On 11/27/2014 09:26 AM, Marek Polacek wrote:
On Wed, Nov 26, 2014 at 11:56:26AM -0500, Jason Merrill wrote:
Please give diagnostics explaining what's wrong with the shift rather than
the generic "is not a constant expression".
Done.
I was thinking even more detailed: one diagnostic for negative count,
one diagnostic for count larger than the precision of the lhs, and then
a third for overflow.
+ tree t = build_int_cst (unsigned_type_node, uprec - 1);
+ t = fold_build2 (MINUS_EXPR, unsigned_type_node, t, rhs);
+ tree ulhs = fold_convert (unsigned_type_for (lhstype), lhs);
+ t = fold_build2 (RSHIFT_EXPR, TREE_TYPE (ulhs), ulhs, t);
+ if (tree_int_cst_lt (integer_one_node, t))
This could also use a comment explaining the logic.
+ /* For signed x << y the following:
+ (unsigned) x >> ((prec (lhs) - 1) - y)
+ if > 1, is undefined. */
I meant briefly explaining where that formula comes from.
Jason
