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Date: Wed, 11 Aug 2021 08:15:37 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D101858

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |12.0
          Component|c                           |middle-end
             Status|NEW                         |ASSIGNED

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
#0  build2 (code=3DRSHIFT_EXPR, tt=3D<pointer_type 0x7ffff65649d8>,=20
    arg0=3D<convert_expr 0x7ffff6686260>, arg1=3D<parm_decl 0x7ffff669d000 =
a>)
    at /home/rguenther/src/gcc2/gcc/tree.c:4970
#1  0x0000000000eb1bab in fold_binary_loc (loc=3D2147483651, code=3DLT_EXPR=
,=20
    type=3D<integer_type 0x7ffff655c5e8 int>, op0=3D<convert_expr 0x7ffff66=
86260>,=20
    op1=3D<convert_expr 0x7ffff6686220>)
    at /home/rguenther/src/gcc2/gcc/fold-const.c:12510

      /* Similarly for X < (cast) (1 << Y).  But cast can't be narrowing,
         otherwise Y might be >=3D # of bits in X's type and thus e.g.
         (unsigned char) (1 << Y) for Y 15 might be 0.
         If the cast is widening, then 1 << Y should have unsigned type,
         otherwise if Y is number of bits in the signed shift type minus 1,
         we can't optimize this.  E.g. (unsigned long long) (1 << Y) for Y
         31 might be 0xffffffff80000000.  */
      if ((code =3D=3D LT_EXPR || code =3D=3D GE_EXPR)
          && TYPE_UNSIGNED (TREE_TYPE (arg0))
          && CONVERT_EXPR_P (arg1)
          && TREE_CODE (TREE_OPERAND (arg1, 0)) =3D=3D LSHIFT_EXPR
          && (element_precision (TREE_TYPE (arg1))
              >=3D element_precision (TREE_TYPE (TREE_OPERAND (arg1, 0))))
          && (TYPE_UNSIGNED (TREE_TYPE (TREE_OPERAND (arg1, 0)))
              || (element_precision (TREE_TYPE (arg1))
                  =3D=3D element_precision (TREE_TYPE (TREE_OPERAND (arg1, =
0)))))
          && integer_onep (TREE_OPERAND (TREE_OPERAND (arg1, 0), 0)))
        {
          tem =3D build2 (RSHIFT_EXPR, TREE_TYPE (arg0), arg0,
                        TREE_OPERAND (TREE_OPERAND (arg1, 0), 1));
          return build2_loc (loc, code =3D=3D LT_EXPR ? EQ_EXPR : NE_EXPR, =
type,
                             fold_convert_loc (loc, TREE_TYPE (arg0), tem),
                             build_zero_cst (TREE_TYPE (arg0)));
        }

Mine.=