[LLVMdev] Question about IndVarSimplify

[Sorin Baltateanu]

Thanks. Works fine now and made some other things clear too.

On Sun, Jun 19, 2011 at 9:22 PM, Eli Friedman <eli.friedman at gmail.com>wrote:

> On Sun, Jun 19, 2011 at 7:21 AM, Sorin Baltateanu
> <baltateanu.sorin at gmail.com> wrote:
> > Hi guys,
> >
> > I am trying to use the indvars pass, but i don't see any changes in the
> IL
> > representation.
> >
> > For this simple function
> >
> > void init_array(int k)
> > {
> >     int A[20];
> >     for (int i=2; i<10; i++)
> >         A[i] = 0;
> > }
> >
> > i run clang test-simple.c -S -emit-llvm -o test.il and i obtain the
> > following il representation
> >
> > define void @init_array(i32 %k) nounwind {
> > entry:
> >   %k.addr = alloca i32, align 4
> >   %A = alloca [20 x i32], align 4
> >   %i = alloca i32, align 4
> >   store i32 %k, i32* %k.addr, align 4
> >   store i32 2, i32* %i, align 4
> >   br label %for.cond
> >
> > for.cond:                                         ; preds = %for.inc,
> %entry
> >   %tmp = load i32* %i, align 4
> >   %cmp = icmp slt i32 %tmp, 10
> >   br i1 %cmp, label %for.body, label %for.end
> >
> > for.body:                                         ; preds = %for.cond
> >   %tmp1 = load i32* %i, align 4
> >   %arrayidx = getelementptr inbounds [20 x i32]* %A, i32 0, i32 %tmp1
> >   store i32 0, i32* %arrayidx, align 4
> >   br label %for.inc
> >
> > for.inc:                                          ; preds = %for.body
> >   %tmp2 = load i32* %i, align 4
> >   %inc = add nsw i32 %tmp2, 1
> >   store i32 %inc, i32* %i, align 4
> >   br label %for.cond
> >
> > for.end:                                          ; preds = %for.cond
> >   ret void
> > }
> >
> > Running opt -loop-simplify < test.il -S gives me the same output, which
> is
> > what i would expect.
> > The problem is that running opt -indvars < test.il -S gives, again, the
> same
> > output, but i would expect that i starts from 0 and is, eventualy,
> defined
> > using a PHYNode.
> >
> > What it's wrong with what i'm doing?
>
> You aren't running a normal pass pipeline; in particular, not running
> mem2reg/scalarrepl first prevents a lot of optimizations from working
> as expected.
>
> -Eli
>
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