RawPropsParser::at steps past every registered key to find a prop read out of order, though nameToIndex_ already maps it #59759

Description

Once a RawPropsParser is prepared, RawPropsParser::at looks at the key after the cursor and, when the key read is any other, steps the cursor one key at a time round every key the props struct registered, comparing each, until it reaches the one read. The parser already holds nameToIndex_, which maps every registered name to its index and which preparse searches for every raw prop, but at never uses it.

So a props struct that reads a key out of registration order pays one comparison per key between the cursor and that key, on every parse. The common case is a component's props that extend ViewProps and read one of View's keys again after the base constructor, width or backgroundColor for instance: the cursor sits on View's last key and walks round from the start to it. I met it in a component whose props read width, height and backgroundColor after ViewProps; each parse compared about a hundred extra keys.

The comment above the loop says to read props in the same order every time, but a subclass cannot read a base key without reading it out of order. Finding a key that is not at the cursor's next place through nameToIndex_.at(key) would make the read one lookup instead of a walk; I carry that change locally and it removes the walk.

Steps to reproduce

1. git clone https://github.com/YevheniiKotyrlo/react-native-fantom-reproducer && cd react-native-fantom-reproducer
2. ./fantom/reproduce.sh raw-props-out-of-order-read (needs Docker). It clones react/react-native at main, builds Fantom's tester as its CI does, and builds fantom/RawPropsOrder.cpp in the tester's CMake tree against the same libraries. fantom/raw-props-parser-compared-keys.patch adds two counters to RawPropsParser.cpp: the reads at answers once the parser is prepared, and the keys it compares their names with.
3. The program parses {width: 10, height: 10, tint: 1} as a component descriptor's cloneProps does (a parser prepared for the struct, RawProps::parse, then the struct's constructor) through three structs:

struct ViewOnlyProps : ViewProps { /* View's props and nothing more */ };

struct InOrderProps : ViewProps {
  InOrderProps(const PropsParserContext& context, const InOrderProps& sourceProps, const RawProps& rawProps)
      : ViewProps(context, sourceProps, rawProps),
        tint(convertRawProp(context, rawProps, "tint", sourceProps.tint, 0)) {}
  int tint{0};
};

struct OutOfOrderProps : ViewProps {
  OutOfOrderProps(const PropsParserContext& context, const OutOfOrderProps& sourceProps, const RawProps& rawProps)
      : ViewProps(context, sourceProps, rawProps),
        widthAgain(convertRawProp(context, rawProps, "width", sourceProps.widthAgain, 0.0f)) {}
  float widthAgain{0.0f};
};

Expected: reading width after ViewProps costs what reading tint costs, one read and one comparison more than View's props alone.

Seen: the width read costs 55 comparisons, the walk from the start of View's keys to width; a key View registers later costs more, up to every key View registers.

React Native Version

0.88.0 (reproduced on main at 11f37bd)

Affected Platforms

Other (please specify): ReactCommon, which every platform shares; reproduced on the cxx platform Fantom runs, on Linux

Areas

Fabric - The New Renderer

Output of npx @react-native-community/cli info

System:
  OS: Linux 6.18 Ubuntu 22.04.5 LTS 22.04.5 LTS (Jammy Jellyfish)
  CPU: (24) x64 AMD Ryzen 9 9950X3D 16-Core Processor
  Memory: 120.97 GB / 125.63 GB
  Shell:
    version: 5.1.16
    path: /bin/bash
Binaries:
  Node:
    version: 22.14.0
    path: /usr/local/bin/node
  Yarn:
    version: 1.22.22
    path: /usr/local/bin/yarn
  npm:
    version: 10.9.2
    path: /usr/local/bin/npm
  Watchman: Not Found
SDKs:
  Android SDK:
    API Levels:
      - "37"
    Build Tools:
      - 37.0.0
    Android NDK: 28.2.13676358
IDEs:
  Android Studio: Not Found
Languages:
  Java:
    version: 17.0.20.1
    path: /usr/bin/javac
  Ruby:
    version: 3.0.2
    path: /usr/bin/ruby
npmPackages:
  "@react-native-community/cli": Not Found
  react: Not Found
  react-native: Not Found
npmGlobalPackages:
  "*react-native*": Not Found
Android:
  hermesEnabled: Not found
  newArchEnabled: Not found
iOS:
  hermesEnabled: Not found
  newArchEnabled: Not found

Stacktrace or Logs

ViewOnlyProps    reads 222, keys compared 222
InOrderProps     reads 223, keys compared 223
InOrderProps     read tint 1
OutOfOrderProps  reads 223, keys compared 277
OutOfOrderProps  read width 10

MANDATORY Reproducer

https://github.com/YevheniiKotyrlo/react-native-fantom-reproducer

Screenshots and Videos

No response