[RFA][PATCH][PR middle-end/59285] BARRIERS and merged blocks

Jeff Law law@redhat.com
Wed Jan 8 05:54:00 GMT 2014


On 01/07/14 01:08, Steven Bosscher wrote:
> On Tuesday, January 7, 2014, Jeff Law wrote:
>
>     On 12/24/13 13:19, Steven Bosscher wrote:
>
>         For GCC 4.10
>
>         we should define what behavior should result from
>         builtin_unreachable
>         (Should it trap? Can it be optimized away after a while to avoid
>         these
>         unnecessary conditional jumps? ...) but for the moment it seems
>         wrong
>         IMHO to only optimize this in the cond_exec case and to do so
>         against
>         the rules of the control flow graph.
>
>     This problem can (and should) be addressed independently of a review
>     of the __builtin_unreachable semantics.
>
>
> Agreed.
:-)

>
>
>
>         Something like the patch below, tested with a cross-compiler for
>         arm-eabi.
>         What do you think of this approach?
>
>
>                   PR middle-end/59285
>                   * ifcvt. (cond_exec_find_if_block): Do not try to
>         if-convert an empty
>                   basic block without successors due to builtin_unreachable.
>
>     I still prefer my most recent patch.
>
>     jeff
>
>
>
> Ok!
Thanks.  One more P1 off the list :-)

jeff



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