This case is covered by Wilco's previous reply:
From: Richard Kenner [mailto:ken...@vlsi1.ultra.nyu.edu]
Sent: Tuesday, August 8, 2017 5:13 AM
To: Michael Collison <michael.colli...@arm.com>
Cc: firstname.lastname@example.org; nd <n...@arm.com>; pins...@gmail.com
Subject: RE: [PATCH] [Aarch64] Optimize subtract in shift counts
> The pattern will only be matched if the value is positive. More
> specifically if the constant value is 32 (SImode) or 64 (DImode).
I don't mean the constant, but the value subtracted from it.
If that's negative, then we have a shift count larger than the wordsize.