Use lazy locals allocation in vectorcall fast path, add debug_assert bounds

youknowone · youknowone · commit 5dc8c48b27c7 · 2026-03-03T23:58:21.000+09:00
diff --git a/crates/vm/src/builtins/function.rs b/crates/vm/src/builtins/function.rs
@@ -1278,14 +1278,14 @@ pub(crate) fn vectorcall_function(
         // FAST PATH: simple positional-only call, exact arg count.
         // Move owned args directly into fastlocals — no clone needed.
         let locals = if code.flags.contains(bytecode::CodeFlags::NEWLOCALS) {
-            ArgMapping::from_dict_exact(vm.ctx.new_dict())
+            None // lazy allocation — most frames never access locals dict
         } else {
-            ArgMapping::from_dict_exact(zelf.globals.clone())
+            Some(ArgMapping::from_dict_exact(zelf.globals.clone()))
         };
 
         let frame = Frame::new(
             code.to_owned(),
-            Scope::new(Some(locals), zelf.globals.clone()),
+            Scope::new(locals, zelf.globals.clone()),
             zelf.builtins.clone(),
             zelf.closure.as_ref().map_or(&[], |c| c.as_slice()),
             Some(zelf.to_owned().into()),
diff --git a/crates/vm/src/function/argument.rs b/crates/vm/src/function/argument.rs
@@ -144,6 +144,8 @@ impl FuncArgs {
         nargs: usize,
         kwnames: Option<&[PyObjectRef]>,
     ) -> Self {
+        debug_assert!(nargs <= args.len());
+        debug_assert!(kwnames.is_none_or(|kw| nargs + kw.len() <= args.len()));
         let pos_args = args[..nargs].to_vec();
         let kwargs = if let Some(names) = kwnames {
             names
@@ -173,6 +175,8 @@ impl FuncArgs {
         nargs: usize,
         kwnames: Option<&[PyObjectRef]>,
     ) -> Self {
+        debug_assert!(nargs <= args.len());
+        debug_assert!(kwnames.is_none_or(|kw| nargs + kw.len() <= args.len()));
         let kwargs = if let Some(names) = kwnames {
             let kw_count = names.len();
             names
