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From: "pluto at agmk dot net" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/52231] New: [missed optimization/diagnostics] address-of-reference
Date: Mon, 13 Feb 2012 13:33:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52231

             Bug #: 52231
           Summary: [missed optimization/diagnostics] address-of-reference
    Classification: Unclassified
           Product: gcc
           Version: 4.6.3
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: pluto@agmk.net


int& singleton();
void foo();
void bar()
{
        int& a = singleton();
        int& b = singleton();
        if ( &a == 0 )         <== useless stmt (not diagnosed/not optimized)
                foo();
        a = 5;
        if ( b != 5 )
                foo();
}

in c++ the adress of refer

$ g++ 0.cpp -O2 -Wall -Wextra -fdump-tree-optimized -c && cat
0.cpp.143t.optimized

void bar() ()
{
  int & D.2079;
  int & D.2078;
  int D.2074;
<bb 2>:
  D.2078_1 = singleton ();
  D.2079_3 = singleton ();
  if (D.2078_1 == 0B)          <========
    goto <bb 3>;
  else
    goto <bb 4>;
<bb 3>:
  foo ();
<bb 4>:
  *D.2078_1 = 5;
  D.2074_5 = *D.2079_3;
  if (D.2074_5 != 5)
    goto <bb 5>;
  else
    goto <bb 6>;
<bb 5>:
  foo (); [tail call]

<bb 6>:
  return;
}