Looks good to me.
2012/4/5 Wu Yongchong <wuyongch...@gmail.com>
> Hi, all
>
> Can someone help review this patch.
>
> 1. Bug descript
> The hash function for VN_BINARY_EXPR will first canonicalize the
> expression. as the following code in file opt_vn_expr_taxonomy.h:509
> size_t hash()
> {
> Is_True(!has_bottom_opnd() && !has_top_opnd(),
> ("Cannot hash() with Top() or Bottom() operand!"));
> _canonicalize();
> return _opc + (_vn[0].ordinal() << 4) + (_vn[1].ordinal() << 8);
> }
>
> Following is the canonicalize code in opt_vn_expr.cxx:754
>
> void
> VN_BINARY_EXPR::_canonicalize()
> {
> // Puts operands in increasing order of VN if commutative,
> // and change opcode for inequalities such that we always
> // use LT or LE and never GT or GE.
> //
> OPCODE opc1 = OPCODE_commutative_op(_opc);
> if (opc1 != OPCODE_UNKNOWN && _vn[0] > _vn[1])
> {
> Switch_Vn_Opnd(_vn[0], _vn[1]);
> _opc = opc1;
> }
> else
> {
> const OPERATOR opr = OPCODE_operator(_opc);
> if (opr == OPR_GE)
> {
> Switch_Vn_Opnd(_vn[0], _vn[1]);
> _opc = OPCODE_make_op(OPR_LE, OPCODE_rtype(_opc),
> OPCODE_desc(_opc));
> }
> else if (opr == OPR_GT)
> {
> Switch_Vn_Opnd(_vn[0], _vn[1]);
> _opc = OPCODE_make_op(OPR_LT, OPCODE_rtype(_opc),
> OPCODE_desc(_opc));
> }
> }
> } // VN_BINARY_EXPR::_canonicalize
>
> These code would like to do one of the 2 things as in the comments
> a. put operands in increasing order of VN if commutative
> b. use LT or LE and never GT or GE
> For the expression v0 < v1 where Value_number(v0) = 3 ,
> Value_number(v2)= 1 . we try to get it’s hash number. as it satisfy
> opc1 != OPCODE_UNKNOWN && _vn [0] > _vn[1], it will canonicalize to
> v1 > v0
> The second time we try to get it’s hash number, in this time , this
> expression satisfy rule a, it will jump to rule b, use LT or LE . So
> v1 > v0 will canonicalize to v0 < v1 again. We got a different hash
> number from the first time.
> The hash number is not unique for this expression.
> Actually, the relative operators are not consider to be commutatived.
> Only binary operations that the operands can be exchange and the
> operator keep the same are commutatived operations, just like plus,
> multiple, etc.
>
> Do not apply rule a for relative operator(LT, LE, GT, GE) should be a
> solution.
>
> Index: osprey/be/opt/opt_vn_expr.cxx
> ===================================================================
> --- osprey/be/opt/opt_vn_expr.cxx (revision 3901)
> +++ osprey/be/opt/opt_vn_expr.cxx (working copy)
> @@ -759,24 +759,15 @@
> // use LT or LE and never GT or GE.
> //
> OPCODE opc1 = OPCODE_commutative_op(_opc);
> - if (opc1 != OPCODE_UNKNOWN && _vn[0] > _vn[1])
> + const OPERATOR opr = OPCODE_operator(_opc);
> + if (opc1 == _opc && _vn[0] > _vn[1])
> {
> Switch_Vn_Opnd(_vn[0], _vn[1]);
> - _opc = opc1;
> }
> - else
> + else if (opr == OPR_GE || opr == OPR_GT )
> {
> - const OPERATOR opr = OPCODE_operator(_opc);
> - if (opr == OPR_GE)
> - {
> - Switch_Vn_Opnd(_vn[0], _vn[1]);
> - _opc = OPCODE_make_op(OPR_LE, OPCODE_rtype(_opc),
> OPCODE_desc(_opc));
> - }
> - else if (opr == OPR_GT)
> - {
> - Switch_Vn_Opnd(_vn[0], _vn[1]);
> - _opc = OPCODE_make_op(OPR_LT, OPCODE_rtype(_opc),
> OPCODE_desc(_opc));
> - }
> + Switch_Vn_Opnd(_vn[0], _vn[1]);
> + _opc = opc1;
> }
> } // VN_BINARY_EXPR::_canonicalize
>
>
>
>
>
> --
> yongchong
>
>
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--
Regards,
Lai Jian-Xin
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