Folder experiment: Account for flags in ArgFolder

[compiler-errors]

NOTE: This is one of a series of perf experiments that I've come up with while sick in bed. I'm assigning them to lqd b/c you're a good reviewer and you'll hopefully be awake when these experiments finish, lol.

r? lqd

The arg folder is very hot and this hopefully avoids unnecessarily substituting predicates and consts when they have no consts in them :>

[compiler-errors]

@bors try @rust-timer queue

[bors]

⌛ Trying commit fa912f4 with merge 723e1f0...

[bors]

☀️ Try build successful - checks-actions
Build commit: 723e1f0 (723e1f0b0c4b4dde0bc5e20f3799217b793cd1bc)

[rust-timer]

Finished benchmarking commit (723e1f0): comparison URL.

Overall result: no relevant changes - no action needed

Benchmarking this pull request likely means that it is perf-sensitive, so we're automatically marking it as not fit for rolling up. While you can manually mark this PR as fit for rollup, we strongly recommend not doing so since this PR may lead to changes in compiler perf.

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

Instruction count

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

Max RSS (memory usage)

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

Cycles

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

Binary size

Results (primary -0.0%)

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)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.0%	[-0.0%, -0.0%]	4
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-0.0%	[-0.0%, -0.0%]	4

Bootstrap: 777.539s -> 776.567s (-0.13%)
Artifact size: 365.91 MiB -> 365.90 MiB (-0.00%)

[lqd]

Interesting that this is neutral 🤔

[compiler-errors]

nooooo i thought this one would be fire