On Mon, Jan 2, 2012 at 3:09 PM, Amker.Cheng <amker.ch...@gmail.com> wrote:
> On Mon, Jan 2, 2012 at 9:37 PM, Richard Guenther
> <richard.guent...@gmail.com> wrote:
>
>> Well, with
>>
>> Index: gcc/tree-ssa-pre.c
>> ===================================================================
>> --- gcc/tree-ssa-pre.c (revision 182784)
>> +++ gcc/tree-ssa-pre.c (working copy)
>> @@ -4335,16 +4335,23 @@ eliminate (void)
>> available value-numbers. */
>> else if (gimple_code (stmt) == GIMPLE_COND)
>> {
>> - tree op0 = gimple_cond_lhs (stmt);
>> - tree op1 = gimple_cond_rhs (stmt);
>> + tree op[2];
>> tree result;
>> + vn_nary_op_t nary;
>>
>> - if (TREE_CODE (op0) == SSA_NAME)
>> - op0 = VN_INFO (op0)->valnum;
>> - if (TREE_CODE (op1) == SSA_NAME)
>> - op1 = VN_INFO (op1)->valnum;
>> + op[0] = gimple_cond_lhs (stmt);
>> + op[1] = gimple_cond_rhs (stmt);
>> + if (TREE_CODE (op[0]) == SSA_NAME)
>> + op[0] = VN_INFO (op[0])->valnum;
>> + if (TREE_CODE (op[1]) == SSA_NAME)
>> + op[1] = VN_INFO (op[1])->valnum;
>> result = fold_binary (gimple_cond_code (stmt),
>> boolean_type_node,
>> - op0, op1);
>> + op[0], op[1]);
>> + if (!result)
>> + result = vn_nary_op_lookup_pieces (2, gimple_cond_code
>> (stmt),
>> + boolean_type_node,
>> + op, &nary);
>> +
>> if (result && TREE_CODE (result) == INTEGER_CST)
>> {
>> if (integer_zerop (result))
>> @@ -4354,6 +4361,13 @@ eliminate (void)
>> update_stmt (stmt);
>> todo = TODO_cleanup_cfg;
>> }
>> + else if (result && TREE_CODE (result) == SSA_NAME)
>> + {
>> + gimple_cond_set_code (stmt, NE_EXPR);
>> + gimple_cond_set_lhs (stmt, result);
>> + gimple_cond_set_rhs (stmt, boolean_false_node);
>> + update_stmt (stmt);
>> + }
>> }
>> /* Visit indirect calls and turn them into direct calls if
>> possible. */
>>
>> you get the CSE (too simple patch, you need to check leaders properly).
>> You can then add similar lookups for an inverted conditional.
>
> Thanks for your explanation. On shortcoming of this method is that it
> cannot find/take cond_expr(and the implicitly defined variable) as the
> leader in pre. I guess this is why you said it can handle a subset of all
> cases in previous message?
Yes. It won't handle
if (x > 1)
...
tem = x > 1;
or
if (x > 1)
...
if (x > 1)
though maybe we could teach PRE to do the insertion by properly
putting x > 1 into EXP_GEN in compute_avail (but not into AVAIL_OUT).
Not sure about this though. Currently we don't do anything to
GIMPLE_COND operands (which seems odd anyway, we should
at least add the operands to EXP_GEN).
> on the other hand, I like this method, given the simplicity especially. :)
Yeah.
> --
> Best Regards.
