[Bug middle-end/30984] [4.1/4.2/4.3 Regression] ICE with computed goto and constants

["law at redhat dot com" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #3 from law at redhat dot com  2007-03-12 20:06 -------
Subject: Re:  [4.1/4.2/4.3 Regression] ICE with
        computed goto and constants

On Mon, 2007-03-12 at 19:45 +0000, janis at gcc dot gnu dot org wrote:
> 
> ------- Comment #2 from janis at gcc dot gnu dot org  2007-03-12 19:45 -------
> A regression hunt on powerpc-linux using the submitter's test case identified
> this patch:
> 
>     http://gcc.gnu.org/viewcvs?view=rev&rev=96084
> 
>     r96084 | law | 2005-03-08 03:39:19 +0000 (Tue, 08 Mar 2005)
Thanks for alerting me to this problem.  I think the right fix is going
to simply be to enforce a rule that we can only optimize a computed goto
if the argument collapses down to a local LABEL_REF rather than a
generic invariant. 

In the case where we have a constant or non-local LABEL_REF, the CFG
(before optimizing) ought to be conservatively correct(*).  Optimizing
is impossible because we don't know which outgoing edge to keep and
which ones to throw away.

This ought to be a 1-2 line fix.

Jeff

(*)  If the argument referred to a constant address in the current
function which does not correspond to any known addressable LABEL_REF
then we're hosed as the original unoptimized CFG is probably bogus.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30984