Fix printing regions with -Z verbose

[RalfJung]

When dumping MIR with -Z verbose, it would print regions on types, but not in the code. It seems the Rvalue printing code tried to be smart and guessed when the Display for Region would not possibly print anything.

This PR makes it no longer be smart, and just always use the Display like all the other code (e.g. printing types) does.

[rust-highfive]

r? @nikomatsakis

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[arielb1]

[00:50:24] failures:

[00:50:24]     [mir-opt] mir-opt/storage_live_dead_in_statics.rs

This is a real output change - now e.g. a borrow for static lifetime displays as &'static x even without -Z verbose. I think you should just use -Z verbose -Z identify-regions.

[RalfJung]

This is a real output change - now e.g. a borrow for static lifetime displays as &'static x even without -Z verbose.

Ah, indeed. I did not realize this. I will push a patch which just changes the conditional to be verbose || identify-regions.

I think you should just use -Z verbose -Z identify-regions.

At the very least, then the documentation of identify-regions needs changing.

I generally find it rather strange that verbose would enable regions in some places and identify-regions in others, and only the combination gives you regions everyhwere. I guess another option would be to make region printing tied to identify-regions only, and ignore verbose?

[RalfJung]

CI failure looks like network problem.

[arielb1]

@bors r+ rollup

[bors]

📌 Commit 4e1249d has been approved by arielb1

[RalfJung]

Thanks :)

[nikomatsakis]

@bors r+

[bors]

💡 This pull request was already approved, no need to approve it again.

• There's another pull request that is currently being tested, blocking this pull request: Bump master to 1.21.0 #43320

[bors]

📌 Commit 4e1249d has been approved by nikomatsakis