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Re: [PATCH] combine: Allow combining two insns to two insns


On Tue, Jul 24, 2018 at 05:18:41PM +0000, Segher Boessenkool wrote:
> This patch allows combine to combine two insns into two.  This helps
> in many cases, by reducing instruction path length, and also allowing
> further combinations to happen.  PR85160 is a typical example of code
> that it can improve.
> 
> This patch does not allow such combinations if either of the original
> instructions was a simple move instruction.  In those cases combining
> the two instructions increases register pressure without improving the
> code.  With this move test register pressure does no longer increase
> noticably as far as I can tell.
> 
> (At first I also didn't allow either of the resulting insns to be a
> move instruction.  But that is actually a very good thing to have, as
> should have been obvious).
> 
> Tested for many months; tested on about 30 targets.
> 
> I'll commit this later this week if there are no objections.

Done now, with the testcase at https://gcc.gnu.org/ml/gcc-patches/2018-07/msg01856.html .


Segher


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