Remove DepKind::CrateMetadata and pre-allocation of DepNodes

[tgnottingham]

Remove much of the special-case handling around crate metadata
dependency tracking by replacing DepKind::CrateMetadata and the
pre-allocation of corresponding DepNodes with on-demand invocation
of the crate_hash query.

[rust-highfive]

r? @lcnr

(rust-highfive has picked a reviewer for you, use r? to override)

[tgnottingham]

@rustbot label T-compiler A-incr-comp

r? @michaelwoerister

[tgnottingham]

This also removes an optimization around registration of the crate metadata dependency, but I'm happy to add it back if necessary. Locally, the perf impact seemed to be small, so I think the simplification may be worth it.

This also relates to logic affecting #62649. That issue has a lot of confusion around it, and this change will help make reasoning about it easier. I will follow-up with that issue at some point.

[Aaron1011]

@bors try @rust-timer queue

[rust-timer]

Awaiting bors try build completion.

[bors]

⌛ Trying commit a3c3735cefaf039ec7f45e46f858ba2d641c5138 with merge a9d18ad03c95138870091e989d84f332af0a0b23...

[rust-log-analyzer]

The job mingw-check failed! Check out the build log: (web) (plain)

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

configure: rust.channel         := nightly
configure: rust.debug-assertions := True
configure: llvm.assertions      := True
configure: dist.missing-tools   := True
configure: build.configure-args := ['--enable-sccache', '--disable-manage-submodu ...
configure: writing `config.toml` in current directory
configure: 
configure: run `python /checkout/x.py --help`
configure: 
---
skip untracked path cpu-usage.csv during rustfmt invocations
skip untracked path src/doc/book/ during rustfmt invocations
skip untracked path src/doc/rust-by-example/ during rustfmt invocations
skip untracked path src/llvm-project/ during rustfmt invocations
Diff in /checkout/compiler/rustc_middle/src/ty/context.rs at line 37:
 use rustc_errors::ErrorReported;
 use rustc_hir as hir;
 use rustc_hir::def::{DefKind, Res};
-use rustc_hir::def_id::{CrateNum, DefId, DefIdMap, LocalDefId};
 use rustc_hir::def_id::LOCAL_CRATE;
+use rustc_hir::def_id::{CrateNum, DefId, DefIdMap, LocalDefId};
 use rustc_hir::intravisit::Visitor;
 use rustc_hir::intravisit::Visitor;
 use rustc_hir::lang_items::LangItem;
Running `"/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/rustfmt" "--config-path" "/checkout" "--edition" "2018" "--unstable-features" "--skip-children" "--check" "/checkout/compiler/rustc_middle/src/ty/context.rs"` failed.
If you're running `tidy`, try again with `--bless`. Or, if you just want to format code, run `./x.py fmt` instead.
Build completed unsuccessfully in 0:00:18

[tgnottingham]

I really need to automate x.py fmt.

[cjgillot]

The command seems to have been lost.
@bors try @rust-timer queue

[rust-timer]

Awaiting bors try build completion.

[bors]

⌛ Trying commit ef71435e28c6743397d22957685a397b1e419da7 with merge 6da8d0299f5b2280b306e89ebfd7cb6902fcab5f...

[bors]

☀️ Try build successful - checks-actions
Build commit: 6da8d0299f5b2280b306e89ebfd7cb6902fcab5f (6da8d0299f5b2280b306e89ebfd7cb6902fcab5f)

[rust-timer]

Queued 6da8d0299f5b2280b306e89ebfd7cb6902fcab5f with parent 929f66a, future comparison URL.

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

[rust-timer]

Finished benchmarking try commit (6da8d0299f5b2280b306e89ebfd7cb6902fcab5f): 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

[tgnottingham]

Perf is neutral, which is good.

[michaelwoerister]

Interesting idea! I hope I'll be able to review this next week.

[cjgillot]

This PR effectively replaces the creation of a dedicated DepNode for each crate by using the DepNode corresponding to the crate_hash query. Since the former behaviour based the greenness of the crate DepNode on this very crate_hash, there should be no change in the incremental behaviour.

[tgnottingham]

Addressed comments and rebased to fix a conflict.

[bors]

☔ The latest upstream changes (presumably #78452) made this pull request unmergeable. Please resolve the merge conflicts.

[michaelwoerister]

This is a great find, @tgnottingham! It lets us get rid of quite a bit of special casing indeed. r=me with the comment below addressed.

[bors]

☔ The latest upstream changes (presumably #80463) made this pull request unmergeable. Please resolve the merge conflicts.

[tgnottingham]

Thank you for the review @michaelwoerister! Addressed your comments.

[pnkfelix]

@bors r=michaelwoerister

[bors]

📌 Commit 8e7cbc2 has been approved by michaelwoerister

[bors]

⌛ Testing commit 8e7cbc2 with merge fcbd305...

[bors]

☀️ Test successful - checks-actions
Approved by: michaelwoerister
Pushing fcbd305 to master...