Re: [PATCH] combine: Fix PR80233

[Jeff Law <law@redhat.com>]

On 03/29/2017 12:23 PM, Segher Boessenkool wrote:
> If combine has added an unconditional trap there will be a new basic
> block as well.  It will then end up considering the NOTE_INSN_BASIC_BLOCK
> as the last_combined_insn, but then it tries to take the DF_INSN_LUID
> of that and that dereferences a NULL pointer (since such a note is not
> an INSN_P).
>
> This fixes it by not taking non-insns as last_combined_insn.
>
> Bootstrapped and tested on powerpc64-linux {-m32,-m64}.
>
>
> Segher
>
>
> 2017-03-29  Segher Boessenkool  <segher@kernel.crashing.org>
>
> 	PR rtl-optimization/80233
> 	* combine.c (combine_instructions): Only take NONDEBUG_INSN_P insns
> 	as last_combined_insn.  Do not test for BARRIER_P separately.
>
> gcc/testsuite/
> 	PR rtl-optimization/80233
> 	* gcc.c-torture/compile/pr80233.c: New testcase.
No strong opinions on this vs Jakub's patch.  I guess yours may walk 
more objects on the chain, but in doing so is more likely to find a 
useful LAST_COMBINED_INSN.  Jakub's stops earlier, but is less likely to 
have stopped on something useful.

Your call Segher.

jeff

ps.  Never in a million years would I have expected isolation of 
division by zero to have exposed as many latent issues as it has.  Sigh.