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From: "charlie at rivosinc dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/111501] New: RISC-V: non-optimal casting when shifting
Date: Wed, 20 Sep 2023 16:24:13 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D111501

            Bug ID: 111501
           Summary: RISC-V: non-optimal casting when shifting
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: charlie at rivosinc dot com
  Target Milestone: ---

Created attachment 55949
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=3D55949&action=3Dedit
tar file of -save-temps output

I would expect the first to be able to compile into the second:

unsigned int do_shift(unsigned long csum)
{
        return (unsigned short)(csum >> 32);
}

unsigned int do_shift2(unsigned long csum)
{
        return (csum << 16) >> 48;
}

However, the asm output is instead:

do_shift:
        srli    a0,a0,32
        slli    a0,a0,48
        srli    a0,a0,48
        ret
do_shift2:
        slli    a0,a0,16
        srli    a0,a0,48
        ret

These are the same so the first should be able to be compiled into the seco=
nd.=