[llvm-dev] ind variable

[Tobias Grosser via llvm-dev]

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?
> >
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