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BridgeJS: Optimize string encoding for JS-to-Swift crossings #10

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1930dc1
BridgeJS: Add string encoding cache for parameter and return paths
krodak May 20, 2026
4d11610
BridgeJS: Use direct string retain + encodeInto() for stack ABI paths
krodak May 20, 2026
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37 changes: 37 additions & 0 deletions Plugins/BridgeJS/Sources/BridgeJSLink/BridgeJSLink.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -339,6 +339,26 @@ public struct BridgeJSLink {
"let \(JSGlueVariableScope.reservedStorageToReturnOptionalFloat);",
"let \(JSGlueVariableScope.reservedStorageToReturnOptionalDouble);",
"let \(JSGlueVariableScope.reservedStorageToReturnOptionalHeapObject);",
"const \(JSGlueVariableScope.reservedStrEncCache) = new Map();",
"const \(JSGlueVariableScope.reservedStrEncCacheMax) = 4096;",
"function \(JSGlueVariableScope.reservedCachedEncode)(str) {",
" let encoded = \(JSGlueVariableScope.reservedStrEncCache).get(str);",
" if (encoded) {",
" \(JSGlueVariableScope.reservedStrEncCache).delete(str);",
" \(JSGlueVariableScope.reservedStrEncCache).set(str, encoded);",
" return encoded;",
" }",
" encoded = \(JSGlueVariableScope.reservedTextEncoder).encode(str);",
" if (\(JSGlueVariableScope.reservedStrEncCache).size >= \(JSGlueVariableScope.reservedStrEncCacheMax)) {",
" \(JSGlueVariableScope.reservedStrEncCache).delete(\(JSGlueVariableScope.reservedStrEncCache).keys().next().value);",
" }",
" \(JSGlueVariableScope.reservedStrEncCache).set(str, encoded);",
" return encoded;",
"}",
// Worst-case UTF-8 byte count: each UTF-16 code unit can expand
// to at most 3 bytes. Surrogate pairs (2 units) produce 4 bytes,
// so the per-unit ratio stays <= 3.
"function \(JSGlueVariableScope.reservedMaxUTF8Len)(str) { return str.length * 3; }",
"let \(JSGlueVariableScope.reservedStringStack) = [];",
"let \(JSGlueVariableScope.reservedI32Stack) = [];",
"let \(JSGlueVariableScope.reservedI64Stack) = [];",
Expand Down Expand Up @@ -396,6 +416,23 @@ public struct BridgeJSLink {
printer.write("bytes.set(source);")
}
printer.write("}")
printer.write("bjs[\"swift_js_init_memory_from_string\"] = function(sourceId, bytesPtr) {")
printer.indent {
printer.write(
"const str = \(JSGlueVariableScope.reservedSwift).\(JSGlueVariableScope.reservedMemory).getObject(sourceId);"
)
printer.write(
"\(JSGlueVariableScope.reservedSwift).\(JSGlueVariableScope.reservedMemory).release(sourceId);"
)
printer.write(
"const target = new Uint8Array(\(JSGlueVariableScope.reservedMemory).buffer, bytesPtr);"
)
printer.write(
"const result = \(JSGlueVariableScope.reservedTextEncoder).encodeInto(str, target);"
)
printer.write("return result.written;")
}
printer.write("}")
printer.write("bjs[\"swift_js_make_js_string\"] = function(ptr, len) {")
printer.indent {
printer.write(
Expand Down
21 changes: 14 additions & 7 deletions Plugins/BridgeJS/Sources/BridgeJSLink/JSGlueGen.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -24,6 +24,10 @@ final class JSGlueVariableScope {
static let reservedStorageToReturnOptionalHeapObject = "tmpRetOptionalHeapObject"
static let reservedTextEncoder = "textEncoder"
static let reservedTextDecoder = "textDecoder"
static let reservedCachedEncode = "_cachedEncode"
static let reservedStrEncCache = "_strEncCache"
static let reservedStrEncCacheMax = "_strEncCacheMax"
static let reservedMaxUTF8Len = "_maxUTF8Len"
static let reservedStringStack = "strStack"
static let reservedI32Stack = "i32Stack"
static let reservedI64Stack = "i64Stack"
Expand Down Expand Up @@ -53,6 +57,10 @@ final class JSGlueVariableScope {
reservedStorageToReturnOptionalHeapObject,
reservedTextEncoder,
reservedTextDecoder,
reservedCachedEncode,
reservedStrEncCache,
reservedStrEncCacheMax,
reservedMaxUTF8Len,
reservedStringStack,
reservedI32Stack,
reservedI64Stack,
Expand Down Expand Up @@ -263,7 +271,7 @@ struct IntrinsicJSFragment: Sendable {
let argument = arguments[0]
let bytesLabel = scope.variable("\(argument)Bytes")
let bytesIdLabel = scope.variable("\(argument)Id")
printer.write("const \(bytesLabel) = \(JSGlueVariableScope.reservedTextEncoder).encode(\(argument));")
printer.write("const \(bytesLabel) = \(JSGlueVariableScope.reservedCachedEncode)(\(argument));")
printer.write("const \(bytesIdLabel) = \(JSGlueVariableScope.reservedSwift).memory.retain(\(bytesLabel));")
return [bytesIdLabel, "\(bytesLabel).length"]
}
Expand Down Expand Up @@ -296,7 +304,7 @@ struct IntrinsicJSFragment: Sendable {
printCode: { arguments, context in
let printer = context.printer
printer.write(
"\(JSGlueVariableScope.reservedStorageToReturnBytes) = \(JSGlueVariableScope.reservedTextEncoder).encode(\(arguments[0]));"
"\(JSGlueVariableScope.reservedStorageToReturnBytes) = \(JSGlueVariableScope.reservedCachedEncode)(\(arguments[0]));"
)
return ["\(JSGlueVariableScope.reservedStorageToReturnBytes).length"]
}
Expand Down Expand Up @@ -2116,15 +2124,14 @@ struct IntrinsicJSFragment: Sendable {
printCode: { arguments, context in
let (scope, printer) = (context.scope, context.printer)
let value = arguments[0]
let bytesVar = scope.variable("bytes")
let idVar = scope.variable("id")
printer.write(
"const \(bytesVar) = \(JSGlueVariableScope.reservedTextEncoder).encode(\(value));"
"const \(idVar) = \(JSGlueVariableScope.reservedSwift).memory.retain(\(value));"
)
printer.write(
"const \(idVar) = \(JSGlueVariableScope.reservedSwift).memory.retain(\(bytesVar));"
scope.emitPushI32Parameter(
"\(JSGlueVariableScope.reservedMaxUTF8Len)(\(value))",
printer: printer
)
scope.emitPushI32Parameter("\(bytesVar).length", printer: printer)
scope.emitPushI32Parameter(idVar, printer: printer)
return []
}
Expand Down
61 changes: 39 additions & 22 deletions Plugins/BridgeJS/Tests/BridgeJSToolTests/__Snapshots__/BridgeJSLinkTests/ArrayTypes.js
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Original file line number Diff line number Diff line change
Expand Up @@ -32,6 +32,23 @@ export async function createInstantiator(options, swift) {
let tmpRetOptionalFloat;
let tmpRetOptionalDouble;
let tmpRetOptionalHeapObject;
const _strEncCache = new Map();
const _strEncCacheMax = 4096;
function _cachedEncode(str) {
let encoded = _strEncCache.get(str);
if (encoded) {
_strEncCache.delete(str);
_strEncCache.set(str, encoded);
return encoded;
}
encoded = textEncoder.encode(str);
if (_strEncCache.size >= _strEncCacheMax) {
_strEncCache.delete(_strEncCache.keys().next().value);
}
_strEncCache.set(str, encoded);
return encoded;
}
function _maxUTF8Len(str) { return str.length * 3; }
let strStack = [];
let i32Stack = [];
let i64Stack = [];
Expand Down Expand Up @@ -72,6 +89,13 @@ export async function createInstantiator(options, swift) {
const bytes = new Uint8Array(memory.buffer, bytesPtr);
bytes.set(source);
}
bjs["swift_js_init_memory_from_string"] = function(sourceId, bytesPtr) {
const str = swift.memory.getObject(sourceId);
swift.memory.release(sourceId);
const target = new Uint8Array(memory.buffer, bytesPtr);
const result = textEncoder.encodeInto(str, target);
return result.written;
}
bjs["swift_js_make_js_string"] = function(ptr, len) {
return swift.memory.retain(decodeString(ptr, len));
}
Expand Down Expand Up @@ -301,9 +325,8 @@ export async function createInstantiator(options, swift) {
arrayResult.reverse();
let ret = imports.importProcessStrings(arrayResult);
for (const elem of ret) {
const bytes = textEncoder.encode(elem);
const id = swift.memory.retain(bytes);
i32Stack.push(bytes.length);
const id = swift.memory.retain(elem);
i32Stack.push(_maxUTF8Len(elem));
i32Stack.push(id);
}
i32Stack.push(ret.length);
Expand Down Expand Up @@ -411,9 +434,8 @@ export async function createInstantiator(options, swift) {
}
i32Stack.push(nums.length);
for (const elem1 of strs) {
const bytes = textEncoder.encode(elem1);
const id = swift.memory.retain(bytes);
i32Stack.push(bytes.length);
const id = swift.memory.retain(elem1);
i32Stack.push(_maxUTF8Len(elem1));
i32Stack.push(id);
}
i32Stack.push(strs.length);
Expand Down Expand Up @@ -466,9 +488,8 @@ export async function createInstantiator(options, swift) {
},
processStringArray: function bjs_processStringArray(values) {
for (const elem of values) {
const bytes = textEncoder.encode(elem);
const id = swift.memory.retain(bytes);
i32Stack.push(bytes.length);
const id = swift.memory.retain(elem);
i32Stack.push(_maxUTF8Len(elem));
i32Stack.push(id);
}
i32Stack.push(values.length);
Expand Down Expand Up @@ -570,7 +591,7 @@ export async function createInstantiator(options, swift) {
structHelpers.Point.lower(elem);
}
i32Stack.push(points.length);
const matchingBytes = textEncoder.encode(matching);
const matchingBytes = _cachedEncode(matching);
const matchingId = swift.memory.retain(matchingBytes);
instance.exports.bjs_findFirstPoint(matchingId, matchingBytes.length);
const structValue = structHelpers.Point.lift();
Expand Down Expand Up @@ -651,9 +672,8 @@ export async function createInstantiator(options, swift) {
for (const elem of values) {
const isSome = elem != null ? 1 : 0;
if (isSome) {
const bytes = textEncoder.encode(elem);
const id = swift.memory.retain(bytes);
i32Stack.push(bytes.length);
const id = swift.memory.retain(elem);
i32Stack.push(_maxUTF8Len(elem));
i32Stack.push(id);
}
i32Stack.push(isSome);
Expand Down Expand Up @@ -807,9 +827,8 @@ export async function createInstantiator(options, swift) {
processNestedStringArray: function bjs_processNestedStringArray(values) {
for (const elem of values) {
for (const elem1 of elem) {
const bytes = textEncoder.encode(elem1);
const id = swift.memory.retain(bytes);
i32Stack.push(bytes.length);
const id = swift.memory.retain(elem1);
i32Stack.push(_maxUTF8Len(elem1));
i32Stack.push(id);
}
i32Stack.push(elem.length);
Expand Down Expand Up @@ -976,9 +995,8 @@ export async function createInstantiator(options, swift) {
}
i32Stack.push(nums.length);
for (const elem1 of strs) {
const bytes = textEncoder.encode(elem1);
const id = swift.memory.retain(bytes);
i32Stack.push(bytes.length);
const id = swift.memory.retain(elem1);
i32Stack.push(_maxUTF8Len(elem1));
i32Stack.push(id);
}
i32Stack.push(strs.length);
Expand All @@ -997,9 +1015,8 @@ export async function createInstantiator(options, swift) {
const isSome1 = b != null;
if (isSome1) {
for (const elem1 of b) {
const bytes = textEncoder.encode(elem1);
const id = swift.memory.retain(bytes);
i32Stack.push(bytes.length);
const id = swift.memory.retain(elem1);
i32Stack.push(_maxUTF8Len(elem1));
i32Stack.push(id);
}
i32Stack.push(b.length);
Expand Down
26 changes: 25 additions & 1 deletion Plugins/BridgeJS/Tests/BridgeJSToolTests/__Snapshots__/BridgeJSLinkTests/Async.js
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Original file line number Diff line number Diff line change
Expand Up @@ -19,6 +19,23 @@ export async function createInstantiator(options, swift) {
let tmpRetOptionalFloat;
let tmpRetOptionalDouble;
let tmpRetOptionalHeapObject;
const _strEncCache = new Map();
const _strEncCacheMax = 4096;
function _cachedEncode(str) {
let encoded = _strEncCache.get(str);
if (encoded) {
_strEncCache.delete(str);
_strEncCache.set(str, encoded);
return encoded;
}
encoded = textEncoder.encode(str);
if (_strEncCache.size >= _strEncCacheMax) {
_strEncCache.delete(_strEncCache.keys().next().value);
}
_strEncCache.set(str, encoded);
return encoded;
}
function _maxUTF8Len(str) { return str.length * 3; }
let strStack = [];
let i32Stack = [];
let i64Stack = [];
Expand Down Expand Up @@ -47,6 +64,13 @@ export async function createInstantiator(options, swift) {
const bytes = new Uint8Array(memory.buffer, bytesPtr);
bytes.set(source);
}
bjs["swift_js_init_memory_from_string"] = function(sourceId, bytesPtr) {
const str = swift.memory.getObject(sourceId);
swift.memory.release(sourceId);
const target = new Uint8Array(memory.buffer, bytesPtr);
const result = textEncoder.encodeInto(str, target);
return result.written;
}
bjs["swift_js_make_js_string"] = function(ptr, len) {
return swift.memory.retain(decodeString(ptr, len));
}
Expand Down Expand Up @@ -216,7 +240,7 @@ export async function createInstantiator(options, swift) {
return ret1;
},
asyncRoundTripString: function bjs_asyncRoundTripString(v) {
const vBytes = textEncoder.encode(v);
const vBytes = _cachedEncode(v);
const vId = swift.memory.retain(vBytes);
const ret = instance.exports.bjs_asyncRoundTripString(vId, vBytes.length);
const ret1 = swift.memory.getObject(ret);
Expand Down
26 changes: 25 additions & 1 deletion Plugins/BridgeJS/Tests/BridgeJSToolTests/__Snapshots__/BridgeJSLinkTests/AsyncImport.js
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Original file line number Diff line number Diff line change
Expand Up @@ -19,6 +19,23 @@ export async function createInstantiator(options, swift) {
let tmpRetOptionalFloat;
let tmpRetOptionalDouble;
let tmpRetOptionalHeapObject;
const _strEncCache = new Map();
const _strEncCacheMax = 4096;
function _cachedEncode(str) {
let encoded = _strEncCache.get(str);
if (encoded) {
_strEncCache.delete(str);
_strEncCache.set(str, encoded);
return encoded;
}
encoded = textEncoder.encode(str);
if (_strEncCache.size >= _strEncCacheMax) {
_strEncCache.delete(_strEncCache.keys().next().value);
}
_strEncCache.set(str, encoded);
return encoded;
}
function _maxUTF8Len(str) { return str.length * 3; }
let strStack = [];
let i32Stack = [];
let i64Stack = [];
Expand Down Expand Up @@ -162,6 +179,13 @@ export async function createInstantiator(options, swift) {
const bytes = new Uint8Array(memory.buffer, bytesPtr);
bytes.set(source);
}
bjs["swift_js_init_memory_from_string"] = function(sourceId, bytesPtr) {
const str = swift.memory.getObject(sourceId);
swift.memory.release(sourceId);
const target = new Uint8Array(memory.buffer, bytesPtr);
const result = textEncoder.encodeInto(str, target);
return result.written;
}
bjs["swift_js_make_js_string"] = function(ptr, len) {
return swift.memory.retain(decodeString(ptr, len));
}
Expand Down Expand Up @@ -360,7 +384,7 @@ export async function createInstantiator(options, swift) {
}
bjs["make_swift_closure_TestModule_10TestModulesSS_y"] = function(boxPtr, file, line) {
const lower_closure_TestModule_10TestModulesSS_y = function(param0) {
const param0Bytes = textEncoder.encode(param0);
const param0Bytes = _cachedEncode(param0);
const param0Id = swift.memory.retain(param0Bytes);
instance.exports.invoke_swift_closure_TestModule_10TestModulesSS_y(boxPtr, param0Id, param0Bytes.length);
if (tmpRetException) {
Expand Down
24 changes: 24 additions & 0 deletions ...ins/BridgeJS/Tests/BridgeJSToolTests/__Snapshots__/BridgeJSLinkTests/AsyncStaticImport.js
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Original file line number Diff line number Diff line change
Expand Up @@ -19,6 +19,23 @@ export async function createInstantiator(options, swift) {
let tmpRetOptionalFloat;
let tmpRetOptionalDouble;
let tmpRetOptionalHeapObject;
const _strEncCache = new Map();
const _strEncCacheMax = 4096;
function _cachedEncode(str) {
let encoded = _strEncCache.get(str);
if (encoded) {
_strEncCache.delete(str);
_strEncCache.set(str, encoded);
return encoded;
}
encoded = textEncoder.encode(str);
if (_strEncCache.size >= _strEncCacheMax) {
_strEncCache.delete(_strEncCache.keys().next().value);
}
_strEncCache.set(str, encoded);
return encoded;
}
function _maxUTF8Len(str) { return str.length * 3; }
let strStack = [];
let i32Stack = [];
let i64Stack = [];
Expand Down Expand Up @@ -161,6 +178,13 @@ export async function createInstantiator(options, swift) {
const bytes = new Uint8Array(memory.buffer, bytesPtr);
bytes.set(source);
}
bjs["swift_js_init_memory_from_string"] = function(sourceId, bytesPtr) {
const str = swift.memory.getObject(sourceId);
swift.memory.release(sourceId);
const target = new Uint8Array(memory.buffer, bytesPtr);
const result = textEncoder.encodeInto(str, target);
return result.written;
}
bjs["swift_js_make_js_string"] = function(ptr, len) {
return swift.memory.retain(decodeString(ptr, len));
}
Expand Down
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