Re: [PATCH] sched1: Fix -fcompare-debug issue in schedule_region [PR105586]

[Jeff Law <jeffreyalaw@gmail.com>]

On 8/23/2022 5:49 AM, Surya Kumari Jangala via Gcc-patches wrote:
> sched1: Fix -fcompare-debug issue in schedule_region [PR105586]
>
> In schedule_region(), a basic block that does not contain any real insns
> is not scheduled and the dfa state at the entry of the bb is not copied
> to the fallthru basic block. However a DEBUG insn is treated as a real
> insn, and if a bb contains non-real insns and a DEBUG insn, it's dfa
> state is copied to the fallthru bb. This was resulting in
> -fcompare-debug failure as the incoming dfa state of the fallthru block
> is different with -g. We should always copy the dfa state of a bb to
> it's fallthru bb even if the bb does not contain real insns.
>
> 2022-08-22  Surya Kumari Jangala  <jskumari@linux.ibm.com>
>
> gcc/
> 	PR rtl-optimization/105586
> 	* sched-rgn.cc (schedule_region): Always copy dfa state to
> 	fallthru block.
>
> gcc/testsuite/
> 	PR rtl-optimization/105586
> 	* gcc.target/powerpc/pr105586.c: New test.
Interesting.    We may have stumbled over this bug internally a little 
while ago -- not from a compare-debug standpoint, but from a "why isn't 
the processor state copied to the fallthru block" point of view.   I had 
it on my to investigate list, but hadn't gotten around to it yet.

I think there were requests for ChangeLog updates and a function comment 
for save_state_for_fallthru_edge.  OK with those updates.

jeff