[webkit-dev] Unnecessary instructions in bytecode
oliver at apple.com
Fri May 23 05:05:57 PDT 2008
Without actually know which instructions you think are unnecessary
this is difficult to answer, but i'll see if i can guess which you're
> 9 instructions; 224 bytes at 0x69ca30; 2 locals (0 parameters); 2
> [ 0] load lr6, undefined(@k0)
> [ 3] load lr7, undefined(@k0)
Technically we should be able to determine which of these loads are
actually necessary (eg. neither of them), but we currently don't
perform any data flow analysis so can't.
> [ 6] load tr0, undefined(@k0)
> [ 12] mov tr0, lr6
> [ 23] mov tr0, lr7
> [ 26] end tr0
These repeated moves into tr0 are to handle the implied return value
of global (and eval) code. Once again we should be able to remove
these, but currently do not perform enough analysis to work that out
> These instructions are unnecessary, aren't they?
> Or is there a technical explanation of them?
Not all of them are necessary, it's just easier for global/eval code
to be less efficient at the moment -- with sufficient work we could
get rid of the redundant stores, but currently there are other much
lower hanging fruit to work on (there are still optimisations that we
had added to the ast interpreter that aren't in squirrelfish) :D
Hope this helps,
> webkit-dev mailing list
> webkit-dev at lists.webkit.org
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