[llvm-commits] New classes for PR1255: Should enhance LLVM switch instruction to take case ranges.
Stepan Dyatkovskiy
STPWORLD at narod.ru
Fri Apr 27 12:37:47 PDT 2012
ping.
25.04.2012, 23:09, "Stepan Dyatkovskiy" <STPWORLD at narod.ru>:
> Hi Chris. I commited new classes in r155464. I want to realize points summarized here:
> http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20120305/138780.html
>
> And more generally I propose to start very-very carefully (watch for buildbots, take in account all remarks and so on) go within this way:
>
> 0. Implement new classes. Classes doesn't affect anything. They still work with ConstantInt base values at this stage.
> 1. Fictitious replacement of current ConstantInt case values with ConstantRangesSet. Case ranges set will still hold single value, and ConstantInt *getCaseValue() will return it. But additionally implement new method in SwitchInst that allows to work with case ranges. Currenly I think it should be some wrapper that returns either single value or ConstantRangesSet object.
> 2. Step-by-step replacement of old "ConstantInt* getCaseValue()" with new alternative. Modify algorithms for all passes that works with SwitchInst. But don't modify LLParser and BitcodeReader/Writer. Still hold single value in each ConstantRangesSet object. On this stage some parts of LLVM will use old-style methods, and some ones new-style.
> 3. After all getCaseValue() usages will removed and whole LLVM and its clients will work in new style - modify LLParser, Reader and Writer. Remove getCaseValue().
> 4. Replace ConstantInt*-based case ranges set items with APInt ones.
>
> Can you give me your approval for that?
> Thanks.
>
> -Stepan.
>
> 26.03.2012, 18:26, "Stepan Dyatkovskiy" <STPWORLD at narod.ru>:
>
>> 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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