On Mon, Feb 26, 2024 at 03:15:02PM +0100, Richard Biener wrote:
> When folding a multiply CHRECs are handled like {a, +, b} * c
> is {a*c, +, b*c} but that isn't generally correct when overflow
> invokes undefined behavior. The following uses unsigned arithmetic
> unless either a is zero or a and b have the same sign.
>
> I've used simple early outs for INTEGER_CSTs and otherwise use
> a range-query since we lack a tree_expr_nonpositive_p.
>
> Bootstrapped and tested on x86_64-unknown-linux-gnu.
>
> I'm not sure it's worth using ranger, there might be also more
> cases where the integer multiply is OK, say when abs (A) > abs (B).
> But also {-2, +, 2}, but not for {1, +, -1} for example.
So, given that we found that get_range_pos_neg is not what you want,
I think the patch is ok, except a minor nit
> @@ -428,10 +434,41 @@ chrec_fold_multiply (tree type,
> if (integer_zerop (op1))
> return build_int_cst (type, 0);
>
> - return build_polynomial_chrec
> - (CHREC_VARIABLE (op0),
> - chrec_fold_multiply (type, CHREC_LEFT (op0), op1),
> - chrec_fold_multiply (type, CHREC_RIGHT (op0), op1));
> + /* When overflow is undefined and CHREC_LEFT/RIGHT do not have the
> + same sign or CHREC_LEFT is zero then folding the multiply into
> + the addition does not have the same behavior on overflow. Use
> + unsigned arithmetic in that case. */
> + value_range rl, rr;
> + if (!ANY_INTEGRAL_TYPE_P (type)
> + || TYPE_OVERFLOW_WRAPS (type)
> + || integer_zerop (CHREC_LEFT (op0))
> + || (TREE_CODE (CHREC_LEFT (op0)) == INTEGER_CST
> + && TREE_CODE (CHREC_RIGHT (op0)) == INTEGER_CST
> + && (tree_int_cst_sgn (CHREC_LEFT (op0))
> + == tree_int_cst_sgn (CHREC_RIGHT (op0))))
> + || (get_range_query (cfun)->range_of_expr (rl, CHREC_LEFT (op0))
> + && !rl.undefined_p ()
> + && (rl.nonpositive_p () || rl.nonnegative_p ())
> + && get_range_query (cfun)->range_of_expr (rr, CHREC_RIGHT
> (op0))
> + && !rr.undefined_p ()
> + && ((rl.nonpositive_p () && rr.nonpositive_p ())
> + || (rl.nonnegative_p () && rr.nonnegative_p ()))))
> + return build_polynomial_chrec
> + (CHREC_VARIABLE (op0),
> + chrec_fold_multiply (type, CHREC_LEFT (op0), op1),
> + chrec_fold_multiply (type, CHREC_RIGHT (op0), op1));
> + else
> + {
> + tree utype = unsigned_type_for (type);
> + op1 = chrec_convert_rhs (utype, op1);
> + tree tem = build_polynomial_chrec
> + (CHREC_VARIABLE (op0),
> + chrec_fold_multiply
> + (utype, chrec_convert_rhs (utype, CHREC_LEFT (op0)), op1),
> + chrec_fold_multiply
> + (utype, chrec_convert_rhs (utype, CHREC_RIGHT (op0)), op1));
> + return chrec_convert_rhs (type, tem);
When you touch these, can you please rewrite it to more readable code with
temporaries, instead of the ugly calls with ( on different line from the
function name?
{
tree left = chrec_fold_multiply (type, CHREC_LEFT (op0), op1);
tree right = chrec_fold_multiply (type, CHREC_RIGHT (op0), op1);
return build_polynomial_chrec (CHREC_VARIABLE (op0),
left, right);
}
and
tree left = chrec_convert_rhs (utype, CHREC_LEFT (op0));
left = chrec_fold_multiply (utype, left, op1);
tree right = chrec_convert_rhs (utype, CHREC_RIGHT (op0));
right = chrec_fold_multiply (utype, right, op1);
tree tem = build_polynomial_chrec (CHREC_VARIABLE (op0),
left, right);
return chrec_convert_rhs (type, tem);
?
Jakub
