This is the mail archive of the mailing list for the GCC project.

Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]
Other format: [Raw text]

Re: [PATCH] Fix PR28268, ICE building vector const { 1, 1 }

Richard Guenther <> writes:

> > This makes me uncomfortable.  The number zero seems like a special
> > case which merits special handling.  The number one does not.  What
> > you are looking for is a function which returns the multiplicative
> > identity for TYPE.  Currently you are getting it by calling
> > fold_convert (TYPE, integer_one_node).  Suppose you write the
> > multiplicative identify function, and handle VECTOR_TYPE there, rather
> > than making the number one a special case in fold_convert?
> > 
> > Otherwise I think you need to give some justification for why
> > fold_convert should not permit any constant for VECTOR_TYPE.  And it's
> > hard to see what that justification should be.
> My reasoning was that as zero (identity for addition), one is a special 
> number (identity for multiplication).  There's one other special number
> that one could add, -1, which represents a "sign", but that stretches
> the argument a bit.

The number zero is special for several reasons.  In particular, we
probably use it when clearing memory.

The number one does not seem to me to have the same properties.

> The other fix I was thinking about is simply punting on VECTOR_TYPE
> arguments completely for the optimizations in fold_plusminus_mult_expr.

Sure, that is the easy way.


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]