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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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7
Libraries/LibJS/Runtime/VM.cpp
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@ -47,6 +47,10 @@ VM::VM()
: m_heap(*this)
{
m_empty_string = m_heap.allocate_without_global_object<PrimitiveString>(String::empty());
for (size_t i = 0; i < 128; ++i) {
m_single_ascii_character_strings[i] = m_heap.allocate_without_global_object<PrimitiveString>(String::format("%c", i));
}
#define __JS_ENUMERATE(SymbolName, snake_name) \
m_well_known_symbol_##snake_name = js_symbol(*this, "Symbol." #SymbolName, false);
JS_ENUMERATE_WELL_KNOWN_SYMBOLS
@ -96,6 +100,9 @@ VM::InterpreterExecutionScope::~InterpreterExecutionScope()
void VM::gather_roots(HashTable<Cell*>& roots)
{
roots.set(m_empty_string);
for (auto* string : m_single_ascii_character_strings)
roots.set(string);
if (m_exception)
roots.set(m_exception);