fix(ACIR): check vector length is not zero before pop_front

[asterite]

Description

Problem

Resolves https://github.com/noir-lang/noir/security/advisories/GHSA-h47v-w5hw-q4x3

Summary

Additional Context

User Documentation

Check one:

• No user documentation needed.
• Changes in docs/ included in this PR.
• [For Experimental Features] Changes in docs/ to be submitted in a separate PR.

PR Checklist

• I have tested the changes locally.
• I have formatted the changes with Prettier and/or cargo fmt on default settings.

[github-actions]

Changes to circuit sizes

Generated at commit: 26377a028302909774ceb6276e7a95d1d299b363, compared to commit: da063950925eade6172da1ed5910c2ef0a8127ff

🧾 Summary (10% most significant diffs)

Program	ACIR opcodes (+/-)	%	Circuit size (+/-)	%
vector_dynamic_index	+3 ❌	+0.38%	+2 ❌	+0.04%
regression_9593	+2 ❌	+11.11%	+1 ❌	+0.04%

---

Full diff report 👇

Program	ACIR opcodes (+/-)	%	Circuit size (+/-)	%
vector_dynamic_index	801 (+3)	+0.38%	5,158 (+2)	+0.04%
regression_9593	20 (+2)	+11.11%	2,836 (+1)	+0.04%

[github-actions]

⚠️ Performance Alert ⚠️

Possible performance regression was detected for benchmark 'Test Suite Duration'.
Benchmark result of this commit is worse than the previous benchmark result exceeding threshold 1.20.

Benchmark suite	Current: 3240f52	Previous: 1d4b60b	Ratio
test_report_zkpassport_noir-ecdsa_	2 s	1 s	2

This comment was automatically generated by workflow using github-action-benchmark.

CC: @TomAFrench

[github-actions]

⚠️ Performance Alert ⚠️

Possible performance regression was detected for benchmark 'Execution Time'.
Benchmark result of this commit is worse than the previous benchmark result exceeding threshold 1.20.

Benchmark suite	Current: da67f30	Previous: 79e93d8	Ratio
rollup-block-root-single-tx	0.003 s	0.002 s	1.50
rollup-checkpoint-merge	0.004 s	0.003 s	1.33
rollup-root	0.005 s	0.004 s	1.25

This comment was automatically generated by workflow using github-action-benchmark.

CC: @TomAFrench

[github-actions]

⚠️ Performance Alert ⚠️

Possible performance regression was detected for benchmark 'ACVM Benchmarks'.
Benchmark result of this commit is worse than the previous benchmark result exceeding threshold 1.20.

Benchmark suite	Current: da67f30	Previous: 79e93d8	Ratio
perfectly_parallel_batch_inversion_opcodes	2791165 ns/iter (± 3117)	2262216 ns/iter (± 3305)	1.23

This comment was automatically generated by workflow using github-action-benchmark.

CC: @TomAFrench

[asterite]

It seems moving the fix to ssagen leads to worse performance than just adding the check in ACIR.

[vezenovm]

It seems moving the fix to ssagen leads to worse performance than just adding the check in ACIR.

regression_10446 which has the largest ACIR opcodes regression only uses pop_back. We have this vector length check inside of ACIR gen for pop_back so it means we are now doing a redundant check.

[jfecher]

I'm alright with fixing this first and worrying about optimizations later unless it'd be trivial to improve

[vezenovm]

I'm alright with fixing this first and worrying about optimizations later unless it'd be trivial to improve

It should just be removal from ACIR gen.

@asterite I am realizing now though that someone could write a malicious SSA though that does not include these checks. We probably would need to move all these checks (for remove and insert as well) to an SSA pass similar to expand_signed_math for safety. For now, to get the fix in I guess we can just go back to the original assertion within ACIR. Apologies for the back and forth here.

In a follow-up, we could have these checks included by an SSA pass so that we do not have repeated logic for Brillig gen and ACIR gen.

[asterite]

@vezenovm All good! I had to leave for a while so I couldn't revert the last PR, otherwise I would have as soon as I saw those regressions :-)

[github-actions]

⚠️ Performance Alert ⚠️

Possible performance regression was detected for benchmark 'Brillig Execution Time'.
Benchmark result of this commit is worse than the previous benchmark result exceeding threshold 1.20.

Benchmark suite	Current: 3240f52	Previous: 1d4b60b	Ratio
rollup-block-root-single-tx	0.003 s	0.002 s	1.50

This comment was automatically generated by workflow using github-action-benchmark.

CC: @TomAFrench