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Re: [avr-gcc-list] Weird optimization issue with avr-gcc 4.5.3, re "nake

From: Bill Westfield
Subject: Re: [avr-gcc-list] Weird optimization issue with avr-gcc 4.5.3, re "naked."
Date: Fri, 27 Jan 2012 16:27:47 -0800

Oops.  I have been forgeting to make sure to cc the list.  And using the wrong 
from address as well...  So I'm going to dump some of the older messages; they 
may be a repeat for some of you.

On Jan 27, 2012, at 3:23 AM, Georg-Johann Lay wrote:

>> 4.5.3 ?  Whatever this issue is, it apparently snuck in between 4.5.2 and 
>> 4.5.3.
> The only remarkable difference between 4.5.2 and 4.5.3 is the fix of PR42240.

That looks exactly relevant.

"The patch implements target hook TARGET_CANNOT_MODIFY_JUMPS_P in order
to inhibit post-reload bb reorder for naked functions."


It looks like the patch to prevent reordering of instructions past the epilogue 
of naked functions prevents such reordering for the entire naked function.

Though I'm not sure I understand why the original complaint was considered a 
bug. They appear to have been counting on a naked C function to fall in at the 
top and fall out at the bottom, which seems like even more of an abuse of 
"naked" than I was using (though I guess allowing that behavior is useful, 
especially in init code.)



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