On Wed, 2020-02-19 at 12:59 +0000, Richard Sandiford wrote:
> This PR is about a case in which the clobbers at the start of
> an EH receiver can lead to registers becoming unnecessarily
> live in predecessor blocks. My first attempt at fixing this
> made sure that we update the bb liveness info based on the
> real live set:
>
> http://gcc.gnu.org/g:e648e57efca6ce6d751ef8c2038608817b514fb4
>
> But it turns out that the clobbered registers were also added to
> the "gen" set of LRA's private liveness problem, where "gen" in
> this context means "generates a requirement for a live value".
> So the clobbered registers could still end up live via that
> mechanism instead.
>
> This patch therefore reverts the patch above and takes the other
> approach floated in the original patch description: model the full
> clobber by making the registers live and then dead again.
>
> There's no specific need to revert the original patch, since the
> code should no longer be sensitive to the order of the bb liveness
> update and the modelling of the clobber. But given that there's
> no specific need to keep the original patch either, it seemed better
> to restore the code to the more well-tested order.
>
> Tested on aarch64-linux-gnu and x86_64-linux-gnu. OK to install?
>
> Richard
>
>
> 2020-02-19 Richard Sandiford <richard.sandif...@arm.com>
>
> gcc/
> PR rtl-optimization/PR92989
> * lra-lives.c (process_bb_lives): Restore the original order
> of the bb liveness update. Call make_hard_regno_dead for each
> register clobbered at the start of an EH receiver.
THanks. Installed.
jeff
>
