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From: "segher at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug target/100866] PPC: Inefficient code for vec_revb(vector
 unsigned short) < P9
Date: Wed, 23 Jun 2021 20:06:33 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D100866

--- Comment #14 from Segher Boessenkool <segher at gcc dot gnu.org> ---
(In reply to luoxhu from comment #13)
> It is not visible in combine due to the constant data is in *.LC0 and

combine can see things in the constant pool in various ways though (just
like many other parts of the compiler).  But yeah, unspecs are a big
hurdle to optimisation always.  If we would express this as some "real"
RTL we would need a few variants: one that takes only one register as
data input and another that takes two; one that has all permutation
indices in range and another that masks them; and maybe a few more.=