[Bug optimization/14792] New: [tree-ssa] cast elimination opportunity involving an AND

[Bug optimization/14792] New: [tree-ssa] cast elimination opportunity involving an AND

[kazu at cs dot umass dot edu]

Consider:

void bar (void);

void
foo (unsigned int a)
{
  int b = a;
  if (b & 1)
    bar ();
}

I get:
foo (a)
{
  int b;
  _Bool T.1;
  int T.0;

<bb 0>:
  b_2 = (int)a_1;
  T.0_3 = b_2 & 1;
  T.1_4 = (_Bool)T.0_3;
  if (T.1_4) goto <L0>; else goto <L1>;

<L0>:;
  bar () [tail call];

<L1>:;
  return;

}

We could skip "b" like so

  T.0_3 = a_1 & 1;

-- 
           Summary: [tree-ssa] cast elimination opportunity involving an AND
           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=14792

[Bug optimization/14792] [tree-ssa] cast elimination opportunity involving an AND

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-03-31 03:34 -------
Confirmed, mine.
Here is a better example which causes there to be a reference to link_error (even in RTL):
void link_error (void);
void
foo (char *a)
{
  char b = *a;
  long c = b;
  if (b & 1)
    if (! (c & 1))
      link_error();
}

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |pinskia at gcc dot gnu dot
                   |                            |org
         AssignedTo|unassigned at gcc dot gnu   |pinskia at gcc dot gnu dot
                   |dot org                     |org
             Status|UNCONFIRMED                 |ASSIGNED
     Ever Confirmed|                            |1
   Last reconfirmed|0000-00-00 00:00:00         |2004-03-31 03:34:14
               date|                            |
   Target Milestone|---                         |tree-ssa


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14792

[Bug optimization/14792] [tree-ssa] cast elimination opportunity involving an AND

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-03-31 05:40 -------
On PPC here is why this code is not optimial:
_foo:
        lbz r4,0(r3)
        extsb r0,r4   <--- extra extends byte
        rlwinm r2,r0,0,31,31  <-- as this is just an and 1 (trust me)
        cmpwi cr7,r2,0
        beqlr- cr7
        bnelr- cr7
        b _link_error

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14792

[Bug optimization/14792] [tree-ssa] cast elimination opportunity involving an AND

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-03-31 05:43 -------
Related to, if I fix that case on PPC, it fixes this problem too.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
OtherBugsDependingO|                            |2962
              nThis|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14792

[Bug tree-optimization/14792] [tree-ssa] cast elimination opportunity involving an AND

[pinskia at gcc dot gnu dot org]

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14792

[Bug tree-optimization/14792] [tree-ssa] cast elimination opportunity involving an AND

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-05-24 16:30 -------
For this to work, we have to fold ((int)b & 1) != 0 into b & 1 != 0.  If this is done then the patch for 
15459 can do its work.

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14792

[Bug tree-optimization/14792] [tree-ssa] cast elimination opportunity involving an AND

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-06-01 21:01 -------
I should note that this shows up many times when compiling gcc.

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14792

[Bug tree-optimization/14792] [tree-ssa] cast elimination opportunity involving an AND

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-08-31 04:11 -------
I am not going to fix the fold problem.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
  BugsThisDependsOn|                            |15459
         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=14792