[PATCH, rs6000] Fixing PR 67145

Segher Boessenkool segher@kernel.crashing.org
Fri Feb 26 21:43:00 GMT 2016


On Fri, Feb 26, 2016 at 01:10:17PM -0800, Richard Henderson wrote:
> On 02/26/2016 01:01 PM, Segher Boessenkool wrote:
> >> How do you imagine the rs6000 change will regress codegen?
> > 
> > Combine of sequences with double-length adds.
> 
> What sort of test case are you imagining here?  The trivial tests I've looked
> at have all been optimal (before and after).

There are many different combinations, for example (32-bit code)

long long add_s42(long long a, int b)
{
	return a + ((long long) b << 32) + 42;
}

and we generate optimal code on BE for all of those (not on LE yet,
and there is the issue with open-coded carry chains, and and and, and
things shift around.  Also all the scc things.  But I really should
submit some testcases).


Segher



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