Skip Ty w/o infer ty/const in trait select

[JulianKnodt]

Remove some allocations & also add skip_current_subtree to skip subtrees with no inferred items.

r? @eddyb since marked in the FIXME

[jonas-schievink]

@bors try @rust-timer queue

[rust-timer]

Awaiting bors try build completion.

[bors]

⌛ Trying commit 690027c63747292a6e9892d6e695ab78f3dcbb1b with merge 84fa9d2d81ecada2009acc0e4984e4301bf5f721...

[bors]

☀️ Try build successful - checks-actions
Build commit: 84fa9d2d81ecada2009acc0e4984e4301bf5f721 (84fa9d2d81ecada2009acc0e4984e4301bf5f721)

[rust-timer]

Queued 84fa9d2d81ecada2009acc0e4984e4301bf5f721 with parent 2987785, future comparison URL.

@rustbot label: +S-waiting-on-perf

[rust-timer]

Finished benchmarking try commit (84fa9d2d81ecada2009acc0e4984e4301bf5f721): comparison url.

Benchmarking this pull request likely means that it is perf-sensitive, so we're automatically marking it as not fit for rolling up. Please note that if the perf results are neutral, you should likely undo the rollup=never given below by specifying rollup- to bors.

Importantly, though, if the results of this run are non-neutral do not roll this PR up -- it will mask other regressions or improvements in the roll up.

@bors rollup=never
@rustbot label: +S-waiting-on-review -S-waiting-on-perf

[JohnCSimon]

ping from triage:
@JulianKnodt - can you please address the merge conflict?

@rustbot label: -S-waiting-on-review +S-waiting-on-author

[JulianKnodt]

@rustbot label: +S-waiting-on-review -S-waiting-on-author

@eddyb if you're too busy to review this can you assign it to someone else?

[eddyb]

I am not in the review rotation anymore, sorry!

r? @matthewjasper or @nikomatsakis

[matthewjasper]

@bors r+

[bors]

📌 Commit 899f27d has been approved by matthewjasper

[bors]

⌛ Testing commit 899f27d with merge 94736c4...

[bors]

☀️ Test successful - checks-actions
Approved by: matthewjasper
Pushing 94736c4 to master...