By setting Options::forceDebuggerBytecodeGeneration() = true to force the BytecodeGenerator to generate debugger friendly bytecode, the JSC stress tests now fails as follows: ** The following JSC stress test failures have been introduced: jsc-layout-tests.yaml/js/script-tests/arguments-iterator.js.layout jsc-layout-tests.yaml/js/script-tests/arguments-iterator.js.layout-dfg-eager-no-cjit jsc-layout-tests.yaml/js/script-tests/arguments-iterator.js.layout-ftl jsc-layout-tests.yaml/js/script-tests/arguments-iterator.js.layout-ftl-eager-no-cjit jsc-layout-tests.yaml/js/script-tests/arguments-iterator.js.layout-ftl-no-cjit jsc-layout-tests.yaml/js/script-tests/arguments-iterator.js.layout-no-cjit jsc-layout-tests.yaml/js/script-tests/arguments-iterator.js.layout-no-llint jsc-layout-tests.yaml/js/script-tests/arguments.js.layout jsc-layout-tests.yaml/js/script-tests/arguments.js.layout-dfg-eager-no-cjit jsc-layout-tests.yaml/js/script-tests/arguments.js.layout-ftl jsc-layout-tests.yaml/js/script-tests/arguments.js.layout-ftl-eager-no-cjit jsc-layout-tests.yaml/js/script-tests/arguments.js.layout-ftl-no-cjit jsc-layout-tests.yaml/js/script-tests/arguments.js.layout-no-cjit jsc-layout-tests.yaml/js/script-tests/arguments.js.layout-no-llint jsc-layout-tests.yaml/js/script-tests/basic-strict-mode.js.layout jsc-layout-tests.yaml/js/script-tests/basic-strict-mode.js.layout-dfg-eager-no-cjit jsc-layout-tests.yaml/js/script-tests/basic-strict-mode.js.layout-ftl jsc-layout-tests.yaml/js/script-tests/basic-strict-mode.js.layout-ftl-eager-no-cjit jsc-layout-tests.yaml/js/script-tests/basic-strict-mode.js.layout-ftl-no-cjit jsc-layout-tests.yaml/js/script-tests/basic-strict-mode.js.layout-no-cjit jsc-layout-tests.yaml/js/script-tests/basic-strict-mode.js.layout-no-llint jsc-layout-tests.yaml/js/script-tests/class-syntax-default-constructor.js.layout-no-llint jsc-layout-tests.yaml/js/script-tests/class-syntax-name.js.layout jsc-layout-tests.yaml/js/script-tests/class-syntax-name.js.layout-dfg-eager-no-cjit jsc-layout-tests.yaml/js/script-tests/class-syntax-name.js.layout-ftl jsc-layout-tests.yaml/js/script-tests/class-syntax-name.js.layout-ftl-eager-no-cjit jsc-layout-tests.yaml/js/script-tests/class-syntax-name.js.layout-ftl-no-cjit jsc-layout-tests.yaml/js/script-tests/class-syntax-name.js.layout-no-cjit jsc-layout-tests.yaml/js/script-tests/class-syntax-name.js.layout-no-llint jsc-layout-tests.yaml/js/script-tests/const.js.layout jsc-layout-tests.yaml/js/script-tests/const.js.layout-dfg-eager-no-cjit jsc-layout-tests.yaml/js/script-tests/const.js.layout-ftl jsc-layout-tests.yaml/js/script-tests/const.js.layout-ftl-eager-no-cjit jsc-layout-tests.yaml/js/script-tests/const.js.layout-ftl-no-cjit jsc-layout-tests.yaml/js/script-tests/const.js.layout-no-cjit jsc-layout-tests.yaml/js/script-tests/const.js.layout-no-llint jsc-layout-tests.yaml/js/script-tests/constant-count.js.layout jsc-layout-tests.yaml/js/script-tests/constant-count.js.layout-dfg-eager-no-cjit jsc-layout-tests.yaml/js/script-tests/constant-count.js.layout-ftl jsc-layout-tests.yaml/js/script-tests/constant-count.js.layout-ftl-eager-no-cjit jsc-layout-tests.yaml/js/script-tests/constant-count.js.layout-ftl-no-cjit jsc-layout-tests.yaml/js/script-tests/constant-count.js.layout-no-cjit jsc-layout-tests.yaml/js/script-tests/constant-count.js.layout-no-llint jsc-layout-tests.yaml/js/script-tests/dfg-inline-arguments-become-double.js.layout jsc-layout-tests.yaml/js/script-tests/dfg-inline-arguments-become-double.js.layout-dfg-eager-no-cjit jsc-layout-tests.yaml/js/script-tests/dfg-inline-arguments-become-double.js.layout-ftl jsc-layout-tests.yaml/js/script-tests/dfg-inline-arguments-become-double.js.layout-ftl-eager-no-cjit jsc-layout-tests.yaml/js/script-tests/dfg-inline-arguments-become-double.js.layout-ftl-no-cjit jsc-layout-tests.yaml/js/script-tests/dfg-inline-arguments-become-double.js.layout-no-cjit jsc-layout-tests.yaml/js/script-tests/dfg-inline-arguments-become-double.js.layout-no-llint jsc-layout-tests.yaml/js/script-tests/dfg-inline-arguments-become-int32.js.layout jsc-layout-tests.yaml/js/script-tests/dfg-inline-arguments-become-int32.js.layout-dfg-eager-no-cjit jsc-layout-tests.yaml/js/script-tests/dfg-inline-arguments-become-int32.js.layout-ftl jsc-layout-tests.yaml/js/script-tests/dfg-inline-arguments-become-int32.js.layout-ftl-eager-no-cjit jsc-layout-tests.yaml/js/script-tests/dfg-inline-arguments-become-int32.js.layout-ftl-no-cjit jsc-layout-tests.yaml/js/script-tests/dfg-inline-arguments-become-int32.js.layout-no-cjit jsc-layout-tests.yaml/js/script-tests/dfg-inline-arguments-become-int32.js.layout-no-llint jsc-layout-tests.yaml/js/script-tests/dfg-inline-arguments-reset-changetype.js.layout jsc-layout-tests.yaml/js/script-tests/dfg-inline-arguments-reset-changetype.js.layout-dfg-eager-no-cjit jsc-layout-tests.yaml/js/script-tests/dfg-inline-arguments-reset-changetype.js.layout-ftl jsc-layout-tests.yaml/js/script-tests/dfg-inline-arguments-reset-changetype.js.layout-ftl-eager-no-cjit jsc-layout-tests.yaml/js/script-tests/dfg-inline-arguments-reset-changetype.js.layout-ftl-no-cjit jsc-layout-tests.yaml/js/script-tests/dfg-inline-arguments-reset-changetype.js.layout-no-cjit jsc-layout-tests.yaml/js/script-tests/dfg-inline-arguments-reset-changetype.js.layout-no-llint jsc-layout-tests.yaml/js/script-tests/dfg-inline-arguments-reset.js.layout jsc-layout-tests.yaml/js/script-tests/dfg-inline-arguments-reset.js.layout-dfg-eager-no-cjit jsc-layout-tests.yaml/js/script-tests/dfg-inline-arguments-reset.js.layout-ftl jsc-layout-tests.yaml/js/script-tests/dfg-inline-arguments-reset.js.layout-ftl-eager-no-cjit jsc-layout-tests.yaml/js/script-tests/dfg-inline-arguments-reset.js.layout-ftl-no-cjit jsc-layout-tests.yaml/js/script-tests/dfg-inline-arguments-reset.js.layout-no-cjit jsc-layout-tests.yaml/js/script-tests/dfg-inline-arguments-reset.js.layout-no-llint jsc-layout-tests.yaml/js/script-tests/function-dot-arguments.js.layout jsc-layout-tests.yaml/js/script-tests/function-dot-arguments.js.layout-dfg-eager-no-cjit jsc-layout-tests.yaml/js/script-tests/function-dot-arguments.js.layout-ftl jsc-layout-tests.yaml/js/script-tests/function-dot-arguments.js.layout-ftl-eager-no-cjit jsc-layout-tests.yaml/js/script-tests/function-dot-arguments.js.layout-ftl-no-cjit jsc-layout-tests.yaml/js/script-tests/function-dot-arguments.js.layout-no-cjit jsc-layout-tests.yaml/js/script-tests/function-dot-arguments.js.layout-no-llint jsc-layout-tests.yaml/js/script-tests/named-function-expression.js.layout jsc-layout-tests.yaml/js/script-tests/named-function-expression.js.layout-dfg-eager-no-cjit jsc-layout-tests.yaml/js/script-tests/named-function-expression.js.layout-ftl jsc-layout-tests.yaml/js/script-tests/named-function-expression.js.layout-ftl-eager-no-cjit jsc-layout-tests.yaml/js/script-tests/named-function-expression.js.layout-ftl-no-cjit jsc-layout-tests.yaml/js/script-tests/named-function-expression.js.layout-no-cjit jsc-layout-tests.yaml/js/script-tests/named-function-expression.js.layout-no-llint regress/script-tests/deltablue-varargs.js.dfg-eager-no-cjit-validate regress/script-tests/deltablue-varargs.js.ftl-eager-no-cjit regress/script-tests/deltablue-varargs.js.ftl-no-cjit-validate regress/script-tests/deltablue-varargs.js.no-cjit-validate-phases Results for JSC stress tests: 89 failures found. I haven't investigated the rest of the failures yet, but at least the constant-count.js case is a regression.