[llvm-commits] New classes for PR1255: Should enhance LLVM switch instruction to take case ranges.

[Stepan Dyatkovskiy]

Hi Chris. Proceed discussion? ;-)
-Stepan.

Stepan Dyatkovskiy wrote:
> ping
>
> 23.03.2012, 16:40, "Stepan Dyatkovskiy"<stpworld at narod.ru>:
>> Hi Chris.
>>
>> // Some range class it may be ConstantRange as Duncan proposed.
>> class Range {
>>     APInt Low;
>>     APInt High;
>>
>>     public:
>>
>>     // Some interface here (getLow, getHigh,<,>, isInRange and so on).
>> }
>>
>> class ConstantRangesSet {
>>     std::vector<Range>  Ranges;
>>
>>     /// Checks is the given constant satisfies this case.
>>     bool isSatisfies(const APInt&  N);
>>
>>     /// Returns number of ranges.
>>     unsigned getNumItems() const;
>>
>>     /// Returns set item with given index.
>>     const Range&  getItem(unsigned idx);
>> }
>>
>> SingleNumber is APInt instead.
>>
>> -Stepan.
>>
>> Chris Lattner wrote:
>>
>>>   On Mar 11, 2012, at 1:00 AM, Stepan Dyatkovskiy wrote:
>>>>   Hi Chris.
>>>>
>>>>   Summary of previous discussion:
>>>>   1. Finally ConstantInt should be replaced with APInt.
>>>>   2. How to store case ranges. I remind your last proposal:
>>>>
>>>>   [quote]
>>>>
>>>>   The mapping of the range to entries in CaseValues could look like this:
>>>>
>>>>   [N, N+1] ->    Single element in CaseValues indicates the case value for the destination.
>>>>   [MAXINT, MININT] ->    The entire case is "default"
>>>>   Otherwise, the pair indicates a series of ranges (inclusive).  If one of the ranges is MAXINT/MININT, then it is the default case.  For example [0, 4, 6,6]  would handle 0,1,2,3,4,6.  [4,6, MAXINT,MININT] would handle 4,5,6 and default.
>>>>
>>>>   [/quote]
>>>>
>>>>   My proposal was to create ConstantRangesSet that will store all numbers and ranges for complex case. I still propose to use this schema.
>>>>   You can ask what about most probable case, when for most of successors will be the only case value?
>>>>   OK. We can create collection for "classic" cases  vector<pair<SingleNumber,Success>    >    too. Then finally on the top level we have 2 collections:
>>>>   class SwitchInst {
>>>>   ..
>>>>     vector<pair<SingleNumber, BasicBlock*>    >    ClassicCases;
>>>>     vector<pair<ConstantRangesSet, BasicBlock>    >    ComplexCases;
>>>>   ..
>>>>   }
>>>>
>>>>   So, what do you think about this?
>>>   This approach seems sensible to me.  Can you sketch out what SingleNumber and ConstantRangesSet look like?
>>>
>>>   -Chris
>>
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