Patch for misleading comment in src/share/vm/opto/node.cpp

[Christian Thalinger]

On Mon, 2009-02-23 at 11:15 -0800, Peter B. Kessler wrote:
> Peter B. Kessler wrote:
> > This comment is so wrong as almost to qualify as malicious.  Here's a 
> > patch that might help.
> > 
> >      src/share/vm/opto/node.cpp
> > 
> >      971 // If you modify the 'this' pointer's inputs, you must use 'set_req' with
> >      972 // def-use info.  If you are making a new Node (either as the new root or
> >      973 // some new internal piece) you must NOT use set_req with def-use info.
> >      974 // You can make a new Node with either 'new' or 'clone'.  In either case,
> >      975 // def-use info is (correctly) not generated.
> >      976 // Example: reshape "(X+3)+4" into "X+7":
> >      977 //    set_req(1,in(1)->in(1) /* grab X */, du /* must use DU on 'this' */);
> >      978 //    set_req(2,phase->intcon(7),du);
> >      979 //    return this;
> > -    980 // Example: reshape "X*4" into "X<<1"
> > -    981 //    return new (C,3) LShiftINode( in(1), phase->intcon(1) );
> > +    980 // Example: reshape "X*4" into "X<<2"
> > +    981 //    return new (C,3) LShiftINode( in(1), phase->intcon(2) );
> >      982 //
> >      983 // You must call 'phase->transform(X)' on any new Nodes X you make, except
> > -    984 // for the returned root node.  Example: reshape "X*31" with "(X<<5)-1".
> > -    985 //    Node *shift=phase->transform(new(C,3)LShiftINode(in(1),phase->intcon(5)));
> > -    986 //    return new (C,3) AddINode(shift, phase->intcon(-1));
> > +    984 // for the returned root node.  Example: reshape "X*31" with "(X<<5)-X".
> > +    985 //    Node *shift=phase->transform(new(C,3)LShiftINode(in(1),phase->intcon(5)));
> > +    986 //    return new (C,3) SubINode(shift, phase->intcon(in(1)));
> 
> This last line should probably be 
> 
>  +    986 //    return new (C,3) SubINode(shift, in(1));
> 
> but I admit I'm a noob in this part of the code.  (Which is why I was reading the comments. :-)

I'm not an expert either but it looks good.  I'm adding this one to my
typos-repository.  Thanks!

-- Christian