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From: "amker.cheng at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug bootstrap/59536] [4.9 regression] internal compiler error: in cselib_record_set, at cselib.c:2376 breaks m68k-linux bootstrap
Date: Thu, 19 Dec 2013 08:27:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59536

--- Comment #10 from bin.cheng <amker.cheng at gmail dot com> ---
The offending loop before IVOPT is like:

  <bb 350>:
  # var_index_1889 = PHI <1(924), var_index_983(923)>
  # var_index.250_1269 = PHI <1(924), var_index.250_1959(923)>
  if (var_index.250_1269 < _1237)
    goto <bb 351>;
  else
    goto <bb 885>;

  <bb 351>:
  loopi_952 = MEM[(const struct vec
*)pretmp_2270].m_vecdata[var_index.250_1269];
  _947 = loopi_952->num;
  if (_947 == pretmp_2268)
    goto <bb 352>;
  else
    goto <bb 923>;

  <bb 923>:
  var_index_983 = var_index_1889 + 1;
  var_index.250_1959 = (unsigned int) var_index_983;
  goto <bb 350>;

  <bb 924>:
  goto <bb 350>;

The patch can recognize var_index.250_1269 is an iv with {1, 1}_loop, thus
rewriting the loop into:


  <bb 350>:
  # var_index_1889 = PHI <1(924), var_index_983(923)>
  # ivtmp.1067_1968 = PHI <ivtmp.1067_696(924), ivtmp.1067_884(923)>
  var_index.250_1269 = (unsigned int) var_index_1889;
  if (var_index_1889 != _958)
    goto <bb 351>;
  else
    goto <bb 885>;

  <bb 351>:
  _111 = (void *) ivtmp.1067_1968;
  loopi_952 = MEM[base: _111, offset: 0B];
  ivtmp.1067_884 = ivtmp.1067_1968 + 4;
  _947 = loopi_952->num;
  if (_947 == pretmp_2268)
    goto <bb 352>;
  else
    goto <bb 923>;

  <bb 923>:
  var_index_983 = var_index_1889 + 1;
  goto <bb 350>;

  <bb 924>:
  _1542 = pretmp_2270 + 12;
  ivtmp.1067_696 = (unsigned int) _1542;
  _958 = (int) _1237;
  goto <bb 350>;

The transformation looks good and takes advantage of post-increment addressing
mode for memory access "MEM[base: _111, offset: 0B]".
The loop is expanded into rtl like:
 4438: L4438:
 1814: NOTE_INSN_BASIC_BLOCK 352
 1815: r626:SI=r817:SI
 1816: cc0=cmp(r817:SI,r492:SI)
 1817: pc={(cc0==0)?L4244:pc}
      REG_BR_PROB 900
 1818: NOTE_INSN_BASIC_BLOCK 353
 1819: r490:SI=[r829:SI]
 1820: r829:SI=r829:SI+0x4
 1821: cc0=cmp([r490:SI],r864:SI)
 1822: pc={(cc0!=0)?L4435:pc}
       ...
 4435: L4435:
 4436: NOTE_INSN_BASIC_BLOCK 952
 4437: r817:SI=r817:SI+0x1
 4439: pc=L4438
 4440: barrier
 4441: L4441:
 4442: NOTE_INSN_BASIC_BLOCK 953
 4443: r829:SI=r865:SI+0xc
 4444: r492:SI=r621:SI
   44: r817:SI=0x1
 4445: pc=L4438

Then instruction 1819/1820 are combined by auto-inc-dec pass into:

 1819: r490:SI=[r829:SI++]
      REG_INC r829:SI
 1821: cc0=cmp([r490:SI],r864:SI)
      REG_DEAD r490:SI
 1822: pc={(cc0!=0)?L4435:pc}
      REG_BR_PROB 9550

Problem comes from reload which puts both r490 and r829 into %a0 (reg 8?) and
generates below code:
 1819: %a0:SI=[%a0:SI++]
      REG_INC %a0:SI
 1821: cc0=cmp([%a0:SI],%d2:SI)
 1822: pc={(cc0!=0)?L4435:pc}
      REG_BR_PROB 9550

Insn 1819 is now bogus and causes assertion in cselib.

In IRA, there are dumps like:
      Popping a1119(r829,l0: a921(r829,l17))  -- assign reg 8
      Popping a1122(r1111,l0: a924(r1111,l17))  -- assign reg 8
      Popping a1120(r494,l0: a922(r494,l17))  -- assign reg 9
      Popping a1147(r1054,l0: a1006(r1054,l15))  -- assign reg 8
      Popping a1157(r490,l0: a1124(r490,l17: a959(r490,l18)))  -- assign reg 2

But in reload, there are dumps:

Reloads for insn # 1819
Reload 0: reload_in (SI) = (post_inc:SI (reg:SI 829 [ ivtmp.1067 ]))
    reload_out (SI) = (post_inc:SI (reg:SI 829 [ ivtmp.1067 ]))
    ADDR_REGS, RELOAD_FOR_OPERAND_ADDRESS (opnum = 1), inc by 4
    reload_in_reg: (post_inc:SI (reg:SI 829 [ ivtmp.1067 ]))
    reload_reg_rtx: (reg:SI 8 %a0)
Reload 1: reload_out (SI) = (reg/v/f:SI 490 [ loopi ])
    GENERAL_REGS, RELOAD_FOR_OUTPUT (opnum = 0), optional
    reload_out_reg: (reg/v/f:SI 490 [ loopi ])
Reload 2: reload_in (SI) = (mem/f:SI (post_inc:SI (reg:SI 829 [ ivtmp.1067 ]))
[4 MEM[base: _111, offset: 0B]+0 S4 A16])
    GENERAL_REGS, RELOAD_FOR_INPUT (opnum = 1), optional
    reload_in_reg: (mem/f:SI (post_inc:SI (reg:SI 829 [ ivtmp.1067 ])) [4
MEM[base: _111, offset: 0B]+0 S4 A16])


So I am not sure if there are some bugs in reload for m68k, or ivopt is doing
something very trick and wrong?

Thanks,
bin