[Bug optimization/14844] New: [tree-ssa] narrow types if wide result is not needed

[Bug optimization/14844] New: [tree-ssa] narrow types if wide result is not needed

[kazu at cs dot umass dot edu]

Consider:

int
foo (int a, int b)
{
  long long aa = a;
  long long bb = b;
  return aa + bb;
}

The last tree looks like:

foo (a, b)
{
<bb 0>:
  return (int)(long long int)a + (int)(long long int)b;

}

We may be able to solve this problem by propagating narrowing casts backward.

-- 
           Summary: [tree-ssa] narrow types if wide result is not needed
           Product: gcc
           Version: tree-ssa
            Status: UNCONFIRMED
          Keywords: pessimizes-code
          Severity: enhancement
          Priority: P2
         Component: optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: kazu at cs dot umass dot edu
                CC: gcc-bugs at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14844

[Bug optimization/14844] [tree-ssa] narrow types if wide result is not needed

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-04-04 16:20 -------
Confirmed, but already fixed by my cast patch: <http://gcc.gnu.org/ml/gcc-patches/2004-04/
msg00169.html>.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |pinskia at gcc dot gnu dot
                   |dot org                     |org
             Status|UNCONFIRMED                 |ASSIGNED
     Ever Confirmed|                            |1
           Keywords|                            |patch
   Last reconfirmed|0000-00-00 00:00:00         |2004-04-04 16:20:45
               date|                            |
   Target Milestone|---                         |tree-ssa


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14844

[Bug optimization/14844] [tree-ssa] narrow types if wide result is not needed

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-04-05 01:12 -------
An other expample but it is not fixed by my patch (but I should handle though):
int
foo (int a, int b)
{
  long long aa = a;
  long long bb = b;
  long long cc = aa + bb;
  int dd = cc;
  return dd;
}

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|patch                       |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14844

[Bug optimization/14844] [tree-ssa] narrow types if wide result is not needed

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-04-06 00:06 -------
It is a memory hug and a compile time hog because the number of RTL produced is too 
much.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |compile-time-hog, memory-
                   |                            |hog, TREE


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14844

[Bug optimization/14844] [tree-ssa] narrow types if wide result is not needed

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-04-06 18:08 -------
Also it does not get optimized untill after register allocation which is bad news for some 
targets like x86.

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14844

[Bug tree-optimization/14844] [tree-ssa] narrow types if wide result is not needed

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-05-17 14:05 -------
Once fold is able to do (int)(a+b) into (int)a + (int)b, the combine pass (15459) should be able to fix 
this.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
  BugsThisDependsOn|                            |15459


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14844

[Bug tree-optimization/14844] [tree-ssa] narrow types if wide result is not needed

[pinskia at gcc dot gnu dot org]

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|3.5.0                       |---


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14844

[Bug tree-optimization/14844] [tree-ssa] narrow types if wide result is not needed

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-06-21 05:08 -------
Well I am not going to fix this one yet.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|pinskia at gcc dot gnu dot  |unassigned at gcc dot gnu
                   |org                         |dot org
             Status|ASSIGNED                    |NEW


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14844

[Bug tree-optimization/14844] [tree-ssa] narrow types if wide result is not needed

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2005-02-14 02:23 -------
Note the code from build_binop from the C and C++ front-ends need to be moved to fold and then 
when that happens my tree combiner will just work.

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14844

[Bug tree-optimization/14844] [tree-ssa] narrow types if wide result is not needed

[schlie at comcast dot net]

------- Additional Comments From schlie at comcast dot net  2005-02-14 05:47 -------
(In reply to comment #7)
> Note the code from build_binop from the C and C++ front-ends need to be moved to fold and then 
> when that happens my tree combiner will just work.

Sorry, but a little confused, as it's perfectly correct to shorten these operands to the width
of the operation's assignment, and in fact should be done? (so there's nothing to correct
and arguably should have been identifyed as such by the front-ends to begin with it would seem)

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14844

[Bug tree-optimization/14844] [tree-ssa] narrow types if wide result is not needed

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2005-02-14 05:57 -------
(In reply to comment #8)
> Sorry, but a little confused, as it's perfectly correct to shorten these operands to the width
> of the operation's assignment, and in fact should be done? (so there's nothing to correct
> and arguably should have been identifyed as such by the front-ends to begin with it would seem)

What I was trying to say, is that this should not be done in the front-end as the front-end has almost 
no business to deal with optimizations.

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14844