feat(vm): refine branches with path facts - #736
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What changed? Why?
Stacked on #734 (after #733, #732, and #730).
Adds lightweight path predicates to the abstract CFG state and applies true/false assumptions on
JUMPIedges. Repeated or logically implied conditions can now be proven infeasible without enumerating concrete executions or invoking an SMT solver.Path fact domain
Refinement
ISZEROEQ, unsignedLT, and unsignedGT(value & mask) == constantfacts to the unmasked valueExpression interning is also made fully structural: equivalent expressions computed at different PCs share one
ExprId, while the arena separately records all producer sites. This is required for a later read ofCALLDATASIZE,CALLER, or an equivalent expression to reuse facts established by an earlier branch.Notes to reviewers
Key files:
crates/vm/src/core/facts.rs: constraints, assumptions, joins, implication checks, and testscrates/vm/src/core/analysis.rs: fact-bearing states and branch-specific successorscrates/vm/src/core/context.rs: contextual branch refinement and diagnosticscrates/vm/src/core/symbolic.rs: structural interning with separate producer-site trackingcrates/vm/src/core/mod.rs: exports the fact domainThis is deliberately a cheap, incomplete bit-vector domain. Signed comparisons, complex arithmetic implications, and expressions outside these rules remain unknown for the next demand-driven SMT stage.
Exploratory 100-contract run
Compared with #734 over the same first 100
largest1kcontracts:The graph is smaller because infeasible directions are removed and fewer downstream contexts are created. Structural interning accounts for the expression-count reduction. The ten-block decrease is consistent with pruning but is not yet a ground-truth precision claim. The runtime increase identifies path-fact representation and cloning as optimization targets before production migration.
How has it been tested?
cargo +nightly fmt --check --allheimdall-vmwith repository-standard allowancescargo test --workspace --lib --testslargest1kexploratory run with no failures