Re: [PATCH] Don't DCE const/pure calls that can throw if cfg can't be altered (PR rtl-optimization/88870)

[Jeff Law <law@redhat.com>]

On 1/16/19 3:43 PM, Jakub Jelinek wrote:
> Hi!
> 
> For normal instructions, deletable_insn_p has:
>   /* Don't delete insns that may throw if we cannot do so.  */
>   if (!(cfun->can_delete_dead_exceptions && can_alter_cfg)
>       && !insn_nothrow_p (insn))
>     return false;
> 
> The following patch adds that for the const/pure non-looping calls
> that are handled earlier in the function as well (I haven't moved this test
> earlier so we don't check insn_nothrow_p on jump insns etc.).
> 
> The other change is just to handle those calls the same as non-const/pure,
> if we never consider them to be deletable, there is no point in
> find_call_stack_args for them, like we don't do that for normal calls.
> 
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
> 
> 2019-01-16  Jakub Jelinek  <jakub@redhat.com>
> 
> 	PR rtl-optimization/88870
> 	* dce.c (deletable_insn_p): Never delete const/pure calls that can
> 	throw if we can't alter the cfg or delete dead exceptions.
> 	(mark_insn): Don't call find_call_stack_args for such calls.
> 
> 	* gcc.dg/pr88870.c: New test.
OK.  Though I wonder if we want to continue to support
-fnon-call-exceptions.  With GCJ gone is there any value left in that
capability?  There's little doubt in my mind other parts of GCC are not
-fnon-call-exception safe.

jeff