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[Bug tree-optimization/70509] New: wrong code with extract from a casted vector(64)


https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70509

            Bug ID: 70509
           Summary: wrong code with extract from a casted vector(64)
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Keywords: wrong-code
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: zsojka at seznam dot cz
  Target Milestone: ---
            Target: x86_64-pc-linux-gnu

Created attachment 38159
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=38159&action=edit
reduced testcase

Output:
$ gcc -O -mavx512bw testcase.c
$ sde64 -- ./a.out 
00000008
Aborted

First broken dump seems to be .forwprop, where is:
  _2 = VIEW_CONVERT_EXPR<vector(64) charD.7>(v_1(D));
  _4 = VEC_PERM_EXPR <_2, _2, { 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32,
32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32,
32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32,
32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32 }>;
  _9 = BIT_FIELD_REF <u_8(D), 8, 0>;
  _10 = BIT_FIELD_REF <_2, 8, 0>;
  _11 = _9 / _10;

It extracts from _2 offset 0 instead of 256. -fno-tree-forwprop fixes the
testcase.

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