[Bug rtl-optimization/37471] New: Move invariant pulls too many cmps out of a loop

[Bug rtl-optimization/37471] New: Move invariant pulls too many cmps out of a loop

[pinskia at gcc dot gnu dot org]

I was looking at some code generation for an internal benchmark when I noticed
this.  With the current trunk on powerpc, we get a mfcr which is slow for the
cell (and most likely other PPCs too) as we pulled too many cmps with some
loops.
A simple example:
int f(int b, int l, int d, int c, int e)
{
  int i = 0;

  for(i = 0;i< l;i ++)
  {
    if (b)
      g();
    if (c)
      g();
    if (d)
      g();
    if (e)
      g();
  }
}


-- 
           Summary: Move invariant pulls too many cmps out of a loop
           Product: gcc
           Version: 4.4.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: normal
          Priority: P3
         Component: rtl-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: pinskia at gcc dot gnu dot org
GCC target triplet: powerpc*-*-*


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37471

[Bug rtl-optimization/37471] Move invariant pulls too many cmps out of a loop

[pinskia at gcc dot gnu dot org]

------- Comment #1 from pinskia at gcc dot gnu dot org  2008-09-14 04:42 -------
Note this is not a regression as loop.c did the same.


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to fail|                            |4.0.0 3.4.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37471

[Bug rtl-optimization/37471] Move invariant pulls too many cmps out of a loop

[pinskia at gcc dot gnu dot org]

------- Comment #2 from pinskia at gcc dot gnu dot org  2008-09-21 00:32 -------
While looking a different bug dealing with invariant motion, I noticed that
estimate_reg_pressure_cost does not take into account the mode of the new
register.  This seems like a big issue.  Also init_set_costs always uses SImode
which is not a good representation of the register pressure in general.  


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37471

[Bug rtl-optimization/37471] Move invariant pulls too many cmps out of a loop

[pinskia at gcc dot gnu dot org]

------- Comment #3 from pinskia at gcc dot gnu dot org  2010-03-02 18:53 -------
Still happens on the trunk.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37471

[Bug rtl-optimization/37471] Move invariant pulls too many cmps out of a loop

[steven at gcc dot gnu dot org]

------- Comment #4 from steven at gcc dot gnu dot org  2010-03-02 21:58 -------
Can you post the output .s of gcc, and the .s you expect?


-- 

steven at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |WAITING


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37471

[Bug rtl-optimization/37471] Move invariant pulls too many cmps out of a loop

[pinskia at gcc dot gnu dot org]

------- Comment #5 from pinskia at gcc dot gnu dot org  2010-03-02 22:02 -------
It is pretty obvious from doing a cross build.  We get a couple sets of:
        lwz 0,112(1)
        rlwinm 0,0,4,0xffffffff
        mtcrf 1,0
        rlwinm 0,0,28,0xffffffff
        beq 7,.L6

Which loads r0 from the stack and then puts it into a conditional register and
the branches.  Note the rlwinm's are there to shift the registers around to put
it into the correct location for the mtcrf.


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|WAITING                     |UNCONFIRMED


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37471

[Bug rtl-optimization/37471] Move invariant pulls too many cmps out of a loop

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=37471

--- Comment #7 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
I Notice LLVM does similarly on this testcase too.

[Bug rtl-optimization/37471] Move invariant pulls too many cmps out of a loop

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=37471

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|normal                      |enhancement
   Last reconfirmed|2015-11-22 00:00:00         |2021-12-18