[PR middle-end/56108] handle transactions with ASMs in the first block

Richard Henderson rth@redhat.com
Thu Feb 21 17:45:00 GMT 2013


On 02/20/2013 07:35 AM, Aldy Hernandez wrote:
> In the following test, the first statement of a relaxed transaction is
> an inline asm:
> 
>   __transaction_relaxed { __asm__(""); }
> 
> Since we bypass inserting BUILT_IN_TM_IRREVOCABLE at the beginning of
> transactions that are sure to be irrevocable, later when we try to
> expand the transaction, we ICE when we encounter the inline asm.
> 
> Currently, we bypass the TM_IRREVOCABLE call here:
> 
>  for (region = d->all_tm_regions; region; region = region->next)
>     {
>       /* If we're sure to go irrevocable, don't transform anything.  */
>       if (d->irrevocable_blocks_normal
>       && bitmap_bit_p (d->irrevocable_blocks_normal,
>                region->entry_block->index))
>     {
>       transaction_subcode_ior (region, GTMA_DOES_GO_IRREVOCABLE);
>       transaction_subcode_ior (region, GTMA_MAY_ENTER_IRREVOCABLE);
>       continue;
>     }
> 
> If I understand this correctly, ideally a transaction marked as
> doesGoIrrevocable shouldn't bother instrumenting the statements inside,
> since the runtime will go irrevocable immediately.  In which case, we
> can elide the instrumentation altogether as the attached patch does.
> 
> If my analysis is correct, then testsuite/gcc.dg/tm/memopt-1.c would
> surely go irrevocable, thus requiring no instrumentation, causing the
> memory optimizations to get skipped altogether.  In which case, it's
> best to mark the function calls as safe, so they don't cause the
> transaction to become obviously irrevocable.
> 
> Is this correct?  If so, OK?

Yes, that's correct.  The patch is ok.


r~



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