[Bug rtl-optimization/43491] Unnecessary temporary for global register variable

2011-12-20 Thread amker.cheng at gmail dot com 
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43491

--- Comment #4 from amker.cheng amker.cheng at gmail dot com 2011-12-21 
03:44:03 UTC ---
This bug is even worse on mips.

The cause is ssa-pre eliminates global register variable when it is the RHS of
single assign statment, while following passes do not handle the const/register
attributes of the variable.
It can be handled in tree-ssa-pre.c without hurting true redundancy elimination
on global register variables.

So could somebody change the tag from rtl-optimization to tree-optimization?

[Bug rtl-optimization/43491] Unnecessary temporary for global register variable

2011-11-24 Thread amker.cheng at gmail dot com 
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43491

--- Comment #3 from amker.cheng amker.cheng at gmail dot com 2011-11-24 
09:24:37 UTC ---
(In reply to comment #1)

 
 I'm thinking that this is perfectly normal thing to do, and that the redundant
 move is meant to disappear in a later pass.  My guess is that IRA is choosing
 not to assign the pseudo to r4, but I do not know why at the moment.

As dump in 191r.shed1:
--
(insn 5 7 6 2 (set (reg/f:SI 135 [ reg.0 ])
(reg/v:SI 4 r4 [ reg ])) pr43491.c:16 709 {*thumb2_movsi_insn}
 (expr_list:REG_DEAD (reg/v:SI 4 r4 [ reg ])
(nil)))

(insn 6 5 8 2 (set (reg:SI 137 [ MEM[(unsigned int *)reg.0_12 + 8B] ])
(mem:SI (plus:SI (reg/f:SI 135 [ reg.0 ])
(const_int 8 [0x8])) [2 MEM[(unsigned int *)reg.0_12 + 8B]+0 S4
A32])) pr43491.c:16 709 {*thumb2_movsi_insn}
 (nil))

(jump_insn 8 6 49 2 (parallel [
(set (pc)
(if_then_else (eq (reg:SI 137 [ MEM[(unsigned int *)reg.0_12 +
8B] ])
(const_int 0 [0]))
(label_ref:SI 22)
(pc)))
(clobber (reg:CC 24 cc))
]) pr43491.c:16 747 {*thumb2_cbz}
 (expr_list:REG_DEAD (reg:SI 137 [ MEM[(unsigned int *)reg.0_12 + 8B] ])
(expr_list:REG_UNUSED (reg:CC 24 cc)
(expr_list:REG_BR_PROB (const_int 900 [0x384])
(nil
 - 22)

(code_label 49 8 48 3 4  [1 uses])

(note 48 49 16 3 [bb 3] NOTE_INSN_BASIC_BLOCK)

(note 16 48 14 3 NOTE_INSN_DELETED)

(call_insn 14 16 15 3 (parallel [
(call (mem:SI (symbol_ref:SI (c) [flags 0x41]  function_decl
0xb76c3b80 c) [0 c S4 A32])
(const_int 0 [0]))
(use (const_int 0 [0]))
(clobber (reg:SI 14 lr))
]) pr43491.c:17 247 {*call_symbol}
 (nil)
(nil))

(insn 15 14 17 3 (set (reg:SI 138 [ MEM[(unsigned int *)reg.0_12 + 8B] ])
(mem:SI (plus:SI (reg/f:SI 135 [ reg.0 ])
(const_int 8 [0x8])) [2 MEM[(unsigned int *)reg.0_12 + 8B]+0 S4
A32])) pr43491.c:16 709 {*thumb2_movsi_insn}
 (nil))
--
Since reg is manually declared in r4, function globalize_reg sets r4 in
fixed_reg_set/call_used_reg_set/call_fixed_reg_set. IRA then add r4 into
allocno(r135)'s conflict_hard_regs. That's why IRA not assigns the pseudo(r135)
to r4. I guess it's natural unless we can make IRA aware of constant register.

[Bug rtl-optimization/43491] Unnecessary temporary for global register variable

2011-11-22 Thread amker.cheng at gmail dot com 
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43491

amker.cheng amker.cheng at gmail dot com changed:

   What|Removed |Added

 CC||amker.cheng at gmail dot
   ||com

--- Comment #2 from amker.cheng amker.cheng at gmail dot com 2011-11-23 
05:50:51 UTC ---
Noticed that pass 097t.copyprop4 propagates reg.0_12 to statement Y in
following dump:
-
bb 2:
  reg.0_12 = reg;
  D.4705_13 = MEM[(unsigned int *)reg.0_12 + 8B];   -statement Z
  if (D.4705_13 != 0)
goto bb 3;
  else
goto bb 6;

bb 3:

bb 4:
  c ();
  reg.0_1 = reg.0_12; 
-statement X
  D.4705_3 = MEM[(unsigned int *)reg.0_1 + 8B]; -statement Y
  if (D.4705_3 != 0)
goto bb 5;
  else
goto bb 6;

bb 5:
  goto bb 4;

bb 6:
  return;
-
to be:
  reg.0_1 = reg.0_12;  
-statement X
  D.4705_3 = MEM[(unsigned int *)reg.0_12 + 8B]; -statement Y

So, should it propagates reg directly? Could this be done on ssa?

Also I found 
1) there are similar cases on redundant copy or load constant, for example,
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44025
2) some of these cases are generated after expanding into rtl;
3) redundant copy might be handled in IRA, but redundant load const might be
more difficult.

How about extending regcprop.c pass into a global pass?

[Bug rtl-optimization/43491] Unnecessary temporary for global register variable

2010-09-08 Thread ibolton at gcc dot gnu dot org 


--- Comment #1 from ibolton at gcc dot gnu dot org  2010-09-08 16:21 ---
reg is assigned to a temporary (reg.0) at the very first tree pass, as shown by
this 004t.gimple dump:

d ()
{
  struct b * const reg.0;
  unsigned int * D.2019;
  int D.2020;

  goto D.1276;
  D.1275:
  c ();
  D.1276:
  reg.0 = reg;
  D.2019 = reg.0-j;
  D.2020 = diff (D.2019);
  if (D.2020 != 0) goto D.1275; else goto D.1277;
  D.1277:
}

I'm thinking that this is perfectly normal thing to do, and that the redundant
move is meant to disappear in a later pass.  My guess is that IRA is choosing
not to assign the pseudo to r4, but I do not know why at the moment.


-- 

ibolton at gcc dot gnu dot org changed:

   What|Removed |Added

 Status|UNCONFIRMED |NEW
 Ever Confirmed|0   |1
   Keywords||missed-optimization, ra
  Known to fail||4.5.3 4.6.0
   Last reconfirmed|-00-00 00:00:00 |2010-09-08 16:21:50
   date||


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43491