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

[Stepan Dyatkovskiy]

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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