Return a finite number of AllocIds per ConstAllocation in Miri

[saethlin]

Before this, every evaluation of a const slice would produce a new AllocId. So in Miri, this program used to have unbounded memory use:

fn main() {
    loop {
        helper();
    }
}

fn helper() {
    "ouch";
}

Every trip around the loop creates a new AllocId which we need to keep track of a base address for. And the provenance GC can never clean up that AllocId -> u64 mapping, because the AllocId is for a const allocation which will never be deallocated.

So this PR moves the logic of producing an AllocId for a ConstAllocation to the Machine trait, and the implementation that Miri provides will only produce 16 AllocIds for each allocation. The cache is also keyed on the Instance that the const is evaluated in, so that equal consts evaluated in two functions will have disjoint base addresses.

r? RalfJung

[saethlin]

@bors try @rust-timer queue

[bors]

⌛ Trying commit 29b7077 with merge 0182293...

[bors]

☀️ Try build successful - checks-actions
Build commit: 0182293 (01822939f6daaf322c811fab3c3f91d1ea582b3f)

[saethlin]

@bors try @rust-timer queue

[bors]

⌛ Trying commit c57773d with merge 8422d83...

[bors]

☀️ Try build successful - checks-actions
Build commit: 8422d83 (8422d83d697036d5904e9bb5495458979a8e5322)

[rustbot]

Failed to set assignee to ghost: invalid assignee

Note: Only org members with at least the repository "read" role, users with write permissions, or people who have commented on the PR may be assigned.

[bors]

⌛ Testing commit c8a675d with merge a3f746e...

[bors]

💔 Test failed - checks-actions

[fmease]

Error: Internal server error occurred while resolving "actions/checkout@v4". Internal server error occurred while resolving "actions/upload-artifact@v3"

@bors retry

[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)

Secret source: Actions
Prepare workflow directory
Prepare all required actions
Getting action download info
##[error]Internal server error occurred while resolving "actions/checkout@v4". Internal server error occurred while resolving "actions/upload-artifact@v3"

[saethlin]

Same error, but it looks like the queued rollup might have gotten past the flaky spot now.
@bors retry

[bors]

⌛ Testing commit c8a675d with merge 5dd57b2...

[bors]

💥 Test timed out

[RalfJung]

@bors retry

[bors]

⌛ Testing commit c8a675d with merge cd6d8f2...

[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)

[bors]

☀️ Test successful - checks-actions
Approved by: RalfJung
Pushing cd6d8f2 to master...

[rust-timer]

Finished benchmarking commit (cd6d8f2): comparison URL.

Overall result: no relevant changes - no action needed

@rustbot label: -perf-regression

Instruction count

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

Max RSS (memory usage)

Results

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)	0.5%	[0.5%, 0.5%]	1
Regressions ❌ (secondary)	4.5%	[4.4%, 4.6%]	2
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.9%	[-4.4%, -1.3%]	2
All ❌✅ (primary)	0.5%	[0.5%, 0.5%]	1

Cycles

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

Binary size

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

Bootstrap: 663.47s -> 663.194s (-0.04%)
Artifact size: 308.38 MiB -> 308.36 MiB (-0.01%)