[Bug tree-optimization/98673] New: pass fre4 inhibit pass dom3 to create much more optimized code

["rjiejie at me dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98673

            Bug ID: 98673
           Summary: pass fre4 inhibit pass dom3 to create much more
                    optimized code
           Product: gcc
           Version: 10.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: rjiejie at me dot com
  Target Milestone: ---

Created attachment 49962
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=49962&action=edit
bug test file

a, compiler option:

cc1 -mabi=lp64d -march=rv64gc -O2 -S

b, hot code in function t_run_test:

        j       .L30
.L39:
        mv      a4,a3
.L30:
        ld      a2,8(a5)
        addi    a3,a4,1
        slli    t3,a4,3
        ble     a2,a1,.L28
        ld      t5,0(a5)
        bge     a1,t5,.L50
.L28:
        addi    a5,a5,8
        bne     a3,a0,.L39    : hot code loop to .L39

better code in version 8.4 with same compiler option:
=====================================================

.L30:
        ld      t1,8(a4)
        slli    a7,a5,3
        ble     t1,a3,.L28
        ld      t4,0(a4)
        bge     a3,t4,.L50
.L28:
        addi    a5,a5,1
        addi    a4,a4,8
        bne     a5,t3,.L30    : hot code loop to .L30

v10.2.0 gcc has more one instruction than v8.4.0.

analize gcc pass of source code in v10.2.0:
===========================================

before pass fr4:
----------------

<bb 8> [local count: 82176881]:
  engLoad.11_20 = engLoad;
  loadValue.13_26 = loadValue;
  _410 = (unsigned long) numXEntries.17_218;
  _409 = _410 + 18446744073709551615;
  _408 = (long int) _409;

... ...

<bb 12> [local count: 986782143]:
  i1_174 = i1_6 + 1;
  if (i1_174 != _408)
    goto <bb 9>; [94.50%]
  else
    goto <bb 13>; [5.50%]

  <bb 13> [local count: 54273018]:
  # i1_420 = PHI <i1_174(12)>
  _433 = (long unsigned int) i1_420;
  _434 = _433 + 1;
  _435 = _434 * 8;
  _436 = i1_420 + 1;
  _440 = _435 - 8;
  _442 = engLoad.11_20 + _440;
  goto <bb 15>; [100.00%]

after pass fr4:
---------------

<bb 8> [local count: 82176881]:
engLoad.11_20 = engLoad;
loadValue.13_26 = loadValue;
_410 = (unsigned long) numXEntries.17_218;
_409 = _410 + 18446744073709551615;

... ...

<bb 12> [local count: 986782143]:
  i1_174 = i1_6 + 1;
  if (i1_174 != _213)
    goto <bb 9>; [94.50%]
  else
    goto <bb 13>; [5.50%]

<bb 13> [local count: 54273018]:
_433 = (long unsigned int) i1_174;
_434 = _433 + 1;
_435 = _434 * 8;
_436 = i1_174 + 1;
_440 = _435 - 8;
_442 = engLoad.11_20 + _440;
goto <bb 15>; [100.00%]

pass fr4 remove 'Removing dead stmt _408 = (long int) _409;',
pass dom3 can't optimize this <bb 13> about '_433 = (long unsigned int)
i1_174;'

if <bb 13> use i1_174 node same as <bb 12>, so that conflict will be happened
in pass expand on processing coalesced ssa/phi nodes, and then will split edge.


need help ....:)