Re: [PATCH] Fix PR tree-optimization/58137

[Richard Biener <richard dot guenther at gmail dot com>]

On Tue, Aug 20, 2013 at 1:01 PM, Bernd Edlinger
<bernd.edlinger@hotmail.de> wrote:
> This patch fixes a bug in the vectorized pointer arithmetic in the forwprop
> optimization pass.
>
> Although it seems to be impossible to create a vector of pointers with the
> __attribute__((vector_size(x))) syntax, the vector loop optimization together
> with the loop unrolling can create code which adds a vector of ptroff_t
> repeatedly to a vector of pointers.
>
> The code in tree-ssa-forwprop.c handles program transformations of the
> form (PTR +- CST1) +- CST2 => PTR +- (CST1+-CST2) where PTR is
> a vector of pointers and CST1 and CST2 are vectors of ptroff_t, without the
> fix the result type of CST1+-CST2 was vector of pointer, which causes the
> ICE in tree-cfg.c, which sees an undefined pointer + pointer operation.
>
> Additionally the check in tree-cfg.c allows expressions of the form CST - PTR,
> which is clearly wrong. That should be fixed too.
>
> The patch was bootstrapped and regression tested on i686-pc-linux-gnu.

It seems to me that the forwprop code does not handle the fact that we
are permissive as to using PLUS_EXPR instead of POINTER_PLUS_EXPR
for vector pointer - offset additions.  So instead of doing this dance the
better (and more easily backportable) fix is to simply disable the transform
on pointer valued PLUS_EXPR.  Like with

  if (POINTER_TYPE_P (TREE_TYPE (gimple_assign_lhs (stmt))))
    return false;

at the beginning of the function.

The real fix is of course to make vector pointer operations properly
use POINTER_PLUS_EXPR ...

Richard.



> Regards
> Bernd Edlinger