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Date: Sun, 27 Nov 2005 02:30:00 -0000
Subject: [Bug target/25113]  New: [m68k] lshiftrt and some other insns are conservative on cc0
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From: "kazu at gcc dot gnu dot org" <gcc-bugzilla@gcc.gnu.org>
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Consider:

unsigned int bar (void);

void
foo (void)
{
  unsigned int a = bar ();
  a >>= 2;
  if (a == 0)
    bar ();
}

./cc1 -quiet -O2 -m5200 -fomit-frame-pointer generates

foo:
        move.l %a2,-(%sp)
        lea bar,%a2
        jbsr (%a2)
        lsr.l #2,%d0
        tst.l %d0
        jbne .L4
        jbsr (%a2)
.L4:
        move.l (%sp)+,%a2
        rts

Note that tst.l is not necessary because lsr.l sets the zero flag correctly.

See notice_update_cc and its frequent use of CC_STATUS_INIT.


-- 
           Summary: [m68k] lshiftrt and some other insns are conservative on
                    cc0
           Product: gcc
           Version: 4.2.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: normal
          Priority: P3
         Component: target
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: kazu at gcc dot gnu dot org
GCC target triplet: m68k-elf


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25113