[Bug middle-end/21082] New: &a[b] - &a[c] is not folded to b - c

[Bug middle-end/21082] New: &a[b] - &a[c] is not folded to b - c

[pinskia at gcc dot gnu dot org]

The following C++ code is not fully as optimizated as the C version:
typedef __SIZE_TYPE__ size_t;
size_t a[100];
size_t f(size_t b, size_t c)
{
  return &a[b] - &a[c];
}

Found this while looking into the tree dump for mgrid.

-- 
           Summary: &a[b] - &a[c] is not folded to b - c
           Product: gcc
           Version: 4.1.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: enhancement
          Priority: P2
         Component: middle-end
        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=21082

[Bug middle-end/21082] &a[b] - &a[c] is not folded to b - c

[pinskia at gcc dot gnu dot org]

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
OtherBugsDependingO|                            |19987
              nThis|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21082

[Bug middle-end/21082] &a[b] - &a[c] is not folded to b - c

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2005-04-18 03:19 -------
This should improve mgrid and IV selection.

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21082

[Bug middle-end/21082] &a[b] - &a[c] is not folded to b - c

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2005-04-18 04:06 -------
The code in comment #0 should produce no multiply/divides/shifts but does currently (again with the 
C++ front-end).
Take the following code:
typedef __SIZE_TYPE__ size_t;
size_t a[100];
size_t f(size_t b, size_t c)
{
  return (&a[b] - &a[c])*sizeof(*a);
}
We get the good code but only after combine so this blocks both the generic one and the RTL based 
missed fold optimizators and we can add the TREE keyword too for the above testcase.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
OtherBugsDependingO|                            |19986
              nThis|                            |
           Keywords|                            |TREE


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21082

[Bug middle-end/21082] &a[b] - &a[c] is not folded to b - c

[phython at gcc dot gnu dot org]

------- Additional Comments From phython at gcc dot gnu dot org  2005-04-19 14:57 -------
 Yup, the dumps from the c++ front end is:
;; Function size_t f(size_t, size_t) (_Z1fjj)

size_t f(size_t, size_t) (b, c)
{
<bb 0>:
  return (size_t) (((int) &a[b] - (int) &a[c]) /[ex] 4);

}

 and the C front-end dump is:
;; Function f (f)

f (b, c)
{
<bb 0>:
  return (size_t) (b - c);

}


-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|                            |1
   Last reconfirmed|0000-00-00 00:00:00         |2005-04-19 14:57:39
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21082

[Bug middle-end/21082] &a[b] - &a[c] is not folded to b - c

[rguenth at gcc dot gnu dot org]

------- Additional Comments From rguenth at gcc dot gnu dot org  2005-04-23 14:31 -------
PR19807 is related.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
OtherBugsDependingO|                            |19807
              nThis|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21082

[Bug middle-end/21082] &a[b] - &a[c] is not folded to b - c

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2005-04-23 16:24 -------
Zdenek was complaining about this in:
 <http://gcc.gnu.org/ml/gcc-patches/2005-04/msg02411.html>.

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21082

[Bug middle-end/21082] &a[b] - &a[c] is not folded to b - c

[rguenth at gcc dot gnu dot org]

------- Additional Comments From rguenth at gcc dot gnu dot org  2005-04-23 21:05 -------
Patch at
http://gcc.gnu.org/ml/gcc-patches/2005-04/msg02499.html

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |rguenth at gcc dot gnu dot
                   |dot org                     |org
                URL|                            |http://gcc.gnu.org/ml/gcc-
                   |                            |patches/2005-
                   |                            |04/msg02499.html
             Status|NEW                         |ASSIGNED
           Keywords|                            |patch
   Last reconfirmed|2005-04-19 14:57:39         |2005-04-23 21:05:50
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21082

[Bug middle-end/21082] &a[b] - &a[c] is not folded to b - c

[cvs-commit at gcc dot gnu dot org]

------- Additional Comments From cvs-commit at gcc dot gnu dot org  2005-04-23 21:34 -------
Subject: Bug 21082

CVSROOT:	/cvs/gcc
Module name:	gcc
Changes by:	rguenth@gcc.gnu.org	2005-04-23 21:34:42

Modified files:
	gcc            : ChangeLog fold-const.c 
	gcc/testsuite  : ChangeLog 
Added files:
	gcc/testsuite/g++.dg/tree-ssa: pr21082.C 

Log message:
	2005-04-23  Richard Guenther  <rguenth@gcc.gnu.org>
	
	PR middle-end/21082
	* fold-const.c: Fold &a[i]-&a[j] to i-j.
	
	* g++.dg/tree-ssa/pr21082.C: New testcase.

Patches:
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/ChangeLog.diff?cvsroot=gcc&r1=2.8430&r2=2.8431
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/fold-const.c.diff?cvsroot=gcc&r1=1.569&r2=1.570
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/testsuite/ChangeLog.diff?cvsroot=gcc&r1=1.5388&r2=1.5389
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/testsuite/g++.dg/tree-ssa/pr21082.C.diff?cvsroot=gcc&r1=NONE&r2=1.1



-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21082

[Bug middle-end/21082] &a[b] - &a[c] is not folded to b - c

[rguenth at gcc dot gnu dot org]

------- Additional Comments From rguenth at gcc dot gnu dot org  2005-04-23 21:36 -------
Fixed.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |FIXED


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21082

[Bug middle-end/21082] &a[b] - &a[c] is not folded to b - c

[pinskia at gcc dot gnu dot org]

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |4.1.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21082