Avoid cloneStr for small strings and intern tokenizer identifiers

[Zaczero]

By avoiding cloneStr overhead on small strings we recover about 6% of the performance at no peak rss change. Strings shorter than 13 are never SlicedString and they don't hold a reference to the parent memory:

if (!v8_flags.string_slices || length < SlicedString::kMinLength) return NewCopiedSubstring(...)

measurement          mean ± σ            min … max           outliers         delta
wall_time          14.9s  ±  400ms                              14.2s  … 15.6s                                     0 ( 0%)        ⚡-  6.0% ±  1.4%
peak_rss           2.66GB ± 7.72MB                              2.64GB … 2.67GB                                    1 ( 6%)          +  0.2% ±  0.2%
cpu_cycles          121G  ± 2.75G                                116G  …  125G                                     0 ( 0%)        ⚡-  4.1% ±  1.2%
instructions        198G  ±  193M                                198G  …  198G                                     2 (12%)        ⚡-  1.7% ±  0.1%
cache_references   8.67G  ± 41.2M                               8.57G  … 8.73G                                     0 ( 0%)        ⚡-  4.5% ±  0.4%
cache_misses       2.04G  ± 18.9M                               2.00G  … 2.07G                                     0 ( 0%)          -  1.3% ±  0.6%
branch_misses       734M  ± 3.59M                                728M  …  740M                                     0 ( 0%)          -  0.9% ±  0.4%

By further interning identifier strings we get in total 10% performance gain and reduce peak memory usage by about 1%. Tested on the openstreetmap-ng codebase.

measurement          mean ± σ            min … max           outliers         delta
wall_time          14.2s  ±  395ms                              13.6s  … 14.7s                                     0 ( 0%)        ⚡- 10.7% ±  1.4%
peak_rss           2.63GB ± 2.89MB                              2.62GB … 2.63GB                                    0 ( 0%)          -  0.9% ±  0.1%
cpu_cycles          106G  ± 2.55G                                102G  …  111G                                     0 ( 0%)        ⚡- 15.8% ±  1.1%
instructions        177G  ±  305M                                177G  …  178G                                     1 ( 6%)        ⚡- 11.9% ±  0.1%
cache_references   8.26G  ± 46.0M                               8.15G  … 8.34G                                     1 ( 6%)        ⚡-  9.0% ±  0.4%
cache_misses       1.96G  ± 19.8M                               1.93G  … 2.00G                                     2 (12%)        ⚡-  5.1% ±  0.6%
branch_misses       687M  ± 4.15M                                680M  …  694M                                     0 ( 0%)        ⚡-  7.3% ±  0.4%

This improves the runtime performance while preserving the memory reduction of cloneStr.

Personal note: I find it surprising that #9993 did not mention (or measure) performance regressions at all. Especially since in memory-constrained environments you can opt out of the SlicedString by compiling with --no-string-slices.

[rchiodo]

Seems good to me. @heejaechang any thoughts?

[github-actions]

Diff from mypy_primer, showing the effect of this PR on open source code:

sympy (https://github.com/sympy/sympy)
+   .../projects/sympy/sympy/solvers/diophantine/diophantine.py:173:44 - error: Cannot access attribute "expand" for class "Basic"
+     Attribute "expand" is unknown (reportAttributeAccessIssue)
-   .../projects/sympy/sympy/solvers/diophantine/diophantine.py:528:23 - error: Operator "+" not supported for types "Generator[Unknown | int, Unknown, None] | list[Unknown | int]" and "list[Unknown | int]"
+   .../projects/sympy/sympy/solvers/diophantine/diophantine.py:528:23 - error: Operator "+" not supported for types "Generator[Unknown | Literal[1], Unknown, None] | list[Unknown | Literal[1]]" and "list[Unknown | int]"
-     Operator "+" not supported for types "Generator[Unknown | int, Unknown, None]" and "list[Unknown | int]" (reportOperatorIssue)
+     Operator "+" not supported for types "Generator[Unknown | Literal[1], Unknown, None]" and "list[Unknown | int]" (reportOperatorIssue)
+   .../projects/sympy/sympy/solvers/diophantine/tests/test_diophantine.py:313:30 - error: Cannot access attribute "as_independent" for class "Basic"
+     Attribute "as_independent" is unknown (reportAttributeAccessIssue)
+   .../projects/sympy/sympy/solvers/diophantine/tests/test_diophantine.py:382:30 - error: Cannot access attribute "as_independent" for class "Basic"
+     Attribute "as_independent" is unknown (reportAttributeAccessIssue)
+   .../projects/sympy/sympy/solvers/ode/hypergeometric.py:246:67 - error: Operator "**" not supported for types "Basic" and "Literal[2]" (reportOperatorIssue)
-   .../projects/sympy/sympy/solvers/ode/lie_group.py:618:61 - error: Operator "-" not supported for type "Unknown | Basic" (reportOperatorIssue)
-   .../projects/sympy/sympy/solvers/ode/nonhomogeneous.py:467:28 - error: Argument of type "Unknown | None" cannot be assigned to parameter "expr" of type "Expr" in function "make_args"
+   .../projects/sympy/sympy/solvers/ode/nonhomogeneous.py:467:28 - error: Argument of type "Expr | Unknown | None" cannot be assigned to parameter "expr" of type "Expr" in function "make_args"
-     Type "Unknown | None" is not assignable to type "Expr"
+     Type "Expr | Unknown | None" is not assignable to type "Expr"
+   .../projects/sympy/sympy/solvers/ode/ode.py:1515:38 - error: Object of type "None" is not subscriptable (reportOptionalSubscript)
+   .../projects/sympy/sympy/solvers/ode/ode.py:1516:38 - error: Object of type "None" is not subscriptable (reportOptionalSubscript)
+   .../projects/sympy/sympy/solvers/ode/ode.py:1526:9 - error: No overloads for "update" match the provided arguments (reportCallIssue)
+   .../projects/sympy/sympy/solvers/ode/ode.py:1526:12 - error: "update" is not a known attribute of "None" (reportOptionalMemberAccess)
+   .../projects/sympy/sympy/solvers/ode/ode.py:1526:19 - error: Argument of type "Unknown | dict[Unknown, Unknown] | None" cannot be assigned to parameter "m" of type "Iterable[tuple[str, Unknown]]" in function "update"
+     Type "Unknown | dict[Unknown, Unknown] | None" is not assignable to type "Iterable[tuple[str, Unknown]]"
+       "None" is incompatible with protocol "Iterable[tuple[str, Unknown]]"
+         "__iter__" is not present (reportArgumentType)
+   .../projects/sympy/sympy/solvers/ode/ode.py:1533:43 - error: Object of type "None" is not subscriptable (reportOptionalSubscript)
+   .../projects/sympy/sympy/solvers/ode/ode.py:1533:64 - error: Object of type "None" is not subscriptable (reportOptionalSubscript)
+   .../projects/sympy/sympy/solvers/ode/ode.py:1539:9 - error: No overloads for "update" match the provided arguments (reportCallIssue)
+   .../projects/sympy/sympy/solvers/ode/ode.py:1539:12 - error: "update" is not a known attribute of "None" (reportOptionalMemberAccess)
+   .../projects/sympy/sympy/solvers/ode/ode.py:1539:19 - error: Argument of type "Unknown | dict[Unknown, Unknown] | None" cannot be assigned to parameter "m" of type "Iterable[tuple[str, Unknown]]" in function "update"
+     Type "Unknown | dict[Unknown, Unknown] | None" is not assignable to type "Iterable[tuple[str, Unknown]]"
+       "None" is incompatible with protocol "Iterable[tuple[str, Unknown]]"
+         "__iter__" is not present (reportArgumentType)
+   .../projects/sympy/sympy/solvers/ode/ode.py:1546:43 - error: Object of type "None" is not subscriptable (reportOptionalSubscript)
+   .../projects/sympy/sympy/solvers/ode/ode.py:1546:74 - error: Object of type "None" is not subscriptable (reportOptionalSubscript)
+   .../projects/sympy/sympy/solvers/ode/ode.py:1552:9 - error: No overloads for "update" match the provided arguments (reportCallIssue)
+   .../projects/sympy/sympy/solvers/ode/ode.py:1552:12 - error: "update" is not a known attribute of "None" (reportOptionalMemberAccess)
+   .../projects/sympy/sympy/solvers/ode/ode.py:1552:19 - error: Argument of type "Unknown | dict[Unknown, Unknown] | None" cannot be assigned to parameter "m" of type "Iterable[tuple[str, Unknown]]" in function "update"
+     Type "Unknown | dict[Unknown, Unknown] | None" is not assignable to type "Iterable[tuple[str, Unknown]]"
+       "None" is incompatible with protocol "Iterable[tuple[str, Unknown]]"
+         "__iter__" is not present (reportArgumentType)
+   .../projects/sympy/sympy/solvers/ode/ode.py:1559:49 - error: Object of type "None" is not subscriptable (reportOptionalSubscript)
+   .../projects/sympy/sympy/solvers/ode/ode.py:1559:70 - error: Object of type "None" is not subscriptable (reportOptionalSubscript)
-   .../projects/sympy/sympy/solvers/ode/ode.py:1689:36 - error: Cannot access attribute "lhs" for class "Expr"
-     Attribute "lhs" is unknown (reportAttributeAccessIssue)
-   .../projects/sympy/sympy/solvers/ode/ode.py:1689:55 - error: Cannot access attribute "rhs" for class "Expr"
-     Attribute "rhs" is unknown (reportAttributeAccessIssue)
-   .../projects/sympy/sympy/solvers/ode/ode.py:1690:36 - error: Cannot access attribute "lhs" for class "Expr"
-     Attribute "lhs" is unknown (reportAttributeAccessIssue)
-   .../projects/sympy/sympy/solvers/ode/ode.py:1691:17 - error: No overloads for "__setitem__" match the provided arguments (reportCallIssue)
-   .../projects/sympy/sympy/solvers/ode/ode.py:1691:17 - error: Argument of type "Equality | BooleanFalse | BooleanTrue | Unknown | Expr" cannot be assigned to parameter "value" of type "Equality | BooleanFalse | BooleanTrue" in function "__setitem__"
-     Type "Equality | BooleanFalse | BooleanTrue | Unknown | Expr" is not assignable to type "Equality | BooleanFalse | BooleanTrue"
-       Type "Expr" is not assignable to type "Equality | BooleanFalse | BooleanTrue"
-         "Expr" is not assignable to "Equality"
-         "Expr" is not assignable to "BooleanFalse"
-         "Expr" is not assignable to "BooleanTrue" (reportArgumentType)
+   .../projects/sympy/sympy/solvers/ode/ode.py:3378:7 - error: "update" is not a known attribute of "None" (reportOptionalMemberAccess)
+   .../projects/sympy/sympy/solvers/ode/ode.py:3378:38 - error: Object of type "None" is not subscriptable (reportOptionalSubscript)
+   .../projects/sympy/sympy/solvers/ode/ode.py:3379:7 - error: "update" is not a known attribute of "None" (reportOptionalMemberAccess)
+   .../projects/sympy/sympy/solvers/ode/ode.py:3379:38 - error: Object of type "None" is not subscriptable (reportOptionalSubscript)
+   .../projects/sympy/sympy/solvers/ode/ode.py:3380:14 - error: Object of type "None" is not subscriptable (reportOptionalSubscript)
+   .../projects/sympy/sympy/solvers/ode/ode.py:3381:14 - error: Object of type "None" is not subscriptable (reportOptionalSubscript)
+   .../projects/sympy/sympy/solvers/ode/ode.py:3382:14 - error: Object of type "None" is not subscriptable (reportOptionalSubscript)
+   .../projects/sympy/sympy/solvers/ode/ode.py:3394:50 - error: Object of type "None" is not subscriptable (reportOptionalSubscript)
+   .../projects/sympy/sympy/solvers/ode/ode.py:3395:50 - error: Object of type "None" is not subscriptable (reportOptionalSubscript)
+   .../projects/sympy/sympy/solvers/ode/ode.py:3396:50 - error: Object of type "None" is not subscriptable (reportOptionalSubscript)
+   .../projects/sympy/sympy/solvers/ode/ode.py:3436:5 - error: No overloads for "update" match the provided arguments (reportCallIssue)
+   .../projects/sympy/sympy/solvers/ode/ode.py:3436:7 - error: "update" is not a known attribute of "None" (reportOptionalMemberAccess)
+   .../projects/sympy/sympy/solvers/ode/ode.py:3436:14 - error: Argument of type "Unknown | dict[Unknown, Unknown] | None" cannot be assigned to parameter "m" of type "Iterable[tuple[str, Unknown]]" in function "update"
+     Type "Unknown | dict[Unknown, Unknown] | None" is not assignable to type "Iterable[tuple[str, Unknown]]"
+       "None" is incompatible with protocol "Iterable[tuple[str, Unknown]]"
+         "__iter__" is not present (reportArgumentType)
+   .../projects/sympy/sympy/solvers/ode/ode.py:3437:18 - error: Object of type "None" is not subscriptable (reportOptionalSubscript)
+   .../projects/sympy/sympy/solvers/ode/ode.py:3437:43 - error: Object of type "None" is not subscriptable (reportOptionalSubscript)
+   .../projects/sympy/sympy/solvers/ode/ode.py:3438:9 - error: Object of type "None" is not subscriptable (reportOptionalSubscript)
+   .../projects/sympy/sympy/solvers/ode/ode.py:3438:16 - error: Object of type "None" is not subscriptable (reportOptionalSubscript)
+   .../projects/sympy/sympy/solvers/ode/ode.py:3438:24 - error: Object of type "None" is not subscriptable (reportOptionalSubscript)
+   .../projects/sympy/sympy/solvers/ode/ode.py:3438:31 - error: Object of type "None" is not subscriptable (reportOptionalSubscript)
+   .../projects/sympy/sympy/solvers/ode/ode.py:3439:9 - error: Object of type "None" is not subscriptable (reportOptionalSubscript)
+   .../projects/sympy/sympy/solvers/ode/ode.py:3439:15 - error: Object of type "None" is not subscriptable (reportOptionalSubscript)

... (truncated 302 lines) ...