Re: RFA PR middle-end/48770

[Jeff Law <law@redhat.com>]

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On 05/30/11 04:55, Bernd Schmidt wrote:
> On 05/27/2011 07:49 PM, Jeff Law wrote:
>> Updated based on some comments from Bernd; specifically the other use of
>> delete_dead_insn has been removed.
>>
>> WRT the assembly differences on MIPS Bernd referred to; what ultimately
>> caused this problem were two dead insns that had been previously
>> eliminated by reload were still in the insn stream and inhibited an
>> if-conversion which resulted in slightly different assembly code, but
>> shouldn't have had any significant impact on the performance or size of
>> the resulting code.  The dead insns were deleted by the post-reload DCE
>> pass (which obviously runs after post-reload if conversion).
>>
>> If we really wanted to get those insns out of the stream, we could flag
>> when reload deleted insns which might result in dead code remaining in
>> the stream, then conditionally run DCE immediately after reload.  I
>> didn't think this was worth doing right now, but if someone objects I
>> can certainly look into it.
> 
> Patch is OK (still no codegen changes on x86 as far as I can tell), but
> I'd appreciate the DCE thing as a followup.
I suspect it's going to be just as easy to go ahead and add the DCE
cleanup now rather than waiting.  It should be a relatively trivial
tweak to delete_dead_insn to set a flag which we'd check at the end of
reload.  It's #2 in the queue :-)


jeff
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