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From: "segher at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug middle-end/82940] Suboptimal code for (a & 0x7f) | (b & 0x80)
 on powerpc
Date: Mon, 23 Aug 2021 15:40:43 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D82940

--- Comment #7 from Segher Boessenkool <segher at gcc dot gnu.org> ---
(In reply to Peter Cordes from comment #6)
> # power64 GCC 9.2.1 (ATI13.0)
>         rlwimi 3,4,0,255    # bit-blend according to mask, rotate count=
=3D0
>         rldicl 3,3,0,32     # Is this zero-extension to 64-bit redundant?

It is: the rlwinm does an AND with 0xff already, so that clears the top 32
bits for sure.

> But ppc64 GCC does zero-extension of the result from 32 to 64-bit, which =
is
> probably not needed unless the calling convention has different requireme=
nts
> for return values than for incoming args.  (I don't know PPC well enough.)

Return values have to be properly (sign- or zero-) extended for its type,
just like function arguments.=