On Thu, 5 Jul 2007, Roman Zippel wrote:
> Hi,
>
> On Thu, 5 Jul 2007, Richard Guenther wrote:
>
> > If there is anything to fix, then all those variants should produce
> > the same code, not just foo3 and foo4. So for these cases we should
> > make sure that value-numbering sees them as computing the same value
> > and extend combine to choose the instructions with the least cost.
> >
> > Changing fold isn't a real fix. It's a workaround for a specific
> > testcase.
>
> What do you suggest now specifically?
> combine isn't the problem here, at the time we reach RTL this should
> already be done. Your patch only catches specific cases and pessimises
> others.
Well, that's always the nature of any canonicalization.
The following actually makes SCCVN notice that tmp1 == tmp2 in
int foo3(int x, int y)
{
int tmp1 = (x * y) + (y * 5);
int tmp2;
x *= y;
tmp2 = x + (y * 5);
return tmp1 == tmp2;
}
of course only tested on this particular testcase. It just shows
that it is possible to fix this in a generic way.
Richard.
Index: tree-ssa-sccvn.c
===================================================================
--- tree-ssa-sccvn.c (revision 126369)
+++ tree-ssa-sccvn.c (working copy)
@@ -1387,6 +1389,8 @@ simplify_binary_expression (tree rhs)
op0 = valueize_expr (VN_INFO (op0)->expr);
else if (SSA_VAL (op0) != VN_TOP && SSA_VAL (op0) != op0)
op0 = VN_INFO (op0)->valnum;
+ else
+ op0 = valueize_expr (VN_INFO (op0)->expr);
}
if (TREE_CODE (op1) == SSA_NAME)
@@ -1395,7 +1399,14 @@ simplify_binary_expression (tree rhs)
op1 = valueize_expr (VN_INFO (op1)->expr);
else if (SSA_VAL (op1) != VN_TOP && SSA_VAL (op1) != op1)
op1 = VN_INFO (op1)->valnum;
+ else
+ op1 = valueize_expr (VN_INFO (op1)->expr);
}
+
+ if (op0 == TREE_OPERAND (rhs, 0)
+ && op1 == TREE_OPERAND (rhs, 1))
+ return rhs;
+
result = fold_binary (TREE_CODE (rhs), TREE_TYPE (rhs), op0, op1);
/* Make sure result is not a complex expression consiting
@@ -1423,6 +1434,16 @@ simplify_binary_expression (tree rhs)
{
tree op0 = TREE_OPERAND (result, 0);
tree op1 = TREE_OPERAND (result, 1);
+ tree tmp0, tmp1;
+ if (EXPR_P (op0)
+ && (tmp0 = vn_binary_op_lookup (op0)))
+ {
+ tmp1 = vn_binary_op_lookup (build2 (TREE_CODE (result),
TREE_TYPE (result), tmp0, op1));
+ if (tmp1)
+ return tmp1;
+ }
+ if ((tmp0 = vn_binary_op_lookup (result)))
+ return tmp0;
if (!EXPR_P (op0) && !EXPR_P (op1))
return result;
}
@@ -1607,7 +1637,7 @@ visit_use (tree use)
even if they were optimistically constant. */
VN_INFO (lhs)->has_constants = false;
- VN_INFO (lhs)->expr = lhs;
+ VN_INFO (lhs)->expr = rhs;
}
if (TREE_CODE (lhs) == SSA_NAME
