[Bug tree-optimization/30997] New: FRE does not value number comparisons in COND_EXPRs

[Bug tree-optimization/30997] New: FRE does not value number comparisons in COND_EXPRs

[rguenth at gcc dot gnu dot org]

int foo(int a) { int tmp = a > 2; if (a > 2) return tmp; }

is not simplified.


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           Summary: FRE does not value number comparisons in COND_EXPRs
           Product: gcc
           Version: 4.3.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: enhancement
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: rguenth at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30997

[Bug tree-optimization/30997] FRE does not value number comparisons in COND_EXPRs

[pinskia at gcc dot gnu dot org]

------- Comment #1 from pinskia at gcc dot gnu dot org  2007-02-28 19:20 -------
well that is undefined code anyways :)

int foo(int a) { int tmp = a > 2; if (a > 2) return tmp; return 10;}

Note we do simplify this later on after PRE/FRE as we sink the a>2 into the
other basic block and then VRP comes about and finds it is always true.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30997

[Bug tree-optimization/30997] FRE does not simplify comparisons in COND_EXPRs

[rguenth at gcc dot gnu dot org]

------- Comment #2 from rguenth at gcc dot gnu dot org  2007-12-03 15:44 -------
Re-confirmed with SCCVN.  Note that while it value numbers the COND_EXPR on
the RHS it does not simplify the condition in the COND_EXPR stmt:

Value numbering tmp_3 stmt = tmp_3 = a_2(D) > 2;
Setting value number of tmp_3 to tmp_3

<bb 2>:
  tmp_3 = a_2(D) > 2;
  if (a_2(D) > 2)
    goto <bb 4>;
  else
    goto <bb 3>;

Even if you teach FRE to do elimination in COND_EXPR statements (which it
does not do), the COND_EXPR condition has no value handle associated and
a lookup with the expression in the PRE table fails.


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rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |dberlin at gcc dot gnu dot
                   |                            |org
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2007-12-03 15:44:44
               date|                            |
            Summary|FRE does not value number   |FRE does not simplify
                   |comparisons in COND_EXPRs   |comparisons in COND_EXPRs


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30997

[Bug tree-optimization/30997] FRE does not simplify comparisons in COND_EXPRs

[rguenth at gcc dot gnu dot org]

------- Comment #3 from rguenth at gcc dot gnu dot org  2008-03-28 19:21 -------
SCCVN now tries to simplify COND_EXPR conditions using their operands value
number.  This still doesn't remove redundant comparisons.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30997