perf(object): #6812 w16 — per-site builder identity, learned width, and compile-time width hints beat node on overflow-slot writes

changelog.d/6812-w16-builder-identity.md

@@ -0,0 +1 @@
+perf(object): #6812 w16 — builder-pattern objects get a learnable per-site identity. Empty object literals lower to a unique 0-field anon-shape class per source site (content-addressed on file + offset), so the runtime's learned inline sizing and the static-key write PIC admit `{}`-built objects; the compiled-`new` allocator consumes the learned high-water width. A constant-bounded dynamic-key build loop additionally proves its width at compile time (`Class::alloc_width_hint`), right-sizing even the first instance so arrays of builder objects stay uniform and whole-loop clone eligible. w16 (overflow-slot writes): 173× slower than node → beats node.

crates/perry-codegen/src/codegen/mod.rs

@@ -422,6 +422,9 @@ pub fn compile_module(hir: &HirModule, opts: CompileOptions) -> Result<Vec<u8>>
         let stub = perry_hir::Class {
             id: 0, // imported — no local ClassId
             name: effective_name.to_string(),
+            // #6812: width hints don't cross module metadata; imported stubs
+            // fall back to runtime learned sizing.
+            alloc_width_hint: 0,
             type_params: Vec::new(),
             extends: None,
             extends_name: ic.parent_name.clone(),

crates/perry-codegen/src/collectors/class_accessors.rs

@@ -109,6 +109,7 @@ mod tests {
             is_exported: false,
             aliases: Vec::new(),
             is_nested: false,
+            alloc_width_hint: 0,
             static_accessor_names: Vec::new(),
             static_accessor_fn_ids: Vec::new(),
         }

crates/perry-codegen/src/collectors/scalar_method_dispatch.rs

@@ -465,6 +465,7 @@ mod tests {
             decorators: Vec::new(),
             is_exported: false,
             is_nested: false,
+            alloc_width_hint: 0,
             aliases: Vec::new(),
         }
     }

crates/perry-codegen/src/collectors/this_as_value.rs

@@ -536,6 +536,7 @@ mod tests {
             is_exported: false,
             aliases: Vec::new(),
             is_nested: false,
+            alloc_width_hint: 0,
             static_accessor_names: Vec::new(),
             static_accessor_fn_ids: Vec::new(),
         }

crates/perry-codegen/src/lower_call/buffer_intrinsic.rs

@@ -569,6 +569,7 @@ mod shadow_scan_tests {
             is_exported: false,
             aliases: Vec::new(),
             is_nested: false,
+            alloc_width_hint: 0,
         }
     }
 

crates/perry-codegen/src/lower_call/new.rs

@@ -360,6 +360,16 @@ fn lower_new_impl(
     if let Some(&authoritative) = ctx.class_field_counts.get(class_name) {
         field_count = authoritative;
     }
+    // #6812 (w16): a per-site empty-literal anon-shape class may carry a
+    // compile-time proven builder width. Allocate that many inline slots so
+    // the FIRST instance of the site is as wide as the runtime-learned
+    // resizes make every later one — a lone under-sized first instance
+    // permanently vetoes whole-loop clone eligibility for arrays built at
+    // the site. Capacity only: the keys array stays authoritative for
+    // enumeration, and the runtime treats header field_count as alloc_limit.
+    if class.alloc_width_hint > field_count {
+        field_count = class.alloc_width_hint;
+    }
 
     // Allocate the object with the per-class id and (if applicable)
     // parent class id, so the runtime registers the inheritance

crates/perry-codegen/src/type_analysis_tests.rs

@@ -214,6 +214,7 @@ fn hir_inferred_types_reuse_codegen_contextual_class_facts() {
         decorators: Vec::new(),
         is_exported: false,
         is_nested: false,
+        alloc_width_hint: 0,
         aliases: Vec::new(),
     };
     let widget = perry_hir::Class {
@@ -284,6 +285,7 @@ fn hir_inferred_types_reuse_codegen_contextual_class_facts() {
         decorators: Vec::new(),
         is_exported: false,
         is_nested: false,
+        alloc_width_hint: 0,
         aliases: Vec::new(),
     };
     let classes = HashMap::from([("Base".to_string(), &base), ("Widget".to_string(), &widget)]);

crates/perry-codegen/tests/class_keys_gc_root.rs

@@ -120,6 +120,7 @@ fn module_with_declared_field_class() -> Module {
             decorators: Vec::new(),
             is_exported: false,
             is_nested: false,
+            alloc_width_hint: 0,
             aliases: Vec::new(),
         }],
         interfaces: Vec::new(),

crates/perry-codegen/tests/constructor_recursion.rs

@@ -122,6 +122,7 @@ fn module_with_recursive_constructor_return() -> Module {
             is_exported: false,
             aliases: Vec::new(),
             is_nested: false,
+            alloc_width_hint: 0,
         }],
         interfaces: Vec::new(),
         type_aliases: Vec::new(),

crates/perry-codegen/tests/native_proof_buffer_views.rs

@@ -254,6 +254,7 @@ fn class(id: u32, name: &str, fields: Vec<ClassField>) -> Class {
         is_exported: false,
         aliases: Vec::new(),
         is_nested: false,
+        alloc_width_hint: 0,
     }
 }
 
@@ -1554,9 +1555,16 @@ fn native_owned_uint8array_get_fallback_uses_uint8array_helper() {
             })),
         ],
     );
+    // Codegen migrated the disposed-view fallback from `js_uint8array_get`
+    // to `js_uint8array_index_get_value` (#6088-era JS-value getter), which
+    // validates the address against the typed-array kind registry before any
+    // dereference and returns undefined for dead views — the memory-safety
+    // property this test exists to pin. The suite was not CI-selected when
+    // that landed, so the old helper name went stale here.
     assert!(
-        ir.contains("call i32 @js_uint8array_get"),
-        "disposed native Uint8Array fallback should call js_uint8array_get:\n{ir}"
+        ir.contains("call double @js_uint8array_index_get_value"),
+        "disposed native Uint8Array fallback should call the registry-validating \
+         js_uint8array_index_get_value:\n{ir}"
     );
     assert!(
         !ir.contains("call i32 @js_buffer_get"),

crates/perry-codegen/tests/native_proof_regressions.rs

@@ -258,6 +258,7 @@ fn class(id: u32, name: &str, fields: Vec<ClassField>) -> Class {
         is_exported: false,
         aliases: Vec::new(),
         is_nested: false,
+        alloc_width_hint: 0,
     }
 }
 

crates/perry-codegen/tests/private_guard_declaring_class.rs

@@ -55,6 +55,7 @@ fn class(id: u32, name: &str) -> Class {
         is_exported: false,
         aliases: Vec::new(),
         is_nested: false,
+        alloc_width_hint: 0,
     }
 }
 

crates/perry-codegen/tests/static_symbol_hygiene.rs

@@ -117,6 +117,7 @@ fn class_with_static(id: u32, value: f64) -> Class {
         is_exported: false,
         aliases: Vec::new(),
         is_nested: false,
+        alloc_width_hint: 0,
     }
 }
 

crates/perry-codegen/tests/typed_feedback.rs

@@ -134,6 +134,7 @@ fn class(id: u32, name: &str, fields: Vec<ClassField>) -> Class {
         is_exported: false,
         aliases: Vec::new(),
         is_nested: false,
+        alloc_width_hint: 0,
     }
 }
 
@@ -217,11 +218,27 @@ fn typed_feedback_trace_dump_runs_before_entry_return() {
     ));
 
     assert!(ir.contains("declare void @js_typed_feedback_maybe_dump_trace()"));
-    let dump_pos = ir
-        .rfind("call void @js_typed_feedback_maybe_dump_trace()")
-        .expect("entry should call typed-feedback trace dump");
-    let ret_pos = ir.rfind("ret i32 0").expect("entry should return i32 0");
-    assert!(dump_pos < ret_pos);
+    // The entry epilogue now has TWO exit paths: the host-return path
+    // (`ret i32 0`) and the event-loop exit path, which returns the dynamic
+    // `js_process_pending_exit_code` result (`ret i32 %rN`). The old
+    // rfind(dump) < rfind("ret i32 0") comparison broke the day the second
+    // path appeared — its dump call sits after the literal `ret i32 0`. The
+    // real invariant is stronger: EVERY entry return must be immediately
+    // preceded by the trace dump, so no exit path can skip the dump.
+    let mut ret_count = 0;
+    let mut search_from = 0;
+    while let Some(rel) = ir[search_from..].find("ret i32") {
+        let ret_pos = search_from + rel;
+        ret_count += 1;
+        let preceding = &ir[ret_pos.saturating_sub(200)..ret_pos];
+        assert!(
+            preceding.contains("call void @js_typed_feedback_maybe_dump_trace()"),
+            "entry return at byte {ret_pos} is not preceded by the typed-feedback \
+             trace dump:\n...{preceding}"
+        );
+        search_from = ret_pos + 1;
+    }
+    assert!(ret_count >= 1, "entry should return i32");
 }
 
 #[test]

crates/perry-codegen/tests/typed_shape_descriptor.rs

@@ -91,6 +91,7 @@ fn class(id: u32, name: &str, fields: Vec<ClassField>) -> Class {
         is_exported: false,
         aliases: Vec::new(),
         is_nested: false,
+        alloc_width_hint: 0,
     }
 }
 

crates/perry-hir/src/analysis/value_types_tests.rs

@@ -622,6 +622,7 @@ fn seeds_contextual_class_and_enum_facts_from_module() {
         decorators: Vec::new(),
         is_exported: false,
         is_nested: false,
+        alloc_width_hint: 0,
         aliases: Vec::new(),
     });
 
@@ -694,6 +695,7 @@ fn infers_named_class_and_interface_property_facts() {
         decorators: Vec::new(),
         is_exported: false,
         is_nested: false,
+        alloc_width_hint: 0,
         aliases: Vec::new(),
     });
     module.classes.push(Class {
@@ -718,6 +720,7 @@ fn infers_named_class_and_interface_property_facts() {
         decorators: Vec::new(),
         is_exported: false,
         is_nested: false,
+        alloc_width_hint: 0,
         aliases: Vec::new(),
     });
     module.interfaces.push(Interface {
@@ -1661,6 +1664,7 @@ fn resolves_this_and_super_in_class_context() {
         decorators: Vec::new(),
         is_exported: false,
         is_nested: false,
+        alloc_width_hint: 0,
         aliases: Vec::new(),
     });
     module.classes.push(Class {
@@ -1685,6 +1689,7 @@ fn resolves_this_and_super_in_class_context() {
         decorators: Vec::new(),
         is_exported: false,
         is_nested: false,
+        alloc_width_hint: 0,
         aliases: Vec::new(),
     });
 

crates/perry-hir/src/ir/decl.rs

@@ -258,6 +258,16 @@ pub struct Class {
     /// inside a turbopack factory threw at module init). Codegen
     /// (`init_static_fields_*`) skips module-init static init for these.
     pub is_nested: bool,
+    /// #6812 (w16): minimum inline slot count to allocate for instances,
+    /// beyond `fields.len()`. Set only on per-site empty-literal anon-shape
+    /// classes when the lowering can prove the builder's final width (e.g. a
+    /// `{}` declarator followed by a constant-bounded single-write build
+    /// loop), so even the FIRST instance allocates every field inline
+    /// instead of spilling to the overflow side-table and permanently
+    /// poisoning whole-loop clone eligibility for arrays built at that
+    /// site. Pure capacity: does not add fields, keys, or enumeration
+    /// entries. 0 = no hint.
+    pub alloc_width_hint: u32,
 }
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]