misc cleanups from debugging something

[BoxyUwU]

rename instantiate_canonical_with_fresh_inference_vars to instantiate_canonical the substs for the canonical are not solely infer vars as that would be wildly wrong and it is rather confusing to see this method called and think that the entire canonicalization setup is completely broken when it is not 👍

also update region debug printing to be more like the custom impls for Ty/Const, right now regions in debug output are horribly verbose and make it incredibly hard to read but with this atleast boundvars and placeholders when debugging the new solver do not take up excessive amounts of space.

r? @lcnr

[matthiaskrgr]

this will also change some existing ice messages, right?
please don't forget to update the corresponding tickets to match the new scheme once this lands, otherwise people may open duplicates by accident when they can't find the old tickets when searching for the update ice messages. 🙂 thanks!

[lcnr]

maybe just fn instantiate_canonical and change the first line of its doc comment to mention both placeholders and infer vars?

The function name as is feels a bit too long to me

[BoxyUwU]

@matthiaskrgr yes this could change ICE output. I'm not sure how widespread tbh, I can't remember if we ever made it so that ICE output that debug prints Ty's will actually debug print them or not. Regardless I have no idea how we would find all the ICEs out of the thousands of issues that contain old region debug output and update it. Not going to block this PR on that as that is a huge burden for simply changing printing used for debugging rustc.

[lcnr]

r=me after blessing mir opt tests and CI is green

[BoxyUwU]

@bors r=lcnr

[bors]

📌 Commit e34e344 has been approved by lcnr

It is now in the queue for this repository.

[bors]

⌛ Testing commit e34e344 with merge a385e56...

[bors]

☀️ Test successful - checks-actions
Approved by: lcnr
Pushing a385e56 to master...

[rust-timer]

Finished benchmarking commit (a385e56): comparison URL.

Overall result: ✅ improvements - no action needed

@rustbot label: -perf-regression

Instruction count

This is a highly reliable metric that was used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.2%	[-0.2%, -0.1%]	2
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	2.8%	[2.0%, 4.8%]	4
Regressions ❌ (secondary)	3.1%	[2.0%, 6.4%]	12
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	2.8%	[2.0%, 4.8%]	4

Cycles

This benchmark run did not return any relevant results for this metric.

Binary size

This benchmark run did not return any relevant results for this metric.

Bootstrap: 669.309s -> 667.729s (-0.24%)
Artifact size: 312.82 MiB -> 312.74 MiB (-0.03%)