Move check only relevant in error case out of critical path

[estebank]

Move the check for potentially forgotten return in a tail expression
of arbitrary expressions into the coercion error branch to avoid
computing unncessary coercion checks on successful code.

Follow up to #81458.

[rust-highfive]

r? @davidtwco

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[estebank]

@bors try @rust-timer queue

[rust-timer]

Awaiting bors try build completion.

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

[bors]

⌛ Trying commit c6c243a with merge 75dfc563af3058ba1fd662a6c5c9e256e96338af...

[bors]

☀️ Try build successful - checks-actions
Build commit: 75dfc563af3058ba1fd662a6c5c9e256e96338af (75dfc563af3058ba1fd662a6c5c9e256e96338af)

[rust-timer]

Queued 75dfc563af3058ba1fd662a6c5c9e256e96338af with parent 1c77a1f, future comparison URL.

[rust-timer]

Finished benchmarking try commit (75dfc563af3058ba1fd662a6c5c9e256e96338af): comparison url.

Benchmarking this pull request likely means that it is perf-sensitive, so we're automatically marking it as not fit for rolling up. Please note that if the perf results are neutral, you should likely undo the rollup=never given below by specifying rollup- to bors.

Importantly, though, if the results of this run are non-neutral do not roll this PR up -- it will mask other regressions or improvements in the roll up.

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

[oli-obk]

@bors r+ rollup=never

I compared the perf results with #81458 and it looks to me like it fully reverts the regression

[bors]

📌 Commit c6c243a has been approved by oli-obk

[bors]

⌛ Testing commit c6c243a with merge 36aedfbed8fbd3df10ae768cd2fb7b8358420ed4...

[bors]

💥 Test timed out

[rust-log-analyzer]

A job failed! Check out the build log: (web) (plain)

Click to see the possible cause of the failure (guessed by this bot)

[JohnTitor]

@bors retry

[bors]

⌛ Testing commit c6c243a with merge dfe519b...

[bors]

☀️ Test successful - checks-actions
Approved by: oli-obk
Pushing dfe519b to master...