[llvm-commits] Reworked SwitchInst prototype with case-ranges.

[Stepan Dyatkovskiy]

ping.
Stepan Dyatkovskiy wrote:
> ping
> Stepan Dyatkovskiy wrote:
>> Hi all, please find the new SwitchInst prototype with case ranges in
>> attachment.
>>
>> Main features.
>>
>> 1. Ranges are stored in flat ordered numbers collection (thanks to
>> Duncan and Chandler for this idea). Range [Low, High) may be represented
>> as Low=collection[i], High=collection[i+1]. Thus all set of integers is
>> covered. The collection is terminated by the wrapped range:
>>    Low=collection[collection.size()-1], High=collection[0].
>> For each collection item we also assign BasicBlock, Range+BasicBlock
>> will called "Cluster". E.g.:
>>    [1 -> Default] [2 -> Successor0] [5 -> Successor1] [8 -> Successor2]
>>    That means that we have 3 clusters:
>>    [2, 5) -> Successor0
>>    [5, 8) -> Successor1
>>    [8, 1) -> Successor2 // This range is wrapped.
>>
>> 2. I introduced successor ID (SID).
>> We need associate successors with case-ranges. But both ranges and
>> successors collections may be changed asynchronously:
>>    Successors may change its indices during 'remove' operation.
>>    Ranges may be removed.
>> But we need to keep always actual successor information for each range.
>> Even if successor was replaced by optimizer or its index was changed.
>> That's why SID was introduced, it will the same always. In that case
>> several SIDs may be assigned to the same successor after optimization.
>>
>> 3. Ranges directed to the default successor are always skipped during
>> iteration. Thus when user invokes getNumRanges, he got number of
>> non-default ranges. When user gets iterator case_begin(), he got
>> iterator to the first non-default range. And so on.
>> Probably its is less generic way. But it helps to reduce ranges
>> processing time. Since we process default after all, as some kind of
>> remainder.
>>
>> 4. Support for clusterification. Iterator has method
>> getClusterAndGoNext. This method allows to iterate over merged ranges
>> with the same successor and neighbouring borders. So if you need to
>> collect optimized clusters you just should use
>> CaseIt::getClusterAndGoNext instead of standard ++ operation.
>>
>> P.S.: IntegersSubset, IntegersSubsetMapping and IntegersSubsetTest will
>> go away. I excluded these changes from current patch for better and
>> cleaner looking.
>>
>> Thanks,
>> -Stepan.
>