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Date: Wed, 14 Jul 2004 13:57:00 -0000
From: "steven at gcc dot gnu dot org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Message-ID: <20040714135701.16538.steven@gcc.gnu.org>
Reply-To: gcc-bugzilla@gcc.gnu.org
Subject: [Bug tree-optimization/16538] New: Missed jump threading opportunity with struct fields (but RTL thread_jumps does catch it)
X-Bugzilla-Reason: CC
X-SW-Source: 2004-07/txt/msg01702.txt.bz2
List-Id: <gcc-bugs.sourceware.org>

We are missing a few jump threading opportunities
of the following form in SPEC and in GCC itself:

------------------------------------------------
struct foo
{
  int field1;
  int field2;
};

struct foo glob;

void
bar (void)
{
  struct foo *g1, *g2;
  g1 = g2 = &glob;
  int i;

  if (!g1->field1)
    g1->field2 = g1->field1;

  if (!g2->field1)
    g2->field2 = g2->field1;
}
------------------------------------------------


The .optimized dump looks like this:

;; Function bar (bar)

bar ()
{
  int i;
  struct foo * g2;
  struct foo * g1;
  int T.1;
  int T.0;

<bb 0>:
  if (glob.field1 == 0) goto <L0>; else goto <L1>;

<L0>:;
  glob.field2 = 0;

<L1>:;
  if (glob.field1 == 0) goto <L2>; else goto <L3>;

<L2>:;
  glob.field2 = 0;

<L3>:;
  return;

}


We eventually end up threading this jump on RTL.

-- 
           Summary: Missed jump threading opportunity with struct fields
                    (but RTL thread_jumps does catch it)
           Product: gcc
           Version: 3.5.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: normal
          Priority: P2
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: steven at gcc dot gnu dot org
                CC: dnovillo at redhat dot com,gcc-bugs at gcc dot gnu dot
                    org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16538