perf(transform): scalar-replace aggregate call literals

benchmarks/compiler_output/fixtures/scalar_replacement_literals.ts

@@ -10,4 +10,29 @@ function scalarReplacementChecksum(): number {
   return values[0] + values[1] + values[2] + values.length;
 }
 
+class Position {}
+class Velocity {}
+
+let aggregateChecksum = 0;
+
+function consumeAggregate(initializers: { component: unknown }[]): void {
+  for (let i = 0; i < initializers.length; i++) {
+    const initializer = initializers[i];
+    if (initializer.component === Position) aggregateChecksum += 1;
+    if (initializer.component === Velocity) aggregateChecksum += 2;
+  }
+}
+
+function scalarAggregateCallChecksum(): number {
+  aggregateChecksum = 0;
+  const iterations = 500_000;
+  for (let i = 0; i < iterations; i++) {
+    consumeAggregate([{ component: Position }, { component: Velocity }]);
+    consumeAggregate([{ component: Position }]);
+    consumeAggregate([{ component: Velocity }]);
+  }
+  return aggregateChecksum;
+}
+
 console.log(scalarReplacementChecksum());
+console.log(scalarAggregateCallChecksum());

benchmarks/compiler_output/workloads.toml

@@ -1349,50 +1349,76 @@ function_contains = "scalarReplacementChecksum"
 regex_none = ["@js_object_get_field", "@js_object_set_field", "@js_array_get", "@js_array_set"]
 detail = "scalar-replaced literals do not use runtime property or array access helpers"
 
+[[workloads.scalar_replacement_literals.ir_checks]]
+name = "known_aggregate_call_no_object_or_array_heap_alloc"
+function_contains = "scalarAggregateCallChecksum"
+regex_none = ["@js_object_alloc", "@js_object_alloc_with_shape", "@js_array_alloc"]
+detail = "known fixed-aggregate consumers scalar-replace descriptor objects and carrier arrays"
+
+[[workloads.scalar_replacement_literals.ir_checks]]
+name = "known_aggregate_call_no_property_or_array_runtime_access"
+function_contains = "scalarAggregateCallChecksum"
+regex_none = ["@js_object_get_field", "@js_object_set_field", "@js_array_get", "@js_array_set"]
+detail = "known fixed-aggregate consumers read scalar fields without runtime aggregate helpers"
+
 [[workloads.scalar_replacement_literals.stdout_checks]]
 name = "scalar_replacement_checksum"
-equals = "17\n"
+equals = "17\n3000000\n"
 detail = "scalar-replacement fixture stdout checksum"
 
 [workloads.scalar_replacement_literals.native_rep_checks]
-function_contains = "scalarReplacementChecksum"
 allow_materialization_reasons = ["runtime_api"]
 
 [[workloads.scalar_replacement_literals.native_rep_checks.require_records]]
 name = "scalar_object_literal_store"
+source_function = "scalarReplacementChecksum"
 expr_kind = "ScalarObjectLiteralInit"
 consumer = "scalar_object_field_store"
 native_rep_name = "js_value"
 access_mode = "none"
 
 [[workloads.scalar_replacement_literals.native_rep_checks.require_records]]
 name = "scalar_object_field_get"
+source_function = "scalarReplacementChecksum"
 expr_kind = "ScalarObjectFieldGet"
 consumer = "scalar_object_field_load"
 native_rep_name = "js_value"
 access_mode = "none"
 
 [[workloads.scalar_replacement_literals.native_rep_checks.require_records]]
 name = "scalar_object_field_set"
+source_function = "scalarReplacementChecksum"
 expr_kind = "ScalarObjectFieldSet"
 consumer = "scalar_object_field_store"
 native_rep_name = "js_value"
 access_mode = "none"
 
 [[workloads.scalar_replacement_literals.native_rep_checks.require_records]]
 name = "scalar_array_literal_store"
+source_function = "scalarReplacementChecksum"
 expr_kind = "ScalarArrayLiteralInit"
 consumer = "scalar_array_element_store"
 native_rep_name = "js_value"
 access_mode = "none"
 
 [[workloads.scalar_replacement_literals.native_rep_checks.require_records]]
 name = "scalar_array_index_get"
+source_function = "scalarReplacementChecksum"
 expr_kind = "ScalarArrayIndexGet"
 consumer = "scalar_array_element_load"
 native_rep_name = "js_value"
 access_mode = "none"
 
+[[workloads.scalar_replacement_literals.native_rep_checks.require_records]]
+name = "known_aggregate_call_scalar_fields"
+source_function = "scalarAggregateCallChecksum"
+expr_kind = "ScalarAggregateFieldInit"
+consumer = "scalar_object_field_store"
+native_rep_name = "js_value"
+access_mode = "none"
+notes_contains = "carrier_array=elided"
+min = 4
+
 [workloads.width_aware_buffer_kernels]
 source = "benchmarks/compiler_output/fixtures/width_aware_buffer_kernels.ts"
 kind = "width_aware_buffer_kernels"

changelog.d/8703-scalar-aggregate-calls.md

@@ -0,0 +1,7 @@
+### Performance
+
+- Scalar-replace short arrays of non-escaping object literals passed to known,
+  bounded aggregate consumers. Their carrier arrays, descriptor objects,
+  property/index accesses, and write barriers are now eliminated after
+  conservative inlining and loop unrolling; identity-observing and otherwise
+  escaping uses continue to materialize normally.

crates/perry-codegen/src/stmt/let_stmt.rs

@@ -6,6 +6,7 @@ use super::let_buffer_views::{math_min_length_buffer_ids, register_noalias_buffe
 use super::let_stmt_facts::{
     buffer_local_alias_source, collect_scalar_class_data, native_i32_alias_source,
     note_ptr_shape_scalar_replaced, pod_view_count_source, record_pod_rejection,
+    record_scalar_aggregate_field,
 };
 use super::unused_expr::lower_unused_expr;
 use crate::expr::{
@@ -1901,6 +1902,7 @@ pub(crate) fn lower_let(
                     }
                 }
             }
+            record_scalar_aggregate_field(ctx, id, name, &v);
             v
         } else {
             String::new() // unused below; cleanup blocks check used_i32_init

crates/perry-codegen/src/stmt/let_stmt_facts.rs

@@ -7,6 +7,40 @@ use super::*;
 
 use crate::native_value::BufferAccessMode;
 
+/// #8691: the aggregate scalar-replacement transform erases the carrier array
+/// and object literals before codegen, leaving one synthetic local per field.
+/// Preserve lowering evidence for those eliminated allocations so the result
+/// remains visible to `--explain-lowering`.
+pub(super) fn record_scalar_aggregate_field(ctx: &mut FnCtx<'_>, id: u32, name: &str, value: &str) {
+    if !name.starts_with("__perry_scalar_aggregate_") {
+        return;
+    }
+    let lowered = crate::native_value::LoweredValue {
+        semantic: crate::native_value::SemanticKind::JsValue,
+        rep: crate::native_value::NativeRep::JsValue,
+        llvm_ty: DOUBLE,
+        value: value.to_string(),
+    };
+    ctx.record_lowered_value_with_access_mode(
+        "ScalarAggregateFieldInit",
+        Some(id),
+        "scalar_object_field_store",
+        &lowered,
+        None,
+        None,
+        None,
+        None,
+        false,
+        false,
+        vec![
+            format!("local={name}"),
+            "carrier_array=elided".to_string(),
+            "carrier_object=elided".to_string(),
+            "write_barrier=0".to_string(),
+        ],
+    );
+}
+
 pub(super) fn pod_view_count_source(ctx: &FnCtx<'_>, expr: &perry_hir::Expr) -> String {
     match expr {
         perry_hir::Expr::Integer(n) => format!("constant:{n}"),