Inline small strings in JSString::m_fiber - #307

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robobun wants to merge 69 commits into

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bun-inline-small-strings

Commits on Jul 19, 2026

WIP: inline small strings (runtime + LLInt + baseline JIT correct)
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DFG/FTL: guard rope-layout reads against inline small strings
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JIT: handle inline small strings on rope-taken branches (DFG/FTL)
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DFG: don't constant-fold ResolveRope through inline small strings
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JSStringInlines: handle inline small-string fibers in resolveToBuffer
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LLInt/runtime: handle inline small-string fibers in op_switch_char and tryGetValueWithoutGC
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Phase 2: JIT fast paths for inline small strings
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FTL stringsEqual: inline-vs-inline m_fiber compare
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Add SpecStringInline speculation and literal-vs-inline equality fast path
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FTL: isLikelyInlineString helper + speculative inline length path
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Speculative inline charCodeAt (DFG+FTL) and short-concat inlining
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JSString::view(): materialize inline strings before returning a StringView
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Use 3-bit inlineLengthMask (0x7) instead of 0x1f
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view() returns in-cell StringView again; fix JSStringJoiner instead
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DFG/FTL MakeRope: route short all-8-bit concats to the inline creator
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JSBigInlineString: 24-byte inline cell for 8..15 Latin-1 / 4..7 UTF-16 chars
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JSStringBuilder: stack-buffered builder emitting inline JSString cells
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Inline small strings: eliminate materialization hotspots + 32-byte big-inline + fiber-word cache
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Revert JSBigInlineString to 24 bytes; width-aware equality bail
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FTL MakeRope: allocate the rope cell after inline-child/short-result bails
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InlinePropertyKey.h: tagged-uid shim layer (scaffold for change set 6)
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CacheableIdentifier: accept 16-byte inline JSStrings as cacheable ByVal keys
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CacheableIdentifier: make inline JSStrings cacheable ByVal keys (atom-resolve variant)
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Identifier.h: guard include + uidHash/parseIndex shims (BUN_JSC_ADDITIONS)
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StructureInlines.h: guarded InlinePropertyKey include + uidHash shims
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HasOwnPropertyCache: guard hash() with InlinePropertyKey shim
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StructureTransitionTable.h: inline-key include, ASSERT relax, static_assert
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MegamorphicCache.h: guarded InlinePropertyKey include + uidHash shims
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PropertyTable: InlinePropertyKey shims for ASSERT/ref/deref
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InlinePropertyKey phase A: tag-aware deref shims at the hash/isSymbol/ref/deref chokepoints
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MegamorphicCache: keep uid->hash() on non-fiber path for JIT sync
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Phase 3 (partial): view() instead of value() in replaceAll-cache and tryReplaceOneChar
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InlinePropertyKey shims: [[unlikely]] on the fiber-word branch
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InlinePropertyKey phase 3: remaining value()->view() swaps
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InlinePropertyKey phase D.1+D.2: Identifier tagged uintptr_t storage + fiber-word producer
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InlinePropertyKey phase D.5: deref guards at impl() sites hit after the producer
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InlinePropertyKey phase D.6: RefPtr<UniquedStringImpl> fields fiber-aware
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InlinePropertyKey phase C: JIT tag branches at StringImpl::m_hashAndFlags load sites
robobun
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Commits on Jul 20, 2026

Commits on Jul 21, 2026