Skip walking into param-env component if it has no placeholder/re-var

[compiler-errors]

Although it only provides a minor perf improvement, it seems like it could matter in more pathological cases.

[compiler-errors]

@bors2 try @rust-timer queue

[rust-bors]

⌛ Trying commit e13757e with merge e3ecd5f…

To cancel the try build, run the command @bors2 try cancel.

[rust-bors]

☀️ Try build successful (CI)
Build commit: e3ecd5f (e3ecd5f5fd02f50bc278c1f0cd5b4dbd9e07242a, parent: 6dec76f1c2809fded082dd44d3752d3f6220d767)

[rust-timer]

Finished benchmarking commit (e3ecd5f): comparison URL.

Overall result: ❌✅ regressions and improvements - no action needed

Benchmarking this pull request means it may be perf-sensitive – we'll automatically label it not fit for rolling up. You can override this, but we strongly advise not to, due to possible changes in compiler perf.

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

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	0.0%	[0.0%, 0.0%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.5%	[-0.5%, -0.5%]	3
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

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

Cycles

Results (secondary 0.2%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	2.4%	[2.4%, 2.4%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.0%	[-2.0%, -2.0%]	1
All ❌✅ (primary)	-	-	0

Binary size

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

Bootstrap: 461.008s -> 461.232s (0.05%)
Artifact size: 372.14 MiB -> 372.18 MiB (0.01%)

[compiler-errors]

r? lcnr

[lcnr]

why only RE_INFER instead of full infer?

[compiler-errors]

bc we only care about infer regions in this folder's logic -- it would not even be necessary if we didn't replace free regions with infer

[compiler-errors]

why would we care about ty/ct infer for this folder anyways? 🤔

[lcnr]

we only care as in: there should never be infer types/consts in the param_env 😁 if we end up with a ty var for whatever reason, then this folder would start incorrectly treating (): Trait<?x> as global evne though it shouldn't be. It currently detects ambiguous aliases in the env as global

[compiler-errors]

I don't see how that is the case and how this behavior would change with this fast path, given that visit_ty does not care about infer types at all and because structurally_normalize_ty just returns Ok(_) for infer types.

Can you explain in more detail, because I am obviously missing something here?