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Date: Thu, 01 Sep 2005 00:40:00 -0000
From: "pinskia at gcc dot gnu dot org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Message-ID: <20050901004014.23664.pinskia@gcc.gnu.org>
Reply-To: gcc-bugzilla@gcc.gnu.org
Subject: [Bug middle-end/23664] New: fold does not change (a&C1)+(b&C2) to (a&C1)|(b&C2) iff (C1 & C2) == 0
X-Bugzilla-Reason: CC
X-SW-Source: 2005-09/txt/msg00000.txt.bz2
List-Id: <gcc-bugs.sourceware.org>

These two functions should produce the same asm:
int f(int a, int b)
{
  return (a&0xF)+(b&0xF0);
}
int f1(int a, int b)
{
  return (a&0xF)|(b&0xF0);
}
For PPC, we get:
_f:
        rlwinm r4,r4,0,24,27
        rlwinm r3,r3,0,28,31
        add r3,r3,r4
        blr
_f1:
        rlwinm r4,r4,0,24,27
        rlwimi r3,r4,0,0,27
        blr

Which shows the | is more efficient than the + one.

-- 
           Summary: fold does not change (a&C1)+(b&C2) to (a&C1)|(b&C2) iff
                    (C1 & C2) == 0
           Product: gcc
           Version: 4.1.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: enhancement
          Priority: P2
         Component: middle-end
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: pinskia at gcc dot gnu dot org
                CC: gcc-bugs at gcc dot gnu dot org
GCC target triplet: powerpc-*-*
OtherBugsDependingO 19987
             nThis:


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23664