On Mon, Jan 2, 2012 at 2:11 PM, Amker.Cheng <amker.ch...@gmail.com> wrote:
> Thanks Richard,
>
> On Mon, Jan 2, 2012 at 8:33 PM, Richard Guenther
> <richard.guent...@gmail.com> wrote:
>>
>> I've previously worked on changing GIMPLE_COND to no longer embed
>> the comparison but carry a predicate SSA_NAME only (this is effectively
>> what you do as pre-processing before SCCVN). It had some non-trivial
>> fallout (for example PRE get's quite confused and ends up separating
>> conditionals and jumps too far ...) so I didn't finish it.
> Here changing GIMPLE_COND to no longer embed the comparison,
> do you mean this only in fre/pre passes or in common?
> If only in fre/pre passes, when and how these changed GIMPLE_COND
> be changed back to normal ones?
> If in common, won't this affects passes working on GIMPLE_COND, like
> tree-ssa-forwprop.c?
Everywhere. I posted a patch early last year and changed COND_EXPRs
on the RHS of an assignment later.
>>
>> A subset of all cases can be catched by simply looking up the
>> N-ary at eliminate () time and re-writing the GIMPLE_COND to use
>> the predicate - which might not actually be beneficial (but forwprop
>> will undo not beneficial cases - hopefully).
>>
>> In the end I'd rather go the way changing the GIMPLE IL to not
>> embed the comparison in the GIMPLE_COND - that reduces
>> the amount of redundant way we can express the same thing.
> Will you try to handle the reversion comparison case as mentioned
> in my previous message? I guess this needs both sccvn and fre/pre's
> work. It would be great to hear your thoughts on this.
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.
Richard.
> Thanks
>
> --
> Best Regards.
