[LLVMdev] Switch instruction lowering

Anton Korobeynikov anton at korobeynikov.info
Wed Oct 29 09:11:38 PDT 2014


Some of the early ideas were actually described in
http://llvm.org/pubs/2007-05-31-Switch-Lowering.pdf

On Wed, Oct 29, 2014 at 3:52 AM, Hans Wennborg <hans at chromium.org> wrote:
> On Mon, Oct 27, 2014 at 2:54 AM, PaweĊ‚ Bylica <chfast at gmail.com> wrote:
>> Hi,
>>
>> I'm interested in any information about implementations of switch
>> instruction and its runtime cost. If it's very target dependent, I'm mostly
>> care about X86. Pointing some LLVM code is also good.
>
> I don't think there's any documentation besides the comments in the
> code, but switch lowering (to binary tree or jump table, etc.) happens
> in SelectionDAGBuilder::visitSwitch()
>
> For switches which are used to select from a set of constant values,
> SimplifyCFG will attempt to build a lookup table.
>
>  - Hans
>
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-- 
With best regards, Anton Korobeynikov
Faculty of Mathematics and Mechanics, Saint Petersburg State University




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