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From: "ebotcazou at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/109040] [13 Regression] wrong code with v16hi compare &
 mask on riscv64 at -O2 since r13-4907-g2e886eef7f2b5a
Date: Tue, 04 Apr 2023 20:08:36 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D109040

--- Comment #7 from Eric Botcazou <ebotcazou at gcc dot gnu.org> ---
WORD_REGISTER_OPERATIONS means that subword register operations in RTL are
actually performed on the whole word register by the machine, e.g.. for

(insn 47 35 39 2 (set (reg:HI 175)
        (subreg:HI (reg:SI 166) 0)) "pr109040.c":9:11 179 {*movhi_internal}
     (expr_list:REG_DEAD (reg:SI 166)
        (nil)))

you can infer the MSB of (reg:SI 175) instead of them being undefined.  But=
 I
don't think that it prevents any particular instruction form.=