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10.3.4 Comparing ordered poly_ints ¶

In cases where there is a definite link between two poly_ints, such as the outer and inner sizes of subregs, we usually require the sizes to be ordered by the known_le partial order. poly_int provides the following utility functions for ordered values:

‘ordered_p (a, b)’

Return true if a and b are ordered by the known_le partial order.

‘ordered_min (a, b)’

Assert that a and b are ordered by known_le and return the minimum of the two. When using this function, please add a comment explaining why the values are known to be ordered.

‘ordered_max (a, b)’

Assert that a and b are ordered by known_le and return the maximum of the two. When using this function, please add a comment explaining why the values are known to be ordered.

For example, if a subreg has an outer mode of size outer and an inner mode of size inner:

• the subreg is complete if known_eq (inner, outer)
• otherwise, the subreg is paradoxical if known_le (inner, outer)
• otherwise, the subreg is partial if known_le (outer, inner)
• otherwise, the subreg is ill-formed

Thus the subreg is only valid if ‘ordered_p (outer, inner)’ is true. If this condition is already known to be true then:

• the subreg is complete if known_eq (inner, outer)
• the subreg is paradoxical if maybe_lt (inner, outer)
• the subreg is partial if maybe_lt (outer, inner)

with the three conditions being mutually exclusive.

Code that checks whether a subreg is valid would therefore generally check whether ordered_p holds (in addition to whatever other checks are required for subreg validity). Code that is dealing with existing subregs can assert that ordered_p holds and use either of the classifications above.