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RE: [PATCH] [Aarch64] Optimize subtract in shift counts


Correct.

-----Original Message-----
From: Richard Kenner [mailto:kenner@vlsi1.ultra.nyu.edu] 
Sent: Tuesday, August 8, 2017 1:20 PM
To: Michael Collison <Michael.Collison@arm.com>
Cc: gcc-patches@gcc.gnu.org; nd <nd@arm.com>; pinskia@gmail.com
Subject: RE: [PATCH] [Aarch64] Optimize subtract in shift counts

> Correct. It is truncated for integer shift, but not simd shift 
> instructions. We generate a pattern in the split that only generates 
> the integer shift instructions.

That's unfortunate, because it would be nice to do this in simplify_rtx, since it's machine-independent, but that has to be conditioned on SHIFT_COUNT_TRUNCATED, so you wouldn't get the benefit of it.


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