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LibJS: Give VM a cache of single-ASCII-character PrimitiveString

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A large number of JS strings are a single ASCII character. This patch
adds a 128-entry cache for those strings to the VM. The cost of the
cache is 1536 byte of GC heap (all in same block) + 2304 bytes malloc.

This avoids a lot of GC heap allocations, and packing all of these
in the same heap block is nice for fragmentation as well.
This commit is contained in:
Andreas Kling 2020-10-22 17:43:48 +02:00
parent 5c2520e6b2
commit 619cd613d0
3 changed files with 17 additions and 0 deletions
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6
Libraries/LibJS/Runtime/VM.h
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@ -108,6 +108,11 @@ public:
Symbol* get_global_symbol(const String& description);
PrimitiveString& empty_string() { return *m_empty_string; }
PrimitiveString& single_ascii_character_string(u8 character)
{
ASSERT(character < 0x80);
return *m_single_ascii_character_strings[character];
}
CallFrame& push_call_frame(bool strict_mode = false)
{
@ -247,6 +252,7 @@ private:
HashMap<String, Symbol*> m_global_symbol_map;
PrimitiveString* m_empty_string { nullptr };
PrimitiveString* m_single_ascii_character_strings[128] {};
#define __JS_ENUMERATE(SymbolName, snake_name) \
Symbol* m_well_known_symbol_##snake_name { nullptr };