[Bug optimization/15017] New: [tree-ssa] compare (equal) with casts are not removed

[Bug optimization/15017] New: [tree-ssa] compare (equal) with casts are not removed

[pinskia at gcc dot gnu dot org]

On most targets where _Bool is of size 1 (everywhere except PPC-darwin), the following
code contains sign/zero extends which is bad code:

static _Bool as, bs;
_Bool foo3 (void) {
if (as != bs) return 1;
else  return 0;
}

Likewise for this code also:
static signed char as, bs;
_Bool foo3 (void) {
int as1 = as;
int bs1 = bs;
if (as1 != bs1) return 1;
else  return 0;
}

-- 
           Summary: [tree-ssa] compare (equal) with casts are not removed
           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: pinskia at gcc dot gnu dot org
                CC: gcc-bugs at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=15017

[Bug optimization/15017] [tree-ssa] compare (equal) with casts are not removed

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-04-20 01:09 -------
I will try to fix this but only after I finish my current projects: the cast pass, non-lowering 
patch/offsetof, and fixing Darwin's back-end.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |dann at godzilla dot ics dot
                   |                            |uci dot edu
         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         |2004-04-20 01:09:48
               date|                            |
   Target Milestone|---                         |tree-ssa


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=15017

[Bug optimization/15017] [tree-ssa] compare (equal) with casts are not removed

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-04-20 01:16 -------
Here is an example which messes up on powerpc (lha is slower than lhz):
static short as, bs;
_Bool foo3 (void) {
int as1 = as;
int bs1 = bs;
if (as1 != bs1) return 1;
else  return 0;
}

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=15017

[Bug optimization/15017] [tree-ssa] compare (equal) with casts are not removed

[dann at godzilla dot ics dot uci dot edu]

------- Additional Comments From dann at godzilla dot ics dot uci dot edu  2004-04-20 14:15 -------
It seems that the underlying problem is casting bools to int before
using them.

For example look at the .original dump:

;; Function foo0 (foo0)
;; enabled by -tree-original

{
   if ((int)a != 0)
      return <return-value> = 1;
   else
       return <return-value> = 0;

}

The cast does not seem to be needed, != can take a bool as an argument. 
Not emitting casts there will simplify the work the optimizers have to do. 

I only gave you one function, here is the file I was playing with:

_Bool foo (_Bool a, _Bool b)
{
  if (a != b)
    return 1;
  else
    return 0;
}

_Bool foo0 (_Bool a)
{
  if (a)
    return 1;
  else
    return 0;
}

_Bool bar (_Bool a)
{
  return a;
}

_Bool foo1 (_Bool a, _Bool b)
{
  if (bar(a))
    return 1;
  else
    return 0;
}

struct mm
{
  _Bool a;
  _Bool b;
} T;

_Bool foo2 (void)
{
  if (T.a != T.b)
    return 1;
  else
    return 0;
}

static _Bool as, bs;
_Bool foo3 (void) {
  if (as != bs) return 1;
  else  return 0;
}


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=15017

[Bug optimization/15017] [tree-ssa] compare (equal) with casts are not removed

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-04-20 14:34 -------
And here is the tree dump for patches which I have in my local tree (my cast pass and addition to PHI-
OPT to work with different types and one which combines the return statements):

;; Function foo (foo)

foo (a, b)
{
<bb 0>:
  return ((int)a != (int)b);  <-- conversion to int not needed

}

;; Function foo0 (foo0)

foo0 (a)
{
<bb 0>:
  return (a != 0);  <-- same as a cast to int, I have to think of a better way of doing this.

}



;; Function bar (bar)

bar (a)
{
<bb 0>:
  return (int)a;  <-- good code as _Bool is promoted to int by the ABI

}



;; Function foo2 (foo2)

foo2 ()
{
<bb 0>:
  return ((int)T.a != (int)T.b);  <--- extranous casts

}



;; Function foo3 (foo3)

foo3 ()
{
<bb 0>:
  return ((int)as != (int)bs);  <--- likewise

}



;; Function foo1 (foo1)

foo1 (a, b)
{
<bb 0>:
  return ((int)a != 0);  <--- likewise, and comparision
}

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=15017

[Bug optimization/15017] [tree-ssa] compare (equal) with casts are not removed

[dann at godzilla dot ics dot uci dot edu]

------- Additional Comments From dann at godzilla dot ics dot uci dot edu  2004-04-20 15:19 -------
> bar (a)
> {
> <bb 0>:
>   return (int)a;  <-- good code as _Bool is promoted to int by the ABI

I am not so sure about this, the ABI should not matter at the tree level. 

Here is another example:

_Bool A;
_Bool foo01 (void)
{
  if (A)
    return 1;
  else
    return 0;
}

The .original dump is:
      if ((int)A != 0)
         {
            return <return-value> = 1;
         }
      else
         {
            return <return-value> = 0;
         }
The cast should not be emitted here. So IMO the main problem is 
emitting the casts in the first place, not being able to get rid
of them later is a different issue. 


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=15017

[Bug tree-optimization/15017] [tree-ssa] compare (equal) with casts are not removed

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-05-18 03:50 -------
The second example in comment 0 is fixed when the patch in 15459 is applied. 

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=15017

[Bug tree-optimization/15017] [tree-ssa] compare (equal) with casts are not removed

[pinskia at gcc dot gnu dot org]

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=15017

[Bug tree-optimization/15017] [tree-ssa] compare (equal) with casts are not removed

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-06-07 19:33 -------
I will note that at least one of examples later on are filed as PR 15618.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
  BugsThisDependsOn|                            |15618


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=15017

[Bug tree-optimization/15017] [tree-ssa] compare (equal) with casts are not removed

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2005-05-02 04:46 -------
Example 1 in comment #0 has been fixed already.
foo0 and foo1 in comment #3 is PR 15618.
foo, foo2, and foo3 in comment #3 has been already fixed also.

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=15017

[Bug tree-optimization/15017] [tree-ssa] compare (equal) with casts are not removed

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2005-05-02 05:00 -------
Oh, bool_var1 != bool_var0 should be changed to use TRUTH_XOR_EXPR also.

I will look into that tomorrow.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|2005-01-10 15:42:47         |2005-05-02 05:00:30
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=15017

[Bug tree-optimization/15017] [tree-ssa] compare (equal) with casts are not removed

[dann at godzilla dot ics dot uci dot edu]

------- Additional Comments From dann at godzilla dot ics dot uci dot edu  2005-05-02 18:51 -------
Comment #3 in PR15484 has a reference to a patch that might fix the cause for
some of these issues.

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=15017

[Bug tree-optimization/15017] [tree-ssa] compare (equal) with casts are not removed

[pinskia at gcc dot gnu dot org]

-- 
Bug 15017 depends on bug 15618, which changed state.

Bug 15618 Summary: Missed bool optimization
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=15618

           What    |Old Value                   |New Value
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |FIXED

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=15017

[Bug tree-optimization/15017] [tree-ssa] compare (equal) with casts are not removed

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2005-05-08 18:20 -------
I am too busy for this one.

-- 
           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=15017