Return type op fast path results without the full fulfillment machinery [-0.83% avg] - #30
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Query type ops check their fast paths (trivial sizedness proofs, alias free normalizations) inside the closure passed to scrape_region_constraints, so every fast path hit still paid for an inference snapshot, an ObligationCtxt with a boxed fulfillment engine, and the region constraint scraping itself, all over empty data. MIR type check issues several type ops per statement and the overwhelming majority hit a fast path.
Fast path results are final: they register no obligations and produce no region constraints, so the fast path is now checked once at the top of fully_perform and the result returned directly. resolve_vars_if_possible is kept on the returned value, matching what scrape_region_constraints did before.
Skipping the scrape requires that no region state is pending on the inference context between type ops. The one place that violated this, the eager hidden type equation reached from relate_opaques, now rolls back on failure via commit_if_ok, and the fast path asserts the invariant through a new InferCtxt::has_pending_region_state helper.