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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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4
Libraries/LibJS/Runtime/PrimitiveString.cpp
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@ -42,6 +42,10 @@ PrimitiveString* js_string(Heap& heap, String string)
{
if (string.is_empty())
return &heap.vm().empty_string();
if (string.length() == 1 && (u8)string.characters()[0] < 0x80)
return &heap.vm().single_ascii_character_string(string.characters()[0]);
return heap.allocate_without_global_object<PrimitiveString>(move(string));
}