What the React Compiler Quietly Skips

React Compiler 1.0 went stable in October 2025. Half the tutorials I saw declared useMemo dead. It's not — and on most existing codebases, the compiler will silently skip the components you most want it to optimize. The compiler handles one thing Re-render performance. It's a build-time plugin that analyzes your components and inserts memoization automatically, without you writing it. The genuinely useful part: it can memoize values in code paths after an early return, which manual useMemo can't do. function Component ({ isAdmin , data }) { if ( ! isAdmin ) return null ; const processed = expensiveTransformation ( data ); // compiler memoizes this return < Chart data = { processed } />; } What it doesn't touch: first render cost, Long Tasks from large list renders, expensive one-time computations on mount. None of that changes. Silent bailouts When the compiler encounters code it can't safely analyze — mutating props, reading mutable refs during render, class instances with internal st