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Re: [Patch, testsuite, mips] Fix two failing MIPS tests.


Steve Ellcey <sellcey@mips.com> writes:
> On Sat, 2014-05-03 at 07:52 +0100, Richard Sandiford wrote:
>
>> > Old:
>> >
>> >  	li	$5,305397760			# 0x12340000
>> >  	addiu	$4,$5,1
>> >  	addiu	$5,$5,-1
>> >
>> > New:
>> >
>> > 	li	$5,305332224			# 0x12330000
>> >  	ori	$5,$5,0xffff
>> >  	addiu	$4,$5,2
>> 
>> This isn't as good though -- $4 now depends on two previous
>> instructions.  Do you know which specific change was responsible?
>> 
>> Thanks,
>> Richard
>
> A quick follow up.  The code in question is:
>
>     void f () { g (0x12340001, 0x1233ffff); }
>
> And if I swap the arguments I get something more like the old code.
> But if I run an older GCC on that new swapped code then I get something
> like the new code.  So while the old code may have been better for this
> example, the new code is better if I swap the arguments around.

OK, in that case it sounds like the optimisation wasn't working as well
as it was supposed to.  But I think we should fix that rather than change
the expected output.  AFAICT the new output means the const-anchor
optimisation isn't kicking in.

Thanks,
Richard




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