[llvm-dev] ind variable

[Anastasiya Ruzhanskaya via llvm-dev]

...or maybe the second operand of ICmp

2017-08-09 14:51 GMT+02:00 Anastasiya Ruzhanskaya <
anastasiya.ruzhanskaya at frtk.ru>:

> SCEV , seems to me that this is a little disadvantage ( I am not an expert
> by now in llvm, but think so), does not keep a cmp instruction, where
> someone can find a value , with which an induction variable is compared.
> When it is impossible to determine a trip count, that information can be
> useful ( hope not only for me). Still after receiving a block where this
> instruction is, it is not really hard to find the ICmp, but still...
>
> 2017-08-09 14:28 GMT+02:00 Tobias Grosser <tobias.grosser at inf.ethz.ch>:
>
>> This support was removed years ago from indvars. We don't need canonical
>> induction variables any more as all analysis are done on SCEVs. The SCEV
>> generator can transform them even without the need for explicit
>> canonical induction variables.
>>
>> Best,
>> Tobias
>>
>> On Wed, Aug 9, 2017, at 14:23, Anastasiya Ruzhanskaya via llvm-dev
>> wrote:
>> > The files of this strange pass are described here
>> > http://reviews.legup.org/rLEGUP54ca7c2bb15d84116baf47bce67256d3803720d9
>> > .
>> > I wonderwhy the most uptodate -indvars pass can't do the same.
>> >
>> > 2017-08-09 14:18 GMT+02:00 Anastasiya Ruzhanskaya <
>> > anastasiya.ruzhanskaya at frtk.ru>:
>> >
>> > > Hello,
>> > > I have this piece of code:
>> > > int main() {
>> > >         int m = 0;
>> > > //      int i, j, k;
>> > > //      int N = f()%10;
>> > >         for (int l = 0; l < 1000; l+=4)
>> > >                 printf("%d", l);
>> > >
>> > > I am sure, that llvm is capable to convert this into canonical
>> induction
>> > > variable, but even with O3
>> > > define i32 @main() #0 {
>> > >   br label %2
>> > >
>> > > ; <label>:1                                       ; preds = %2
>> > >   ret i32 0
>> > >
>> > > ; <label>:2                                       ; preds = %0, %2
>> > >   %l.01 = phi i32 [ 0, %0 ], [ %4, %2 ]
>> > >   %3 = tail call i32 (i8*, ...) @printf(i8* nonnull getelementptr
>> inbounds
>> > > ([3 x i8], [3 x i8]* @.str, i64 0, i64 0), i32 %l.01)
>> > >   %4 = add nuw nsw i32 %l.01, 4
>> > >   %5 = icmp slt i32 %4, 1000
>> > >   br i1 %5, label %2, label %1
>> > > }
>> > >
>> > > I have this assembler.
>> > > I know there is indvars2 pass ( it is under llvm license but used
>> only in
>> > > LegUp project - as I understood, surfing the Internet), which is good
>> in
>> > > changing induction variables.
>> > >
>> > > How can I achieve that this cycle will have a canonical indvar?
>> > >
>> > _______________________________________________
>> > LLVM Developers mailing list
>> > llvm-dev at lists.llvm.org
>> > http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>
>
>
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