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: [tree-ssa/java] remaining null-pointer-check hits

On Tuesday 04 May 2004 17:29, wrote:
> I've got the changes necessary to allow DOM to see through these casts
> (it's only a few lines of code).  This picks up most of the cases where
> the RTL null pointer check elimination code was finding something useful
> to do.


> I've also made a trivial extension to DOM which allows it to propagate the
> non-null property through PHI nodes.  ie, if all arguments to a PHI node
> are known to be nonzero, then the result of the PHI node must also be
> nonzero.  That fixed the half-dozen cases we missed in GCC itself.

Isn't this something ccp can do instead?  Or did you add this to keep
all the null checks together in one file?  It's a bit unintiutive that
DOM would have to look through dominance frontiers ;-)

> The net result is we're left one case we're not handling.  Specifically if
> we have multiple paths where a pointer is dereferenced and there is no
> PHI node at their join point.  ie
>     BLOCK1      BLOCK 2
>    p1->field   p1->field
>        \          /
>         \        /
>          \      /
>           \    /
>           BLOCK 3
>           if (p1) ...

How many of these appear in other important software (e.g. kernel, glibc, 

> Anyway, I'll check these bits in once the merge is complete.  Barring
> objections I'll also wipe the RTL null pointer check elimination code.

Whee, one down, NaN to go!


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