Use stable metric for const eval limit instead of current terminator-based logic

[bryangarza]

This patch adds a MirPass that inserts a new MIR instruction ConstEvalCounter to any loops and function calls in the CFG. This instruction is used during Const Eval to count against the const_eval_limit, and emit the StepLimitReached error, replacing the current logic which uses Terminators only.

The new method of counting loops and function calls should be more stable across compiler versions (i.e., not cause crates that compiled successfully before, to no longer compile when changes to the MIR generation/optimization are made).

Also see: #103877

[rustbot]

r? @Nilstrieb

(rustbot has picked a reviewer for you, use r? to override)

[bryangarza]

r? @pnkfelix

[bryangarza]

Remaining:

• use checked_add(..) for incrementing counter
• Make use of StepLimitReached error and remove terminator-based logic from https://github.com/rust-lang/rust/blame/master/compiler/rustc_const_eval/src/const_eval/machine.rs#L564-L576
• Rebase

[bryangarza]

@rustbot ready

[rustbot]

Some changes occurred to the CTFE / Miri engine

cc @rust-lang/miri

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

Some changes occurred in compiler/rustc_codegen_cranelift

cc @bjorn3

This PR changes MIR

cc @oli-obk, @RalfJung, @JakobDegen, @davidtwco, @celinval, @vakaras

[rustbot]

Some changes occurred in src/tools/clippy

cc @rust-lang/clippy

[bryangarza]

@rustbot ready

[bryangarza]

@rustbot ready

[oli-obk]

@bors r+

[bors]

📌 Commit bdb815a has been approved by oli-obk

It is now in the queue for this repository.

[bors]

⌛ Testing commit bdb815a with merge 3cdd019...

[bors]

☀️ Test successful - checks-actions
Approved by: oli-obk
Pushing 3cdd019 to master...

[rust-timer]

Finished benchmarking commit (3cdd019): comparison URL.

Overall result: ❌ regressions - ACTION NEEDED

Next Steps: If you can justify the regressions found in this perf run, please indicate this with @rustbot label: +perf-regression-triaged along with sufficient written justification. If you cannot justify the regressions please open an issue or create a new PR that fixes the regressions, add a comment linking to the newly created issue or PR, and then add the perf-regression-triaged label to this PR.

@rustbot label: +perf-regression
cc @rust-lang/wg-compiler-performance

Instruction count

This is a highly reliable metric that was used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	0.3%	[0.3%, 0.4%]	3
Regressions ❌ (secondary)	0.8%	[0.5%, 1.0%]	9
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.3%	[0.3%, 0.4%]	3

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)	2.3%	[2.3%, 2.3%]	1
Regressions ❌ (secondary)	2.0%	[1.8%, 2.2%]	2
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	2.3%	[2.3%, 2.3%]	1

Cycles

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
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.4%	[-2.4%, -2.4%]	1
All ❌✅ (primary)	-	-	0

[oli-obk]

This small regression is expected. We do some extra work for all CTFE code to insert the new statements. Compared to not doing any work before, even if a very small change, it is still visible on some tests.

[pnkfelix]

I agree with @oli-obk 's comment above

@rustbot label: +perf-regression-triaged