(feat): Added tracking on enums as part of equality analysis

[eytan-starkware]

Summary

Enhances the equality analysis to track enum constructs and match relationships. The analysis now maintains a hashcons for enum variants, allowing it to detect when two enum constructs with the same variant and equivalent inputs should produce equivalent outputs. This enables more precise tracking of enum values across branches and through match statements.

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Type of change

Please check one:

• Bug fix (fixes incorrect behavior)
• New feature
• Performance improvement
• Documentation change with concrete technical impact
• Style, wording, formatting, or typo-only change

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Why is this change needed?

The equality analysis previously didn't track relationships between enum variants and their inner values. This limited the optimizer's ability to detect equivalent enum values and perform optimizations across match statements and branches. By tracking these relationships, we can enable more aggressive optimizations for code that uses enums.

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What was the behavior or documentation before?

The equality analysis would not track relationships between enum variants and their inner values. When an enum was constructed or matched against, this information was lost, preventing optimizations that depend on knowing the relationship between the enum and its contents.

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What is the behavior or documentation after?

The equality analysis now:

• Tracks enum constructs via a hashcons mechanism
• Preserves enum relationships across branches when the same variant is used
• Recognizes when a match arm extracts a value that was previously used to construct the enum
• Properly handles the merging of enum information at control flow join points

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Additional context

This is part of ongoing work to improve the optimizer's ability to reason about higher-level constructs in Cairo. The implementation uses both forward and reverse mappings to efficiently track enum relationships in both directions.

[reviewable-StarkWare]

This change is 

[eytan-starkware]

• (feat): Added tracking structs as part of equality analysis #9646
• (feat): Added tracking on enums as part of equality analysis #9645 👈 (View in Graphite)
• feat: Dataflow forward equality analysis #9597
• (feat): Creating forward analysis for the dataflow framework #9584 : 1 other dependent PR (#9585 )
• (refactor): Updating analysis framework to be easier to use #9564 : 1 other dependent PR (#9534 )
• main

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[orizi]

@orizi reviewed all commit messages and made 1 comment.
Reviewable status: 0 of 3 files reviewed, 2 unresolved discussions (waiting on @eytan-starkware and @TomerStarkware).

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crates/cairo-lang-lowering/src/analysis/equality_analysis.rs line 91 at r1 (raw file):

    enum_hashcons: OrderedHashMap<(ConcreteVariant<'db>, VariableId), VariableId>,

    /// Reverse hashcons for enum constructs: maps (variant, output_rep) -> input_rep.

the maps seem the opposite.

Code quote:

(variant, output_rep) -> input_rep.

[eytan-starkware]

@eytan-starkware made 2 comments.
Reviewable status: 0 of 3 files reviewed, 2 unresolved discussions (waiting on @orizi and @TomerStarkware).

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crates/cairo-lang-lowering/src/analysis/equality_analysis.rs line 91 at r1 (raw file):

Previously, orizi wrote…

the maps seem the opposite.

Bad comment. Fixed.

[orizi]

@orizi reviewed all commit messages, made 1 comment, and resolved 1 discussion.
Reviewable status: 0 of 4 files reviewed, 2 unresolved discussions (waiting on eytan-starkware and TomerStarkware).

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crates/cairo-lang-lowering/src/analysis/equality_analysis.rs line 1 at r3 (raw file):

//! Equality analysis for lowered IR.

this entire file already existed - right?

[eytan-starkware]

@eytan-starkware made 1 comment.
Reviewable status: 0 of 4 files reviewed, 2 unresolved discussions (waiting on orizi and TomerStarkware).

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crates/cairo-lang-lowering/src/analysis/equality_analysis.rs line 1 at r3 (raw file):

Previously, orizi wrote…

this entire file already existed - right?

Correct. Rebased.

[orizi]

@orizi reviewed 1 file and all commit messages, made 1 comment, and resolved 1 discussion.
Reviewable status: 1 of 4 files reviewed, 2 unresolved discussions (waiting on eytan-starkware and TomerStarkware).

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crates/cairo-lang-lowering/src/analysis/equality_analysis.rs line 511 at r4 (raw file):

                {
                    let matched_var = enum_info.input.var_id;
                    let arm_var = arm.var_ids[0];

Suggestion:

                    && let MatchArmSelector::VariantId(variant) = arm.arm_selector
                    && let [arm_var] = &arm.var_ids
                {
                    let matched_var = enum_info.input.var_id;

[eytan-starkware]

@eytan-starkware made 1 comment and resolved 1 discussion.
Reviewable status: 1 of 4 files reviewed, 1 unresolved discussion (waiting on orizi and TomerStarkware).

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crates/cairo-lang-lowering/src/analysis/equality_analysis.rs line 511 at r4 (raw file):

                {
                    let matched_var = enum_info.input.var_id;
                    let arm_var = arm.var_ids[0];

Done.

[orizi]

@orizi reviewed 3 files and all commit messages, and made 1 comment.
Reviewable status: all files reviewed, 2 unresolved discussions (waiting on eytan-starkware and TomerStarkware).

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crates/cairo-lang-lowering/src/analysis/equality_analysis.rs line 263 at r5 (raw file):

        for (&(variant, input), &output) in self.enum_hashcons.iter() {
            let name = variant.id.name(db).to_string(db);
            lines.push(format!("{}({}) = {}", name, v(input), v(output)));

Suggestion:

            let name = variant.id.name(db).to_string(db);
            lines.push(format!("{name}({}) = {}", v(input), v(output)));

[eytan-starkware]

@eytan-starkware made 1 comment.
Reviewable status: 3 of 4 files reviewed, 2 unresolved discussions (waiting on orizi and TomerStarkware).

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crates/cairo-lang-lowering/src/analysis/equality_analysis.rs line 263 at r5 (raw file):

        for (&(variant, input), &output) in self.enum_hashcons.iter() {
            let name = variant.id.name(db).to_string(db);
            lines.push(format!("{}({}) = {}", name, v(input), v(output)));

Done.

[orizi]

@orizi reviewed 1 file and all commit messages, made 1 comment, and resolved 2 discussions.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on TomerStarkware).