[Bug middle-end/42505] [4.4/4.5/4.6 Regression] loop canonicalization causes a lot of unnecessary temporary variables

[Bug middle-end/42505] [4.4/4.5/4.6 Regression] loop canonicalization causes a lot of unnecessary temporary variables

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42505

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.4.5                       |4.4.6

[Bug middle-end/42505] [4.4/4.5/4.6 Regression] loop canonicalization causes a lot of unnecessary temporary variables

[sandra at codesourcery dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42505

--- Comment #13 from Sandra Loosemore <sandra at codesourcery dot com> 2010-10-01 15:01:08 UTC ---
I think this bug is fixed now.

[Bug middle-end/42505] [4.4/4.5/4.6 Regression] loop canonicalization causes a lot of unnecessary temporary variables

[law at redhat dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42505

Jeffrey A. Law <law at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |law at redhat dot com
         Resolution|                            |FIXED
      Known to fail|                            |

--- Comment #14 from Jeffrey A. Law <law at redhat dot com> 2011-01-13 15:45:22 UTC ---
Fixed long ago.

[Bug middle-end/42505] [4.4/4.5/4.6 Regression] loop canonicalization causes a lot of unnecessary temporary variables

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42505

Richard Guenther <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to work|                            |4.6.0
   Target Milestone|4.4.6                       |4.6.0

--- Comment #15 from Richard Guenther <rguenth at gcc dot gnu.org> 2011-01-13 16:47:22 UTC ---
For 4.6.  Nothing to backport here.

[Bug middle-end/42505] [4.4/4.5/4.6 Regression] loop canonicalization causes a lot of unnecessary temporary variables

[sandra at gcc dot gnu dot org]

------- Comment #12 from sandra at gcc dot gnu dot org  2010-07-10 18:43 -------
Subject: Bug 42505

Author: sandra
Date: Sat Jul 10 18:43:29 2010
New Revision: 162043

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=162043
Log:
2010-07-10  Sandra Loosemore  <sandra@codesourcery.com>

        PR middle-end/42505

        gcc/
        * tree-inline.c (estimate_num_insns): Refactor builtin complexity
        lookup code into....
        * builtins.c (is_simple_builtin, is_inexpensive_builtin): ...these
        new functions.
        * tree.h (is_simple_builtin, is_inexpensive_builtin): Declare.
        * cfgloopanal.c (target_clobbered_regs): Define.
        (init_set_costs): Initialize target_clobbered_regs.
        (estimate_reg_pressure_cost): Add call_p argument.  When true,
        adjust the number of available registers to exclude the
        call-clobbered registers.
        * cfgloop.h (target_clobbered_regs): Declare.
        (estimate_reg_pressure_cost): Adjust declaration.
        * tree-ssa-loop-ivopts.c (struct ivopts_data): Add body_includes_call.
        (ivopts_global_cost_for_size): Pass it to estimate_reg_pressure_cost.
        (determine_set_costs): Dump target_clobbered_regs.
        (loop_body_includes_call): New function.
        (tree_ssa_iv_optimize_loop): Use it to initialize new field.
        * loop-invariant.c (gain_for_invariant): Adjust arguments to pass
        call_p flag through.
        (best_gain_for_invariant): Likewise.
        (find_invariants_to_move): Likewise.
        (move_single_loop_invariants): Likewise, using already-computed
        has_call field.

Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/builtins.c
    trunk/gcc/cfgloop.h
    trunk/gcc/cfgloopanal.c
    trunk/gcc/loop-invariant.c
    trunk/gcc/tree-inline.c
    trunk/gcc/tree-ssa-loop-ivopts.c
    trunk/gcc/tree.h


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42505

[Bug middle-end/42505] [4.4/4.5/4.6 Regression] loop canonicalization causes a lot of unnecessary temporary variables

[sandra at gcc dot gnu dot org]

------- Comment #11 from sandra at gcc dot gnu dot org  2010-07-05 17:41 -------
Subject: Bug 42505

Author: sandra
Date: Mon Jul  5 17:40:57 2010
New Revision: 161844

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=161844
Log:
2010-07-05  Sandra Loosemore  <sandra@codesourcery.com>

        PR middle-end/42505

        gcc/
        * tree-ssa-loop-ivopts.c (determine_set_costs): Delete obsolete
        comments about cost model.
        (try_add_cand_for):  Add second strategy for choosing initial set
        based on original IVs, controlled by ORIGINALP argument.
        (get_initial_solution): Add ORIGINALP argument.
        (find_optimal_iv_set_1): New function, split from find_optimal_iv_set.
        (find_optimal_iv_set): Try two different strategies for choosing
        the IV set, and return the one with lower cost.

        gcc/testsuite/
        * gcc.target/arm/pr42505.c: New test case.

Added:
    trunk/gcc/testsuite/gcc.target/arm/pr42505.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/tree-ssa-loop-ivopts.c


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42505

[Bug middle-end/42505] [4.4/4.5/4.6 Regression] loop canonicalization causes a lot of unnecessary temporary variables

[sandra at codesourcery dot com]

------- Comment #10 from sandra at codesourcery dot com  2010-06-19 12:56 -------
Patch posted here:

http://gcc.gnu.org/ml/gcc-patches/2010-06/msg01920.html


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42505

[Bug middle-end/42505] [4.4/4.5/4.6 Regression] loop canonicalization causes a lot of unnecessary temporary variables

[sandra at codesourcery dot com]

------- Comment #9 from sandra at codesourcery dot com  2010-06-12 07:42 -------
I now have a specific theory of what is going on here.  There are two problems:

(1) estimate_reg_pressure_cost is not accounting for the function call in the
loop body.  In this case it ought to use call_used_regs instead of fixed_regs
to determine how many registers are available for loop invariants.  Here the
target is Thumb-1 and there are only 4 non-call-clobbered registers available
rather than 9, so we are much more constrained than ivopts thinks we are.  This
is pretty straightforward to fix.

(2) For the test case filed with the issue, there are 4 registers needed for
the two candidates and two invariants ivopts is selecting, so even with the fix
for (1) ivopts thinks it has enough registers available.  But, there are two
uses of the form (src + offset) in the ivopts output, although they appear
differently in the gimple code.  RTL optimizations are combining these and
allocating a temporary.  Since the two uses span the function call in the loop
body, the temporary needs to be assigned to a non-call-clobbered register. 
This is why there is a spill of the other loop invariant.  Perhaps we could
make the RA smarter about recomputing the src + offset value rather than resort
to spilling something, but since I am dumb about the RA ;-) I'm planning to
keep poking at the ivopts cost model instead.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42505

[Bug middle-end/42505] [4.4/4.5/4.6 Regression] loop canonicalization causes a lot of unnecessary temporary variables

[sandra at codesourcery dot com]

------- Comment #8 from sandra at codesourcery dot com  2010-06-10 13:01 -------
I was barking up the wrong tree with my last idea -- the signed/unsigned
conversion business was a red herring.  Here's what I now believe is the
problem: the costs computation is underestimating the register pressure costs
so that we are in fact spilling when the cost computation thinks it still has
"free" registers.

A hack to make get_computation_cost_at add target_reg_cost to the result when
it must use a scratch register seemed to have positive overall effects on code
size (as well as fixing the test case).  But, I don't think that's the real
solution, as I can't come up with a good logical justification for putting such
a cost there.  :-)  estimate_reg_pressure_cost already reserves 3 "free"
registers for such things.  Anyway, I am continuing to poke at this in hopes of
figuring out where the register costs model is really going wrong.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42505

[Bug middle-end/42505] [4.4/4.5/4.6 Regression] loop canonicalization causes a lot of unnecessary temporary variables

[sandra at codesourcery dot com]

------- Comment #7 from sandra at codesourcery dot com  2010-06-05 20:41 -------
OK, I'm testing a hack to rewrite_use_compare to make it know that it doesn't
have to introduce a temporary just to compare against constant zero.  I'm also
doing a little tuning of the costs model for -Os, using CSiBE.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42505

[Bug middle-end/42505] [4.4/4.5/4.6 Regression] loop canonicalization causes a lot of unnecessary temporary variables

[rguenth at gcc dot gnu dot org]

------- Comment #6 from rguenth at gcc dot gnu dot org  2010-06-04 09:08 -------
If the result of the conversion is only used in an exit equality test against a
constant it can be dropped.  This could also happen in a following
forwprop run which is our single tree-combiner (though that currently will
combine into comparisons only if the result will be a constant, it doesn't
treat defs with a single use specially which it could, if the combined
constant is in gimple form).


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42505

[Bug middle-end/42505] [4.4/4.5/4.6 Regression] loop canonicalization causes a lot of unnecessary temporary variables

[steven at gcc dot gnu dot org]

------- Comment #5 from steven at gcc dot gnu dot org  2010-06-04 07:45 -------
AFAIU, you can't randomly change signed to unsigned, due to different overflow
semantics, which is why IVOPTS doesn't make this change itself. Imagine you
enter the loop with count = 0, and with a second counter hidden in func. You
will not get the same number of iterations if you change the type of count from
"int" to "unsigned int".


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42505

[Bug middle-end/42505] [4.4/4.5/4.6 Regression] loop canonicalization causes a lot of unnecessary temporary variables

[sandra at codesourcery dot com]

------- Comment #4 from sandra at codesourcery dot com  2010-06-04 00:09 -------
I've been looking at this problem today.  Here's the stupid part coming out of
ivopts:

<bb 5>:
  # ivtmp.7_21 = PHI <0(2), ivtmp.7_20(4)>
  # ivtmp.10_22 = PHI <ivtmp.10_24(2), ivtmp.10_23(4)>
  count_25 = (int) ivtmp.10_22;
  if (count_25 != 0)
    goto <bb 3>;
  else
    goto <bb 6>;

No subsequent pass is recognizing that the unsigned-to-signed conversion is
useless and "count" is otherwise dead.  

If I change the parameter "count" to have type "unsigned int", then ivopts does
the obvious replacement itself:

<bb 5>:
  # ivtmp.7_21 = PHI <0(2), ivtmp.7_20(4)>
  # ivtmp.10_22 = PHI <count_7(D)(2), ivtmp.10_23(4)>
  if (ivtmp.10_22 != 0)
    goto <bb 3>;
  else
    goto <bb 6>;

Then "count" is completely gone from the loop after ivopts and the resulting
code looks good.

So, fix this somewhere inside ivopts to make the signed case produce the same
code as the unsigned one?  Or tell it not to replace count at all if it has to
do a type conversion?  I'm still trying to find my way around the code for this
pass to figure out where things happen, so if this is obvious to someone else
I'd appreciate a pointer.  :-)


-- 

sandra at codesourcery dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |sandra at codesourcery dot
                   |                            |com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42505

[Bug middle-end/42505] [4.4/4.5/4.6 Regression] loop canonicalization causes a lot of unnecessary temporary variables

[jakub at gcc dot gnu dot org]

-- 

jakub at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.4.4                       |4.4.5


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42505