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Date: Mon, 26 May 2003 13:58:00 -0000
From: "pb@gcc.gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Message-ID: <20030526135310.10982.pb@gcc.gnu.org>
Reply-To: gcc-bugzilla@gcc.gnu.org
Subject: [Bug optimization/10982] New: [arm] poor optimisation of "if (var & const)"
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X-SW-Source: 2003-05/txt/msg02851.txt.bz2
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=10982

           Summary: [arm] poor optimisation of "if (var & const)"
           Product: gcc
           Version: unknown
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: optimization
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: pb@gcc.gnu.org
                CC: gcc-bugs@gcc.gnu.org
GCC target triplet: arm-linux

Compiling this code:

f(int a)
{
  if (a & 0xfff)
    return 1;
  return 0;
}

with -O2 yields:

        mov     r0, r0, asl #20
        mov     r0, r0, lsr #20
        cmp     r0, #0
        movne   r0, #1
        moveq   r0, #0

There's no need to fully calculate the value of the AND, since all that we care
about is whether it's zero or not.  So, I think the first three instructions
could be replaced by a single one:

        movs     r0, r0, asl #20



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