https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69726
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |diagnostic,
| |missed-optimization
Status|UNCONFIRMED |NEW
Last reconfirmed| |2016-02-09
CC| |rguenth at gcc dot gnu.org
Summary|Bogus warnings with -O3 |Bogus warnings with -O3
|-Wuninitialized |-Wuninitialized because of
| |if-conversion
Ever confirmed|0 |1
--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
So at uninit time we have
<bb 2>:
vect__117.6_137 = MEM[(const int32_t *)block_8(D) + 32B];
vect__118.9_138 = MEM[(const int32_t *)block_8(D) + 64B];
vect__119.10_139 = vect__117.6_137 | vect__118.9_138;
vect__120.13_140 = MEM[(const int32_t *)block_8(D) + 96B];
vect__121.14_141 = vect__119.10_139 | vect__120.13_140;
vect__122.17_142 = MEM[(const int32_t *)block_8(D) + 128B];
vect__123.18_143 = vect__121.14_141 | vect__122.17_142;
vect__124.21_144 = MEM[(const int32_t *)block_8(D) + 160B];
vect__125.22_145 = vect__123.18_143 | vect__124.21_144;
vect__126.25_146 = MEM[(const int32_t *)block_8(D) + 192B];
vect__127.26_147 = vect__125.22_145 | vect__126.25_146;
vect__128.29_148 = MEM[(const int32_t *)block_8(D) + 224B];
vect__129.30_149 = vect__127.26_147 | vect__128.29_148;
vect__130.33_150 = MEM[(const int32_t *)block_8(D)];
vect__ifc__525.36_152 = MEM[(int *)&temp + 224B];
vect__ifc__523.38_154 = VEC_COND_EXPR <vect__129.30_149 == { 0, 0, 0, 0 },
vect__130.33_150, vect__ifc__525.36_152>;
vect__ifc__522.43_157 = MEM[(int *)&temp + 192B];
vect__ifc__520.45_159 = VEC_COND_EXPR <vect__129.30_149 == { 0, 0, 0, 0 },
vect__130.33_150, vect__ifc__522.43_157>;
vect__ifc__519.50_499 = MEM[(int *)&temp + 160B];
vect__ifc__517.52_161 = VEC_COND_EXPR <vect__129.30_149 == { 0, 0, 0, 0 },
vect__130.33_150, vect__ifc__519.50_499>;
vect__ifc__516.57_497 = MEM[(int *)&temp + 128B];
vect__ifc__514.59_163 = VEC_COND_EXPR <vect__129.30_149 == { 0, 0, 0, 0 },
vect__130.33_150, vect__ifc__516.57_497>;
vect__ifc__513.64_495 = MEM[(int *)&temp + 96B];
vect__ifc__511.66_493 = VEC_COND_EXPR <vect__129.30_149 == { 0, 0, 0, 0 },
vect__130.33_150, vect__ifc__513.64_495>;
vect__ifc__510.71_492 = MEM[(int *)&temp + 64B];
vect__ifc__508.73_486 = VEC_COND_EXPR <vect__129.30_149 == { 0, 0, 0, 0 },
vect__130.33_150, vect__ifc__510.71_492>;
vect__ifc__507.78_484 = MEM[(int *)&temp + 32B];
...
which means they are used conditional on vect__129.30_149 != { 0, 0, 0, 0 }.
But temp itself is never initialized.
This is caused by if-conversion which transforms
<bb 3>:
# i_199 = PHI <i_12(7), 0(2)>
# ivtmp_624 = PHI <ivtmp_623(7), 8(2)>
_6 = (long unsigned int) i_199;
_7 = _6 * 4;
_9 = block_8(D) + _7;
_10 = &temp + _7;
_117 = MEM[(const int32_t *)_9 + 32B];
_118 = MEM[(const int32_t *)_9 + 64B];
_119 = _117 | _118;
_120 = MEM[(const int32_t *)_9 + 96B];
_121 = _119 | _120;
_122 = MEM[(const int32_t *)_9 + 128B];
_123 = _121 | _122;
_124 = MEM[(const int32_t *)_9 + 160B];
_125 = _123 | _124;
_126 = MEM[(const int32_t *)_9 + 192B];
_127 = _125 | _126;
_128 = MEM[(const int32_t *)_9 + 224B];
_129 = _127 | _128;
if (_129 == 0)
goto <bb 4>;
else
goto <bb 5>;
<bb 4>:
_130 = MEM[(const int32_t *)_9];
MEM[(int *)_10 + 224B] = _130;
MEM[(int *)_10 + 192B] = _130;
MEM[(int *)_10 + 160B] = _130;
MEM[(int *)_10 + 128B] = _130;
MEM[(int *)_10 + 96B] = _130;
MEM[(int *)_10 + 64B] = _130;
MEM[(int *)_10 + 32B] = _130;
MEM[(int *)&temp][i_199] = _130;
goto <bb 6>;
<bb 5>:
_131 = MEM[(const int32_t *)_9];
a0_132 = _122 + _131;
a1_133 = _131 - _122;
a2_134 = _118 + _126;
_135 = _118 - _126;
_136 = _135 * 2896;
a3_137 = _136 >> 11;
a4_138 = _120 + _124;
a5_139 = _124 - _120;
a6_140 = _117 + _128;
a7_141 = _117 - _128;
b0_142 = a4_138 + a6_140;
_143 = a5_139 + a7_141;
_144 = _143 * 3784;
b1_145 = _144 >> 11;
_146 = a5_139 * -5352;
_147 = _146 >> 11;
_148 = _147 - b0_142;
b2_149 = b1_145 + _148;
_150 = a6_140 - a4_138;
_151 = _150 * 2896;
_152 = _151 >> 11;
b3_153 = _152 - b2_149;
_154 = a7_141 * 2217;
_155 = _154 >> 11;
_156 = b3_153 + _155;
b4_157 = _156 - b1_145;
_158 = a0_132 + a2_134;
_159 = b0_142 + _158;
MEM[(int *)&temp][i_199] = _159;
_160 = a1_133 + a3_137;
_161 = _160 - a2_134;
_162 = b2_149 + _161;
MEM[(int *)_10 + 32B] = _162;
_163 = a1_133 - a3_137;
_164 = a2_134 + _163;
_165 = b3_153 + _164;
MEM[(int *)_10 + 64B] = _165;
_166 = a0_132 - a2_134;
_167 = _166 - b4_157;
MEM[(int *)_10 + 96B] = _167;
_168 = b4_157 + _166;
MEM[(int *)_10 + 128B] = _168;
_169 = _164 - b3_153;
MEM[(int *)_10 + 160B] = _169;
_170 = _161 - b2_149;
MEM[(int *)_10 + 192B] = _170;
_171 = _158 - b0_142;
MEM[(int *)_10 + 224B] = _171;
<bb 6>:
i_12 = i_199 + 1;
ivtmp_623 = ivtmp_624 - 1;
if (ivtmp_623 != 0)
goto <bb 7>;
else
goto <bb 8>;
<bb 7>:
goto <bb 3>;
into
<bb 4>:
# i_199 = PHI <i_12(5), 0(3)>
# ivtmp_624 = PHI <ivtmp_623(5), 8(3)>
_6 = (long unsigned int) i_199;
_7 = _6 * 4;
_9 = block_8(D) + _7;
_10 = &temp + _7;
_117 = MEM[(const int32_t *)_9 + 32B];
_118 = MEM[(const int32_t *)_9 + 64B];
_119 = _117 | _118;
_120 = MEM[(const int32_t *)_9 + 96B];
_121 = _119 | _120;
_122 = MEM[(const int32_t *)_9 + 128B];
_123 = _121 | _122;
_124 = MEM[(const int32_t *)_9 + 160B];
_125 = _123 | _124;
_126 = MEM[(const int32_t *)_9 + 192B];
_127 = _125 | _126;
_128 = MEM[(const int32_t *)_9 + 224B];
_129 = _127 | _128;
_130 = MEM[(const int32_t *)_9];
_ifc__525 = MEM[(int *)_10 + 224B];
_ifc__524 = _130;
_ifc__523 = _129 == 0 ? _ifc__524 : _ifc__525;
MEM[(int *)_10 + 224B] = _ifc__523;
_ifc__522 = MEM[(int *)_10 + 192B];
_ifc__521 = _130;
_ifc__520 = _129 == 0 ? _ifc__521 : _ifc__522;
MEM[(int *)_10 + 192B] = _ifc__520;
_ifc__519 = MEM[(int *)_10 + 160B];
_ifc__518 = _130;
_ifc__517 = _129 == 0 ? _ifc__518 : _ifc__519;
MEM[(int *)_10 + 160B] = _ifc__517;
_ifc__516 = MEM[(int *)_10 + 128B];
_ifc__515 = _130;
_ifc__514 = _129 == 0 ? _ifc__515 : _ifc__516;
MEM[(int *)_10 + 128B] = _ifc__514;
_ifc__513 = MEM[(int *)_10 + 96B];
_ifc__512 = _130;
_ifc__511 = _129 == 0 ? _ifc__512 : _ifc__513;
MEM[(int *)_10 + 96B] = _ifc__511;
_ifc__510 = MEM[(int *)_10 + 64B];
_ifc__509 = _130;
_ifc__508 = _129 == 0 ? _ifc__509 : _ifc__510;
MEM[(int *)_10 + 64B] = _ifc__508;
_ifc__507 = MEM[(int *)_10 + 32B];
_ifc__506 = _130;
_ifc__505 = _129 == 0 ? _ifc__506 : _ifc__507;
MEM[(int *)_10 + 32B] = _ifc__505;
_ifc__504 = MEM[(int *)&temp][i_199];
_ifc__503 = _130;
_ifc__502 = _129 == 0 ? _ifc__503 : _ifc__504;
MEM[(int *)&temp][i_199] = _ifc__502;
_131 = MEM[(const int32_t *)_9];
a0_132 = _122 + _131;
a1_133 = _131 - _122;
a2_134 = _118 + _126;
_135 = _118 - _126;
_136 = _135 * 2896;
a3_137 = _136 >> 11;
a4_138 = _120 + _124;
a5_139 = _124 - _120;
a6_140 = _117 + _128;
a7_141 = _117 - _128;
b0_142 = a4_138 + a6_140;
_143 = a5_139 + a7_141;
_144 = _143 * 3784;
b1_145 = _144 >> 11;
_146 = a5_139 * -5352;
_147 = _146 >> 11;
_148 = _147 - b0_142;
b2_149 = b1_145 + _148;
_150 = a6_140 - a4_138;
_151 = _150 * 2896;
_152 = _151 >> 11;
b3_153 = _152 - b2_149;
_154 = a7_141 * 2217;
_155 = _154 >> 11;
_156 = b3_153 + _155;
b4_157 = _156 - b1_145;
_158 = a0_132 + a2_134;
_159 = b0_142 + _158;
_ifc__501 = MEM[(int *)&temp][i_199];
_ifc__500 = _159;
_ifc__499 = _129 == 0 ? _ifc__501 : _ifc__500;
MEM[(int *)&temp][i_199] = _ifc__499;
_160 = a1_133 + a3_137;
_161 = _160 - a2_134;
_162 = b2_149 + _161;
_ifc__498 = MEM[(int *)_10 + 32B];
_ifc__497 = _162;
_ifc__496 = _129 == 0 ? _ifc__498 : _ifc__497;
MEM[(int *)_10 + 32B] = _ifc__496;
_163 = a1_133 - a3_137;
_164 = a2_134 + _163;
_165 = b3_153 + _164;
_ifc__495 = MEM[(int *)_10 + 64B];
_ifc__494 = _165;
_ifc__493 = _129 == 0 ? _ifc__495 : _ifc__494;
MEM[(int *)_10 + 64B] = _ifc__493;
_166 = a0_132 - a2_134;
_167 = _166 - b4_157;
_ifc__492 = MEM[(int *)_10 + 96B];
_ifc__487 = _167;
_ifc__486 = _129 == 0 ? _ifc__492 : _ifc__487;
MEM[(int *)_10 + 96B] = _ifc__486;
_168 = b4_157 + _166;
_ifc__485 = MEM[(int *)_10 + 128B];
_ifc__484 = _168;
_ifc__483 = _129 == 0 ? _ifc__485 : _ifc__484;
MEM[(int *)_10 + 128B] = _ifc__483;
_169 = _164 - b3_153;
_ifc__482 = MEM[(int *)_10 + 160B];
_ifc__481 = _169;
_ifc__480 = _129 == 0 ? _ifc__482 : _ifc__481;
MEM[(int *)_10 + 160B] = _ifc__480;
_170 = _161 - b2_149;
_ifc__479 = MEM[(int *)_10 + 192B];
_ifc__478 = _170;
_ifc__477 = _129 == 0 ? _ifc__479 : _ifc__478;
MEM[(int *)_10 + 192B] = _ifc__477;
_171 = _158 - b0_142;
_ifc__476 = MEM[(int *)_10 + 224B];
_ifc__475 = _171;
_ifc__474 = _129 == 0 ? _ifc__476 : _ifc__475;
MEM[(int *)_10 + 224B] = _ifc__474;
i_12 = i_199 + 1;
ivtmp_623 = ivtmp_624 - 1;
if (ivtmp_623 != 0)
goto <bb 5>;
else
goto <bb 12>;
<bb 5>:
goto <bb 4>;
note how this transforms
if (pred)
temp[i] = ...;
else
temp[i] = ...;
into
tem = temp[i];
temp[i] = pred ? ... : tem;
tem2 = temp[i];
temp[i] = !pred ? ... : tem;
and thus reads from uninitialized temp[]. Part of the GIMPLE IL is
_ifc__525 = MEM[(int *)_10 + 224B];
_ifc__524 = _130;
_ifc__523 = _129 == 0 ? _ifc__524 : _ifc__525;
MEM[(int *)_10 + 224B] = _ifc__523;
...
_ifc__476 = MEM[(int *)_10 + 224B];
_ifc__475 = _171;
_ifc__474 = _129 == 0 ? _ifc__476 : _ifc__475;
MEM[(int *)_10 + 224B] = _ifc__474;
Confirmed also as missed optimization, if-conversion should do a better
job for this. OTOH we miss a general scalar transform that would sink
stores to common locations to the merger block, then if-conversion would
have a simpler job.
