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From: "bina2374 at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/95632] New: Redundant zero extension
Date: Thu, 11 Jun 2020 04:06:40 +0000
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: target
X-Bugzilla-Version: 10.1.0
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X-Bugzilla-Priority: P3
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D95632

            Bug ID: 95632
           Summary: Redundant zero extension
           Product: gcc
           Version: 10.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: bina2374 at gmail dot com
                CC: kito at gcc dot gnu.org, wilson at gcc dot gnu.org
  Target Milestone: ---
            Target: riscv32-unknown-elf

Command line: bin/riscv64-unknown-elf-gcc -march=3Drv32imafc -mabi=3Dilp32f=
 -O2
foo.c -S

=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
 C Source
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
unsigned short foo(unsigned short crc) {
  crc ^=3D 0x4002;
  crc >>=3D 1;
  crc |=3D 0x8000;

  return crc;
}

=3D=3D=3D=3D=3D=3D=3D=3D=3D
 GCC asm
=3D=3D=3D=3D=3D=3D=3D=3D=3D
foo:
        li      a5,-24576  #
        addi    a5,a5,1    # a5 =3D 0xffffa001
        srli    a0,a0,1
        xor     a0,a0,a5
        slli    a0,a0,16   #=20
        srli    a0,a0,16   # redundant zero-extension
        ret

=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
 Ideal Code Generation=20
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
foo:
        li      a5,40960   #
        addi    a5,a5,1    # a5 =3D 0x0000a001
        srli    a0,a0,1
        xor     a0,a0,a5
        ret=