Don't fold in Instantiate when there's nothing to fold

[compiler-errors]

Maybe this helps idk

r? lcnr

[compiler-errors]

@bors2 try @rust-timer queue

[rust-bors]

⌛ Trying commit cbd67db with merge 4b9e637…

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

[compiler-errors]

i feel like ive tested this before lol

[rust-bors]

☀️ Try build successful (CI)
Build commit: 4b9e637 (4b9e63748fe7159cca76930c0864086580bb664a)

[rust-timer]

Finished benchmarking commit (4b9e637): comparison URL.

Overall result: ❌✅ regressions and improvements - please read the text below

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.

Next Steps: If you can justify the regressions found in this try perf run, please do so in sufficient writing along with @rustbot label: +perf-regression-triaged. If not, please fix the regressions and do another perf run. If its results are neutral or positive, the label will be automatically removed.

@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)	0.3%	[0.1%, 0.5%]	2
Regressions ❌ (secondary)	0.1%	[0.1%, 0.1%]	1
Improvements ✅ (primary)	-0.2%	[-0.3%, -0.2%]	4
Improvements ✅ (secondary)	-1.7%	[-3.4%, -0.1%]	12
All ❌✅ (primary)	-0.0%	[-0.3%, 0.5%]	6

Max RSS (memory usage)

Results (primary -2.1%)

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)	-	-	0
Improvements ✅ (primary)	-2.1%	[-2.1%, -2.1%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-2.1%	[-2.1%, -2.1%]	1

Cycles

Results (secondary 2.1%)

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)	3.7%	[3.6%, 3.8%]	2
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-1.2%	[-1.2%, -1.2%]	1
All ❌✅ (primary)	-	-	0

Binary size

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

Bootstrap: 755.415s -> 754.049s (-0.18%)
Artifact size: 372.14 MiB -> 372.20 MiB (0.02%)

[compiler-errors]

I think the perf wins outweigh the perf hits.

@rustbot ready

[compiler-errors]

We still fold if cfg!(debug_assertions) since the arg folder can detect out of bound arg instantiations, and that's useful in debug builds.

I believe that this is morally a debug assertion, since we never expect it in practice.

[lcnr]

instead of still folding with debug assertions, check whether the value has params.

r=me after this nit