fix: Don't remove necessary RC instructions in DIE pass

[jfecher]

Description

Problem*

Resolves #6583

Summary*

Additional Context

Documentation*

Check one:

• No documentation needed.
• Documentation included in this PR.
• [For Experimental Features] Documentation 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 Brillig bytecode sizes

Generated at commit: b9a5af03d2f6b4e7c3a195c19077238cabfbc4b0, compared to commit: 45eb7568d56b2d254453b85f236d554232aa5df9

🧾 Summary (10% most significant diffs)

Program	Brillig opcodes (+/-)	%
nested_array_dynamic	+378 ❌	+18.98%
nested_array_in_slice	+181 ❌	+15.08%
brillig_rc_regression_6123	+24 ❌	+13.41%
nested_dyn_array_regression_5782	+15 ❌	+8.98%
regression_struct_array_conditional	+44 ❌	+8.22%
brillig_nested_arrays	+11 ❌	+6.43%

---

Full diff report 👇

Program	Brillig opcodes (+/-)	%
nested_array_dynamic	2,370 (+378)	+18.98%
nested_array_in_slice	1,381 (+181)	+15.08%
brillig_rc_regression_6123	203 (+24)	+13.41%
nested_dyn_array_regression_5782	182 (+15)	+8.98%
regression_struct_array_conditional	579 (+44)	+8.22%
brillig_nested_arrays	182 (+11)	+6.43%
fold_2_to_17	651 (+34)	+5.51%
bench_2_to_17	373 (+17)	+4.78%
poseidon2	380 (+17)	+4.68%
hashmap	21,423 (+898)	+4.38%
fold_numeric_generic_poseidon	828 (+34)	+4.28%
no_predicates_numeric_generic_poseidon	828 (+34)	+4.28%
array_sort	316 (+12)	+3.95%
array_dynamic_nested_blackbox_input	905 (+33)	+3.78%
brillig_cow	392 (+12)	+3.16%
uhashmap	13,909 (+381)	+2.82%
wildcard_type	297 (+7)	+2.41%
eddsa	10,890 (+203)	+1.90%
bigint	2,029 (+33)	+1.65%
slices	2,068 (+31)	+1.52%
regression_5252	4,723 (+69)	+1.48%
array_to_slice	830 (+12)	+1.47%
to_be_bytes	214 (+3)	+1.42%
6	1,145 (+16)	+1.42%
conditional_regression_short_circuit	1,218 (+16)	+1.33%
poseidon_bn254_hash	5,520 (+72)	+1.32%
poseidon_bn254_hash_width_3	5,520 (+72)	+1.32%
poseidonsponge_x5_254	4,323 (+54)	+1.26%
slice_regex	2,187 (+21)	+0.97%
regression_4449	735 (+6)	+0.82%
sha256	2,256 (+18)	+0.80%
ecdsa_secp256k1	909 (+6)	+0.66%
aes128_encrypt	516 (+3)	+0.58%
array_dynamic_blackbox_input	1,033 (+6)	+0.58%
conditional_1	1,200 (+6)	+0.50%
sha256_var_witness_const_regression	1,250 (+6)	+0.48%
sha2_byte	2,826 (+12)	+0.43%
regression	735 (+3)	+0.41%
sha256_var_size_regression	1,723 (+6)	+0.35%
slice_dynamic_index	2,646 (+6)	+0.23%
sha256_regression	6,580 (+12)	+0.18%
sha256_var_padding_regression	4,795 (+2)	+0.04%

[github-actions]

Changes to number of Brillig opcodes executed

Generated at commit: b9a5af03d2f6b4e7c3a195c19077238cabfbc4b0, compared to commit: 45eb7568d56b2d254453b85f236d554232aa5df9

🧾 Summary (10% most significant diffs)

Program	Brillig opcodes (+/-)	%
fold_2_to_17	+465,930 ❌	+40.63%
bench_2_to_17	+244,965 ❌	+39.66%
fold_numeric_generic_poseidon	+1,427 ❌	+26.89%
no_predicates_numeric_generic_poseidon	+1,427 ❌	+26.89%
poseidon2	+165 ❌	+22.57%

---

Full diff report 👇

Program	Brillig opcodes (+/-)	%
fold_2_to_17	1,612,665 (+465,930)	+40.63%
bench_2_to_17	862,583 (+244,965)	+39.66%
fold_numeric_generic_poseidon	6,734 (+1,427)	+26.89%
no_predicates_numeric_generic_poseidon	6,734 (+1,427)	+26.89%
poseidon2	896 (+165)	+22.57%
hashmap	65,584 (+8,861)	+15.62%
uhashmap	170,136 (+21,992)	+14.85%
brillig_rc_regression_6123	340 (+40)	+13.33%
nested_array_in_slice	1,711 (+153)	+9.82%
nested_array_dynamic	3,414 (+298)	+9.56%
nested_dyn_array_regression_5782	178 (+15)	+9.20%
brillig_nested_arrays	155 (+9)	+6.16%
regression_struct_array_conditional	1,683 (+94)	+5.92%
wildcard_type	517 (+24)	+4.87%
array_sort	614 (+28)	+4.78%
slices	3,352 (+66)	+2.01%
slice_dynamic_index	4,740 (+59)	+1.26%
brillig_cow	1,159 (+12)	+1.05%
regression_5252	967,014 (+7,884)	+0.82%
array_dynamic_nested_blackbox_input	4,551 (+30)	+0.66%
array_to_slice	1,884 (+12)	+0.64%
poseidonsponge_x5_254	193,700 (+1,230)	+0.64%
slice_regex	3,419 (+21)	+0.62%
poseidon_bn254_hash	171,817 (+864)	+0.51%
poseidon_bn254_hash_width_3	171,817 (+864)	+0.51%
eddsa	741,560 (+2,942)	+0.40%
6	7,115 (+16)	+0.23%
conditional_regression_short_circuit	7,193 (+16)	+0.22%
regression_4449	200,304 (+420)	+0.21%
sha256	13,888 (+18)	+0.13%
to_be_bytes	2,484 (+3)	+0.12%
regression	2,854 (+3)	+0.11%
conditional_1	5,735 (+6)	+0.10%
sha256_var_witness_const_regression	6,758 (+6)	+0.09%
ecdsa_secp256k1	6,787 (+6)	+0.09%
aes128_encrypt	4,486 (+3)	+0.07%
array_dynamic_blackbox_input	18,265 (+12)	+0.07%
sha256_var_size_regression	16,362 (+6)	+0.04%
sha2_byte	49,945 (+9)	+0.02%
sha256_regression	116,216 (+12)	+0.01%
sha256_var_padding_regression	219,745 (+2)	+0.00%

[github-actions]

Changes to circuit sizes

Generated at commit: b9a5af03d2f6b4e7c3a195c19077238cabfbc4b0, compared to commit: 45eb7568d56b2d254453b85f236d554232aa5df9

🧾 Summary (10% most significant diffs)

Program	ACIR opcodes (+/-)	%	Circuit size (+/-)	%
nested_array_dynamic	+161 ❌	+4.91%	+283 ❌	+2.24%
array_dynamic_nested_blackbox_input	+6 ❌	+2.43%	+17 ❌	+0.23%

---

Full diff report 👇

Program	ACIR opcodes (+/-)	%	Circuit size (+/-)	%
nested_array_dynamic	3,442 (+161)	+4.91%	12,933 (+283)	+2.24%
array_dynamic_nested_blackbox_input	253 (+6)	+2.43%	7,326 (+17)	+0.23%

[jfecher]

This PR is ready for review now - I've re-added the mutable array check optimization using array types instead of their values but unfortunately there is still a sizeable performance regression. Unsure how to fix it currently but am opening this PR if anyone wants to tackle it while I'm out next week.