[llvm-dev] ind variable

[Anastasiya Ruzhanskaya via llvm-dev]

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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