Remove box syntax from rustc_mir_dataflow and rustc_mir_transform

[est31]

Continuation of #87781, inspired by #97239. The usages that this PR removes have not appeared from nothing, instead the usage in rustc_mir_dataflow and rustc_mir_transform was from #80522 which split up rustc_mir, and which was filed before I filed #87781, so it was using the state from before my PR. But it was merged after my PR was merged, so the box_syntax uses were able to survive here. Outside of this introduction due to the code being outside of the master branch at the point of merging of my PR, there was only one other introduction of box syntax, in #95159. That box syntax was removed again though in #95555. Outside of that, box_syntax has not made its reoccurrance in compiler crates.

[rust-highfive]

r? @compiler-errors

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[est31]

Also, maybe it would be a good idea to do a perf run, but I doubt there is going to be much of an impact. #87781 didn't have any outside of a very minor regression for rustdoc close to the noise limit, that was then reverted.

[compiler-errors]

@bors try @rust-timer queue

[rust-timer]

Awaiting bors try build completion.

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

[bors]

⌛ Trying commit 99603ef with merge 454eb7ecb0429d36f9d0367d02449abb1f7b38f9...

[compiler-errors]

didn't realize this PR was so small, lol. Started that perf after just looking at the description.

anyways r=me if that perf run comes back clean.

[bors]

☀️ Try build successful - checks-actions
Build commit: 454eb7ecb0429d36f9d0367d02449abb1f7b38f9 (454eb7ecb0429d36f9d0367d02449abb1f7b38f9)

[rust-timer]

Queued 454eb7ecb0429d36f9d0367d02449abb1f7b38f9 with parent 4bb4dc4, future comparison URL.

[rust-timer]

Finished benchmarking commit (454eb7ecb0429d36f9d0367d02449abb1f7b38f9): comparison url.

Instruction count

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

Max RSS (memory usage)

Results

• Primary benchmarks: no relevant changes found
• Secondary benchmarks: 🎉 relevant improvements found

	Regressions 😿 (primary)	Regressions 😿 (secondary)	Improvements 🎉 (primary)	Improvements 🎉 (secondary)	All 😿 🎉 (primary)
count1	0	0	0	2	0
mean2	N/A	N/A	N/A	-1.6%	N/A
max	N/A	N/A	N/A	-2.0%	N/A

Cycles

Results

• Primary benchmarks: 🎉 relevant improvements found
• Secondary benchmarks: no relevant changes found

	Regressions 😿 (primary)	Regressions 😿 (secondary)	Improvements 🎉 (primary)	Improvements 🎉 (secondary)	All 😿 🎉 (primary)
count1	0	0	2	0	2
mean2	N/A	N/A	-2.1%	N/A	-2.1%
max	N/A	N/A	-2.2%	N/A	-2.2%

If you disagree with this performance assessment, please file an issue in rust-lang/rustc-perf.

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-review -S-waiting-on-perf -perf-regression

Footnotes

1. number of relevant changes ↩ ↩²

2. the arithmetic mean of the percent change ↩ ↩²

[compiler-errors]

@bors r+

[bors]

📌 Commit 99603ef has been approved by compiler-errors

[bors]

⌛ Testing commit 99603ef with merge b2eed72...

[bors]

☀️ Test successful - checks-actions
Approved by: compiler-errors
Pushing b2eed72 to master...

[rust-timer]

Finished benchmarking commit (b2eed72): comparison url.

Instruction count

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

Max RSS (memory usage)

Results

• Primary benchmarks: 😿 relevant regression found
• Secondary benchmarks: mixed results

	Regressions 😿 (primary)	Regressions 😿 (secondary)	Improvements 🎉 (primary)	Improvements 🎉 (secondary)	All 😿 🎉 (primary)
count1	1	3	0	1	1
mean2	3.7%	1.7%	N/A	-3.7%	3.7%
max	3.7%	1.9%	N/A	-3.7%	3.7%

Cycles

Results

• Primary benchmarks: mixed results
• Secondary benchmarks: no relevant changes found

	Regressions 😿 (primary)	Regressions 😿 (secondary)	Improvements 🎉 (primary)	Improvements 🎉 (secondary)	All 😿 🎉 (primary)
count1	2	0	1	0	3
mean2	2.0%	N/A	-3.3%	N/A	0.2%
max	2.6%	N/A	-3.3%	N/A	-3.3%

If you disagree with this performance assessment, please file an issue in rust-lang/rustc-perf.

@rustbot label: -perf-regression

Footnotes

1. number of relevant changes ↩ ↩²

2. the arithmetic mean of the percent change ↩ ↩²