[Webkit-unassigned] [Bug 104638] Support op_switch_imm bytecode on DFG.

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=104638


Filip Pizlo <fpizlo at apple.com> changed:

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--- Comment #2 from Filip Pizlo <fpizlo at apple.com>  2012-12-11 01:26:56 PST ---
(From update of attachment 178731)
I don't think this is the right approach.  For large switch statements, this will perform worse.  I also fear that your way of creating multiple basic blocks is fragile - I can't see any obvious bugs in it, but it's kind of a dangerous approach that requires a mutable context to be held in place while you repeatedly revisit the same bytecode.  A better way of handling Switch in an optimizing compiler is to (a) have a Switch node in the DFG IR and (b) perform transformations on the Switch later in compilation if you find that it's a trivial one.  Writing a phase to handle (b) would give you the ability to have a more straight-forward handling of basic block creation.  Using (a) and allowing the Switch to sometimes survive into the backend (particularly when it's a Switch with a lot of cases) would take care of pathologies for large switch statements.

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