Optimize initialization of mostly zeroed aggregates

[vaivaswatha]

^{Cursor Bugbot found 1 potential issue for commit 101734d}

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PR Summary

Medium Risk
Touches IR lowering logic and instruction ordering for aggregate initialization; incorrect zero detection or insertion position could cause miscompilations or missed lowering (as evidenced by updated failing snapshot).

Overview
Adds a new init_aggr lowering optimization: when an aggregate is mostly runtime-zeroed (>= ~30% by byte size), it now emits a mem_clear_val for the whole aggregate and then stores only the non-zero fields, including recursive handling of nested init_aggrs and careful insertion ordering.

Extends lowering plumbing with InitAggrInitializer::is_runtime_zeroed() and a skip_zeroes flag to avoid redundant zero stores (and disables the repeat-array fast path when zero-skipping would route through temporaries). Updates/adds IR generation tests and several e2e snapshots; also updates an auto contract ID, and the const_of_contract_call snapshot now captures a failing case where InstOp::InitAggr was not lowered.

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Cursor Bugbot has reviewed your changes and found 1 potential issue.

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Skipping zero initializers leaves nested init_aggr instructions unlowered

High Severity

When skip_zeroes is true and an initializer passes the is_runtime_zeroed check, the code uses continue to skip the call to lower_single_initializer_to_stores. However, if the initializer is a NestedInitAggr, this skips the critical cleanup code that removes the nested init_aggr instruction from the IR. Since nested init_aggrs are excluded from find_root_init_aggrs, they aren't removed at the end of the pass either. This leaves unlowered InitAggr instructions in the IR, causing the "InstOp::InitAggr was not lowered" compiler errors shown in the test failures for cases like [0], (0,), and S1 { a: 0 }.

Additional Locations (1)

• sway-ir/src/optimize/init_aggr_lowering.rs#L470-L474

 

[ironcev]

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