591161 - JM: Return from Stub Call in Register on x64

Status: RESOLVED WONTFIX

(Core :: JavaScript Engine, defect)

Description

[Sean Stangl [:sstangl]]

Most stub calls return Values by writing them to memory, from which they are immediately read. This is very slow. On x64, since the register size is sizeof(Value), we can just store the return value directly in a register. Stores are intensive, so the savings should be worthwhile.

This is highly non-trivial to do well, as it requires changing the register allocator to understand that VALUE is a valid RematType. The assumption that TYPE and DATA are the only available RematTypes is all over the codebase.

Comment 1

[Luke Wagner [:luke]]

JM was removed.