diff --git a/ptx/src/translate.rs b/ptx/src/translate.rs
index dac31a5..2b4f593 100644
--- a/ptx/src/translate.rs
+++ b/ptx/src/translate.rs
@@ -1364,12 +1364,13 @@ fn fix_builtins(
                         value: ast::ImmediateValue::U64(0),
                     }));
                 } else {
-                    let src_type = match numeric_id_defs.special_registers.get(details.arg.src) {
+                    let sreg_and_type = match numeric_id_defs.special_registers.get(details.arg.src)
+                    {
                         Some(reg) => get_sreg_id_scalar_type(numeric_id_defs, reg),
                         None => None,
                     };
-                    let (sreg_src, scalar_typ, vector_width) = match src_type {
-                        Some(x) => x,
+                    let (sreg_src, scalar_typ, vector_width) = match sreg_and_type {
+                        Some(sreg_and_type) => sreg_and_type,
                         None => {
                             result.push(Statement::LoadVar(details));
                             continue;
@@ -1409,11 +1410,9 @@ fn get_sreg_id_scalar_type(
 ) -> Option<(spirv::Word, ast::ScalarType, u8)> {
     match sreg.normalized_sreg_and_type() {
         Some((normalized_sreg, typ, vec_width)) => Some((
-            numeric_id_defs.special_registers.replace(
-                numeric_id_defs.current_id,
-                sreg,
-                normalized_sreg,
-            ),
+            numeric_id_defs
+                .special_registers
+                .get_or_add(numeric_id_defs.current_id, normalized_sreg),
             typ,
             vec_width,
         )),
@@ -4755,11 +4754,26 @@ impl SpecialRegistersMap {
     }
 
     fn builtins<'a>(&'a self) -> impl Iterator<Item = (PtxSpecialRegister, spirv::Word)> + 'a {
-        self.reg_to_id.iter().map(|(reg, id)| (*reg, *id))
+        self.reg_to_id.iter().filter_map(|(sreg, id)| {
+            if sreg.normalized_sreg_and_type().is_none() {
+                Some((*sreg, *id))
+            } else {
+                None
+            }
+        })
     }
 
     fn interface(&self) -> Vec<spirv::Word> {
-        self.id_to_reg.iter().map(|(id, _)| *id).collect::<Vec<_>>()
+        self.reg_to_id
+            .iter()
+            .filter_map(|(sreg, id)| {
+                if sreg.normalized_sreg_and_type().is_none() {
+                    Some(*id)
+                } else {
+                    None
+                }
+            })
+            .collect::<Vec<_>>()
     }
 
     fn get(&self, id: spirv::Word) -> Option<PtxSpecialRegister> {
@@ -4778,34 +4792,6 @@ impl SpecialRegistersMap {
             }
         }
     }
-
-    fn replace(
-        &mut self,
-        current_id: &mut spirv::Word,
-        old: PtxSpecialRegister,
-        new: PtxSpecialRegister,
-    ) -> spirv::Word {
-        match self.reg_to_id.entry(old) {
-            hash_map::Entry::Occupied(e) => {
-                let id = e.remove();
-                self.reg_to_id.insert(new, id);
-                id
-            }
-            hash_map::Entry::Vacant(e) => {
-                drop(e);
-                match self.reg_to_id.entry(new) {
-                    hash_map::Entry::Occupied(e) => *e.get(),
-                    hash_map::Entry::Vacant(e) => {
-                        let numeric_id = *current_id;
-                        *current_id += 1;
-                        e.insert(numeric_id);
-                        self.id_to_reg.insert(numeric_id, new);
-                        numeric_id
-                    }
-                }
-            }
-        }
-    }
 }
 
 struct GlobalStringIdResolver<'input> {