[Bug tree-optimization/94846] Failure to optimize jnc+inc into adc

2021-09-04 Thread pinskia at gcc dot gnu.org via Gcc-bugs 
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94846

Andrew Pinski  changed:

   What|Removed |Added

   Severity|normal  |enhancement

--- Comment #5 from Andrew Pinski  ---
After r12-897 (which added a late sink pass), we get the following in
.optimized:
  if (_10 != 0)
goto ; [50.00%]
  else
goto ; [50.00%]

   [local count: 536870913]:
  _2 = _1 + 1;

   [local count: 1073741824]:
  # prephitmp_11 = PHI <_1(2), _2(3)>
  # _13 = PHI <_1(2), _2(3)>
  *p_5(D) = _13;
  return prephitmp_11;

Notice how prephitmp_11 and _13 are the same but no RTL optimizers handles
that.

[Bug tree-optimization/94846] Failure to optimize jnc+inc into adc

2020-11-26 Thread rguenth at gcc dot gnu.org via Gcc-bugs 
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94846

Richard Biener  changed:

   What|Removed |Added

 Status|NEW |ASSIGNED
   Assignee|unassigned at gcc dot gnu.org  |rguenth at gcc dot 
gnu.org

--- Comment #4 from Richard Biener  ---
The sinking opportunity is a secondary one, sink does

Sinking # .MEM_8 = VDEF <.MEM_4(D)>
*p_5(D) = _1;
 from bb 2 to bb 5

but then not sinking further with the store commoning I implemented for GCC 11.

   [local count: 1073741824]:
  u_6 = *p_5(D);
  _1 = u_6 + x_7(D);
  if (_1 < u_6)
goto ; [50.00%]
  else
goto ; [50.00%]

   [local count: 536870912]:
  *p_5(D) = _1;
  goto ; [100.00%]

   [local count: 536870913]:
  _2 = _1 + 1;
  *p_5(D) = _2;

   [local count: 1073741824]:
  # prephitmp_11 = PHI <_1(5), _2(3)>
  return prephitmp_11;

regular sinking works up the postdom tree.  In reality we'd have to iterate
sinking and commoning as can be seen here given we're lazy and not computing
a combined dataflow.

[Bug tree-optimization/94846] Failure to optimize jnc+inc into adc

2020-11-25 Thread ubizjak at gmail dot com via Gcc-bugs 
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94846

Uroš Bizjak  changed:

   What|Removed |Added

 Ever confirmed|0   |1
   Last reconfirmed||2020-11-25
 Status|UNCONFIRMED |NEW
 CC||rguenth at gcc dot gnu.org
  Component|rtl-optimization|tree-optimization

--- Comment #3 from Uroš Bizjak  ---
This looks like a tree-optimization problem. A store to *p_5(D) could sink all
the way to bb5. RTL gets expanded from:

  ...
  if (_10 != 0)
goto ; [50.00%]
  else
goto ; [50.00%]

   [local count: 536870912]:
  *p_5(D) = _1;
  goto ; [100.00%]

   [local count: 536870913]:
  _2 = _1 + 1;
  *p_5(D) = _2;

   [local count: 1073741824]:
  # prephitmp_11 = PHI <_1(3), _2(4)>
  return prephitmp_11;

ifcvt RTL pass (_.ce1) is unable to convert:

   ...
   17: r86:SI=r89:SI
  REG_DEAD r89:SI
   18: flags:CCZ=cmp(r85:SI,0)
  REG_DEAD r85:SI
   19: pc={(flags:CCZ!=0)?L24:pc}
  REG_DEAD flags:CCZ
  REG_BR_PROB 536870916
   20: NOTE_INSN_BASIC_BLOCK 5
   21: [r87:DI]=r89:SI
  REG_DEAD r87:DI
  ; pc falls through to BB 7
   24: L24:
   25: NOTE_INSN_BASIC_BLOCK 6
   26: {r86:SI=r89:SI+0x1;clobber flags:CC;}
  REG_UNUSED flags:CC
   27: [r87:DI]=r86:SI
  REG_DEAD r87:DI
   32: L32:
   35: NOTE_INSN_BASIC_BLOCK 7
   ...


IF-THEN-ELSE-JOIN block found, pass 2, test 2, then 5, else 6, join 7

===

In case p is not a pointer, RTL optimizers start with:

  ...
  if (_8 != 0)
goto ; [50.00%]
  else
goto ; [50.00%]

   [local count: 536870913]:
  p_5 = p_4 + 1;

   [local count: 1073741824]:
  # p_1 = PHI 
  return p_1;

and RTL ifcvt pass is able to convert this form to addcc:

IF-THEN-JOIN block found, pass 2, test 2, then 5, join 6

if-conversion succeeded through noce_try_addcc