BridgeJS: Optimize numeric array transfer with bulk TypedArray copy

Add bridgeJSStackPushAsArray/bridgeJSStackPopAsArray specialization
points to _BridgedSwiftStackType protocol. Numeric types override
bridgeJSStackPushAsArray with bulk TypedArray transfer via
swift_js_push_typed_array. Array.bridgeJSStackPush() delegates to
Element.bridgeJSStackPushAsArray() — no codegen changes needed.

JS arrayLift uses -1 count discriminator to detect bulk path and
pops pre-built Array from taStack instead of element-by-element.

Non-numeric arrays use the default element-by-element implementation.

Author: krodak

Plugins/BridgeJS/Sources/BridgeJSLink/BridgeJSLink.swift

@@ -347,6 +347,7 @@ public struct BridgeJSLink {
             "let \(JSGlueVariableScope.reservedF32Stack) = [];",
             "let \(JSGlueVariableScope.reservedF64Stack) = [];",
             "let \(JSGlueVariableScope.reservedPointerStack) = [];",
+            "let taStack = [];",
             "const \(JSGlueVariableScope.reservedEnumHelpers) = {};",
             "const \(JSGlueVariableScope.reservedStructHelpers) = {};",
             "",
@@ -489,6 +490,21 @@ public struct BridgeJSLink {
                     printer.write("return \(JSGlueVariableScope.reservedI64Stack).pop();")
                 }
                 printer.write("}")
+                // Typed array constructors indexed by kind (must match _BridgedNumericArrayKind)
+                printer.write(
+                    "const taCtors = [Int8Array, Uint8Array, Int16Array, Uint16Array, Int32Array, Uint32Array, Float32Array, Float64Array];"
+                )
+                printer.write("bjs[\"swift_js_push_typed_array\"] = function(kind, ptr, count) {")
+                printer.indent {
+                    printer.write("const Ctor = taCtors[kind];")
+                    printer.write("const byteLen = count * Ctor.BYTES_PER_ELEMENT;")
+                    // slice() copies the bytes into a new ArrayBuffer that is properly aligned
+                    printer.write(
+                        "const copy = \(JSGlueVariableScope.reservedMemory).buffer.slice(ptr, ptr + byteLen);"
+                    )
+                    printer.write("taStack.push(Array.from(new Ctor(copy)));")
+                }
+                printer.write("}")
                 if !allStructs.isEmpty {
                     for structDef in allStructs {
                         printer.write("bjs[\"swift_js_struct_lower_\(structDef.abiName)\"] = function(objectId) {")

Plugins/BridgeJS/Sources/BridgeJSLink/JSGlueGen.swift

@@ -1888,28 +1888,43 @@ struct IntrinsicJSFragment: Sendable {
         )
     }
 
-    /// Lifts an array from Swift to JS by popping elements from stacks
+    /// Lifts an array from Swift to JS by popping elements from stacks.
+    ///
+    /// When the count discriminator is `-1`, the Swift side used the bulk
+    /// typed-array push path and the result is already on `taStack`.
+    /// Otherwise, elements are popped one-by-one from the typed stacks.
     static func arrayLift(elementType: BridgeType) throws -> IntrinsicJSFragment {
         return IntrinsicJSFragment(
             parameters: [],
             printCode: { arguments, context in
                 let (scope, printer) = (context.scope, context.printer)
                 let resultVar = scope.variable("arrayResult")
                 let lenVar = scope.variable("arrayLen")
-                let iVar = scope.variable("i")
 
                 printer.write("const \(lenVar) = \(scope.popI32());")
-                printer.write("const \(resultVar) = [];")
-                printer.write("for (let \(iVar) = 0; \(iVar) < \(lenVar); \(iVar)++) {")
+                printer.write("let \(resultVar);")
+                printer.write("if (\(lenVar) === -1) {")
+                printer.indent {
+                    // Bulk path: Swift pushed a typed array onto taStack
+                    printer.write("\(resultVar) = taStack.pop();")
+                }
+                printer.write("} else {")
                 try printer.indent {
-                    let elementFragment = try stackLiftFragment(elementType: elementType)
-                    let elementResults = try elementFragment.printCode([], context)
-                    if let elementExpr = elementResults.first {
-                        printer.write("\(resultVar).push(\(elementExpr));")
+                    // Element-by-element path (original behavior)
+                    let iVar = scope.variable("i")
+                    printer.write("\(resultVar) = [];")
+                    printer.write("for (let \(iVar) = 0; \(iVar) < \(lenVar); \(iVar)++) {")
+                    try printer.indent {
+                        let elementFragment = try stackLiftFragment(elementType: elementType)
+                        let elementResults = try elementFragment.printCode([], context)
+                        if let elementExpr = elementResults.first {
+                            printer.write("\(resultVar).push(\(elementExpr));")
+                        }
                     }
+                    printer.write("}")
+                    printer.write("\(resultVar).reverse();")
                 }
                 printer.write("}")
-                printer.write("\(resultVar).reverse();")
                 return [resultVar]
             }
         )