Reinstate fast_reject for overlap checking
The initial implementation of specialization did not use the
`fast_reject` mechanism when checking for overlap, which caused a
serious performance regression in some cases.
This commit modifies the specialization graph to use simplified types
for fast rejection when possible, and along the way refactors the logic
for building the specialization graph.
Closes#32499
r? @nikomatsakis
The initial implementation of specialization did not use the
`fast_reject` mechanism when checking for overlap, which caused a
serious performance regression in some cases.
This commit modifies the specialization graph to use simplified types
for fast rejection when possible, and along the way refactors the logic
for building the specialization graph.
Closes#32499