> {
                     &[ptr, args[1].immediate()],
                 )
             }
+            _ if tcx.has_attr(def_id, sym::rustc_autodiff) => {
+                return Err(ty::Instance::new_raw(def_id, instance.args));
+            }
             sym::is_val_statically_known => {
                 if let OperandValue::Immediate(imm) = args[0].val {
                     self.call_intrinsic(

compiler/rustc_hir_analysis/src/check/intrinsic.rs

@@ -170,6 +170,8 @@ pub(crate) fn check_intrinsic_type(
         }
     };
 
+    let has_autodiff = tcx.has_attr(intrinsic_id, sym::rustc_autodiff);
+
     let bound_vars = tcx.mk_bound_variable_kinds(&[
         ty::BoundVariableKind::Region(ty::BoundRegionKind::Anon),
         ty::BoundVariableKind::Region(ty::BoundRegionKind::Anon),
@@ -197,6 +199,17 @@ pub(crate) fn check_intrinsic_type(
     let safety = intrinsic_operation_unsafety(tcx, intrinsic_id);
     let n_lts = 0;
     let (n_tps, n_cts, inputs, output) = match intrinsic_name {
+        _ if has_autodiff => {
+            let sig = tcx.fn_sig(intrinsic_id.to_def_id());
+            let sig = sig.skip_binder();
+            let n_tps = generics.own_counts().types;
+            let n_cts = generics.own_counts().consts;
+
+            let inputs = sig.skip_binder().inputs().to_vec();
+            let output = sig.skip_binder().output();
+
+            (n_tps, n_cts, inputs, output)
+        }
         sym::abort => (0, 0, vec![], tcx.types.never),
         sym::unreachable => (0, 0, vec![], tcx.types.never),
         sym::breakpoint => (0, 0, vec![], tcx.types.unit),