This is the mail archive of the gcc-bugs@gcc.gnu.org mailing list for the GCC project.


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]
Other format: [Raw text]

[Bug tree-optimization/59354] [4.8/4.9/5/Regression] Element swizzling produces invalid result with -O3


https://gcc.gnu.org/bugzilla/show_bug.cgi?id=59354

UroÅ Bizjak <ubizjak at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|[4.8/4.9/5/Regression]      |[4.8/4.9/5/Regression]
                   |Element swizzling produces  |Element swizzling produces
                   |invalid result with -O3     |invalid result with -O3
                   |(tree-cunrolli pass         |
                   |problem?)                   |

--- Comment #6 from UroÅ Bizjak <ubizjak at gmail dot com> ---
This is tree vectorizer problem, involving VECT_PACK_TRUNC expressions.

Initializing the source array with:

  for (i = 0; i < 256; i++)
    a[i] = i;

we can see the difference in the destination array:

-O2 (correct):

0, 1, 2, 3, 16, 17, 18, 19, 32, 33, 34, 35, 48, 49, 50, 51, 64, 65, 66, 67, 80,
81, 82, 83, 96, 97, 98, 99, 112, 113, 114, 115, 128, 129, 130, 131, 144, 145,
146, 147, 160, 161, 162, 163, 176, 177, 178, 179, 192, 193, 194, 195, 208, 209,
210, 211, 224, 225, 226, 227, 240, 241, 242, 243, 4, 5, 6, 7, 20, 21, 22, 23,
36, 37, 38, 39, 52, 53, 54, 55, 68, 69, 70, 71, 84, 85, 86, 87, 100, 101, 102,
103, 116, 117, 118, 119, 132, 133, 134, 135, 148, 149, 150, 151, 164, 165, 166,
167, 180, 181, 182, 183, 196, 197, 198, 199, 212, 213, 214, 215, 228, 229, 230,
231, 244, 245, 246, 247, 8, 9, 10, 11, 24, 25, 26, 27, 40, 41, 42, 43, 56, 57,
58, 59, 72, 73, 74, 75, 88, 89, 90, 91, 104, 105, 106, 107, 120, 121, 122, 123,
136, 137, 138, 139, 152, 153, 154, 155, 168, 169, 170, 171, 184, 185, 186, 187,
200, 201, 202, 203, 216, 217, 218, 219, 232, 233, 234, 235, 248, 249, 250, 251,
12, 13, 14, 15, 28, 29, 30, 31, 44, 45, 46, 47, 60, 61, 62, 63, 76, 77, 78, 79,
92, 93, 94, 95, 108, 109, 110, 111, 124, 125, 126, 127, 140, 141, 142, 143,
156, 157, 158, 159, 172, 173, 174, 175, 188, 189, 190, 191, 204, 205, 206, 207,
220, 221, 222, 223, 236, 237, 238, 239, 252, 253, 254, 255

-O3 (incorrect):

0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21,
22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41,
42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61,
62, 63, 4, 5, 6, 7, 20, 21, 22, 23, 36, 37, 38, 39, 52, 53, 54, 55, 68, 69, 70,
71, 84, 85, 86, 87, 100, 101, 102, 103, 116, 117, 118, 119, 132, 133, 134, 135,
148, 149, 150, 151, 164, 165, 166, 167, 180, 181, 182, 183, 196, 197, 198, 199,
212, 213, 214, 215, 228, 229, 230, 231, 244, 245, 246, 247, 8, 9, 10, 11, 24,
25, 26, 27, 40, 41, 42, 43, 56, 57, 58, 59, 72, 73, 74, 75, 88, 89, 90, 91,
104, 105, 106, 107, 120, 121, 122, 123, 136, 137, 138, 139, 152, 153, 154, 155,
168, 169, 170, 171, 184, 185, 186, 187, 200, 201, 202, 203, 216, 217, 218, 219,
232, 233, 234, 235, 248, 249, 250, 251, 12, 13, 14, 15, 28, 29, 30, 31, 44, 45,
46, 47, 60, 61, 62, 63, 76, 77, 78, 79, 92, 93, 94, 95, 108, 109, 110, 111,
124, 125, 126, 127, 140, 141, 142, 143, 156, 157, 158, 159, 172, 173, 174, 175,
188, 189, 190, 191, 204, 205, 206, 207, 220, 221, 222, 223, 236, 237, 238, 239,
252, 253, 254, 255

b[4] is already wrong.

This is the beginning of the optimized dump:

  vect__24.6_185 = MEM[(unsigned int *)&a];
  vect__24.7_182 = MEM[(unsigned int *)&a + 16B];
  vect__24.8_176 = MEM[(unsigned int *)&a + 32B];
  vect__24.9_173 = MEM[(unsigned int *)&a + 48B];
  vect__24.10_160 = MEM[(unsigned int *)&a + 64B];
  vect__24.11_158 = MEM[(unsigned int *)&a + 80B];
  vect__24.12_155 = MEM[(unsigned int *)&a + 96B];
  vect__24.13_148 = MEM[(unsigned int *)&a + 112B];
  vect__24.14_145 = MEM[(unsigned int *)&a + 128B];
  vect__24.15_138 = MEM[(unsigned int *)&a + 144B];
  vect__24.16_136 = MEM[(unsigned int *)&a + 160B];
  vect__24.17_133 = MEM[(unsigned int *)&a + 176B];
  vect__24.18_126 = MEM[(unsigned int *)&a + 192B];
  vect__24.19_124 = MEM[(unsigned int *)&a + 208B];
  vect__24.20_111 = MEM[(unsigned int *)&a + 224B];
  vect__24.21_108 = MEM[(unsigned int *)&a + 240B];
  vect__25.23_107 = VEC_PACK_TRUNC_EXPR <vect__24.6_185, vect__24.7_182>;
  vect__25.23_101 = VEC_PACK_TRUNC_EXPR <vect__24.8_176, vect__24.9_173>;
  vect__25.23_100 = VEC_PACK_TRUNC_EXPR <vect__24.10_160, vect__24.11_158>;
  vect__25.23_99 = VEC_PACK_TRUNC_EXPR <vect__24.12_155, vect__24.13_148>;
  vect__25.23_87 = VEC_PACK_TRUNC_EXPR <vect__24.14_145, vect__24.15_138>;
  vect__25.23_86 = VEC_PACK_TRUNC_EXPR <vect__24.16_136, vect__24.17_133>;
  vect__25.23_85 = VEC_PACK_TRUNC_EXPR <vect__24.18_126, vect__24.19_124>;
  vect__25.23_81 = VEC_PACK_TRUNC_EXPR <vect__24.20_111, vect__24.21_108>;
  vect__25.22_80 = VEC_PACK_TRUNC_EXPR <vect__25.23_107, vect__25.23_101>;
  vect__25.22_79 = VEC_PACK_TRUNC_EXPR <vect__25.23_100, vect__25.23_99>;
  vect__25.22_78 = VEC_PACK_TRUNC_EXPR <vect__25.23_87, vect__25.23_86>;
  vect__25.22_77 = VEC_PACK_TRUNC_EXPR <vect__25.23_85, vect__25.23_81>;
  MEM[(unsigned char[256] *)&b] = vect__25.22_80;
  MEM[(unsigned char[256] *)&b + 16B] = vect__25.22_79;
  MEM[(unsigned char[256] *)&b + 32B] = vect__25.22_78;
  MEM[(unsigned char[256] *)&b + 48B] = vect__25.22_77;

As can be seen, the first 64 elements of the destination array are simply
truncated first 64 elements of source array.

Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]