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

[Stepan Dyatkovskiy]

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.
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