(optimization): Reboxing now also works on whole var reboxing

[eytan-starkware]

Enhances the reboxing optimization to support whole variable reboxing, eliminating unnecessary box/unbox operations.

What changed?

• Refactored the apply_reboxing_candidate function to support for the ReboxingValue::Unboxed case, which represents whole variable reboxing
• Implemented a new replace_variable_usages function that replaces all usages of the reboxed with the original box variable throughout the lowered function
• Extracted the existing member-of-unboxed logic into a separate replace_into_box_call function
• Updated tests to verify the new functionality

[reviewable-StarkWare]

This change is 

[eytan-starkware]

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• (optimization): Reboxing now also works on whole var reboxing #8994 👈 (View in Graphite)
• (optimization): Reboxing also applied on Box of snapshots #8954
• (optimization): automatically detecting reboxing of struct member and applying struct_box_deconstruct libfunc #8768
• main

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[orizi]

@orizi reviewed all commit messages.
Reviewable status: 0 of 2 files reviewed, 1 unresolved discussion (waiting on @eytan-starkware, @giladchase, and @ilyalesokhin-starkware)

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crates/cairo-lang-lowering/src/optimizations/reboxing.rs line 268 at r1 (raw file):

/// Replaces all usages of old_var with new_var throughout the lowered function.
fn replace_variable_usages(lowered: &mut Lowered<'_>, old_var: VariableId, new_var: VariableId) {

can't you use VarRemapper to do all candidate replacements in one go?

[eytan-starkware]

Reviewable status: 0 of 2 files reviewed, 1 unresolved discussion (waiting on @giladchase, @ilyalesokhin-starkware, and @orizi)

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crates/cairo-lang-lowering/src/optimizations/reboxing.rs line 268 at r1 (raw file):

Previously, orizi wrote…

can't you use VarRemapper to do all candidate replacements in one go?

Yes, much better

[orizi]

@orizi reviewed 2 of 2 files at r2, all commit messages.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @eytan-starkware, @giladchase, and @ilyalesokhin-starkware)

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crates/cairo-lang-lowering/src/optimizations/reboxing.rs line 205 at r2 (raw file):

    // We sort the candidates such that removal of statements can be done in reverse order.
    stmts_to_remove.sort_by_key(|(block_id, stmt_idx)| (block_id.0, *stmt_idx));

was there any order to the original candidates? or these are basically random?

[eytan-starkware]

Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @giladchase, @ilyalesokhin-starkware, and @orizi)

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crates/cairo-lang-lowering/src/optimizations/reboxing.rs line 205 at r2 (raw file):

Previously, orizi wrote…

was there any order to the original candidates? or these are basically random?

I think it is safe to assume they were ordered correctly ahead of time, so reversing directly should be safe, but I dont want to add that assumption. I can use unstable sort if performance is an issue, but I expect this to be a small amount of statements to remove

[orizi]

Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @eytan-starkware, @giladchase, and @ilyalesokhin-starkware)

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crates/cairo-lang-lowering/src/optimizations/reboxing.rs line 205 at r2 (raw file):

Previously, eytan-starkware wrote…

I think it is safe to assume they were ordered correctly ahead of time, so reversing directly should be safe, but I dont want to add that assumption. I can use unstable sort if performance is an issue, but I expect this to be a small amount of statements to remove

do stable - and doc that it should be sorted already.
i just don't want it to overly kill large auto-generated codes.

[eytan-starkware]

Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @giladchase, @ilyalesokhin-starkware, and @orizi)

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crates/cairo-lang-lowering/src/optimizations/reboxing.rs line 205 at r2 (raw file):

Previously, orizi wrote…

do stable - and doc that it should be sorted already.
i just don't want it to overly kill large auto-generated codes.

Done.

[orizi]

@orizi reviewed 1 of 1 files at r3, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @giladchase and @ilyalesokhin-starkware)

[orizi]

@orizi reviewed 1 of 1 files at r4, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @giladchase and @ilyalesokhin-starkware)