[Bug regression/20372] New: Reversed branch-on-count loop (DoLoop)

[Bug regression/20372] New: Reversed branch-on-count loop (DoLoop)

[pthaugen at us dot ibm dot com]

Noticed a regression relative to 4.0 on the code generated for one of the loops
in zaxpy.f of the SPEC wupwise benchark. The loop is transformed into a
branch-on-count loop, but the target on the branch is the loop exit (return in
this case) instead of the loop start. The 'bct' is immediately followed by an
unconditional branch to the loop start.

Here's a snippet of the generated code (this is for the first loop in the
source, even though it appears as the second loop in the generated code). 'L18'
is the epilog block.

.L15:

	addi %r0,%r7,-1	 # D.511, ix,
        ...
        ...
	stfdx %f11,%r11,%r31	 # (* zy), SR.12
	bdz .L18
	b .L15

-- 
           Summary: Reversed branch-on-count loop (DoLoop)
           Product: gcc
           Version: 4.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: regression
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: pthaugen at us dot ibm dot com
                CC: gcc-bugs at gcc dot gnu dot org
 GCC build triplet: powerpc*-*-*
  GCC host triplet: powerpc*-*-*
GCC target triplet: powerpc*-*-*


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20372

[Bug regression/20372] Reversed branch-on-count loop (DoLoop)

[pthaugen at us dot ibm dot com]

------- Additional Comments From pthaugen at us dot ibm dot com  2005-03-07 21:59 -------
Created an attachment (id=8357)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=8357&action=view)
Source file


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20372

[Bug rtl-optimization/20372] Reversed branch-on-count loop (DoLoop)

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2005-03-07 22:04 -------
I saw this too for some C code somewhere (but that was not a regression at least as far as I could see).

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |pinskia at gcc dot gnu dot
                   |                            |org
          Component|regression                  |rtl-optimization
           Keywords|                            |missed-optimization


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20372

[Bug rtl-optimization/20372] [4.0/4.1 Regression] Reversed branch-on-count loop (DoLoop)

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2005-03-07 22:19 -------
Here is a simplified C code which shows the problem:
int *ggg;
void f(int l1, int l2)
{
  int i;
  if (l1)
  {
    for(i=0;i<l1;i++)
     ggg[i]=1;
   return;
  }
  for(i=0;i<l2;i++)
   ggg[i]=i;
}

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|                            |1
      Known to fail|                            |4.0.0 4.1.0
      Known to work|                            |3.3.3
   Last reconfirmed|0000-00-00 00:00:00         |2005-03-07 22:19:07
               date|                            |
            Summary|Reversed branch-on-count    |[4.0/4.1 Regression]
                   |loop (DoLoop)               |Reversed branch-on-count
                   |                            |loop (DoLoop)
   Target Milestone|---                         |4.0.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20372

[Bug rtl-optimization/20372] [4.0 Regression] Reversed branch-on-count loop (DoLoop)

[dje at gcc dot gnu dot org]

------- Additional Comments From dje at gcc dot gnu dot org  2005-03-09 20:32 -------
Joern's patch fixes the regression on mainline.
http://gcc.gnu.org/ml/gcc-patches/2005-03/msg00777.html

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to fail|4.0.0 4.1.0                 |4.0.0
            Summary|[4.0/4.1 Regression]        |[4.0 Regression] Reversed
                   |Reversed branch-on-count    |branch-on-count loop
                   |loop (DoLoop)               |(DoLoop)


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20372

[Bug rtl-optimization/20372] [4.0 Regression] Reversed branch-on-count loop (DoLoop)

[giovannibajo at libero dot it]

------- Additional Comments From giovannibajo at libero dot it  2005-03-09 20:50 -------
can the same patch be applied to 4.0 branch as well?

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |sayle at gcc dot gnu dot
                   |                            |org, amylaar at gcc dot gnu
                   |                            |dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20372

[Bug rtl-optimization/20372] [4.0 Regression] Reversed branch-on-count loop (DoLoop)

[pthaugen at us dot ibm dot com]

------- Additional Comments From pthaugen at us dot ibm dot com  2005-03-09 20:55 -------
I only noticed the regression on 4.1, things look fine to me on 4.0 (for both
zaxpy.f and Andrew's C example).


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20372

[Bug rtl-optimization/20372] [4.1 Regression] Reversed branch-on-count loop (DoLoop)

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2005-03-09 22:41 -------
Hmm, I thought I tested 4.0.0, I must have messed up. so closing as fixed.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
      Known to fail|4.0.0                       |
      Known to work|3.3.3                       |3.3.3 4.0.0
         Resolution|                            |FIXED
            Summary|[4.0 Regression] Reversed   |[4.1 Regression] Reversed
                   |branch-on-count loop        |branch-on-count loop
                   |(DoLoop)                    |(DoLoop)
   Target Milestone|4.0.0                       |4.1.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20372