Chain Constraint
ConceptA formal guidance constraint used in EPEX to ensure that consecutive instructions within a generated equivalent instruction sequence build upon each other's results, by requiring that the next instruction's source registers include the previous instruction's destination register.
First seen 6/22/2026
Last seen 6/22/2026
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Definition
The Chain Constraint is a formal guidance constraint used by EPEX when generating multi-instruction equivalent program sequences ( \hat{P}_i^j ). It is formalized in the EPEX paper as:
Definition 2 (Chain Constraint).
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1 connectionsEPEX uses the chain constraint to generate linked instruction sequences.
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[1] The chain constraint is formalized as: has_result(current_instr_p) → (rs1_{p+1} = rd_p ∨ rs2_{p+1} = rd_p), labeled Definition 2 in the EPEX paper. EPEX: Processor Verification by Equivalent Program Execution
[2] The chain constraint guides the search to produce sequences with instructions that build on each other's results, by relating register variables along the instruction sequence P_i^j indexed by position p. EPEX: Processor Verification by Equivalent Program Execution
[3] Consecutive instructions of the sequence must use the result of the previous one, if one is produced. EPEX: Processor Verification by Equivalent Program Execution
[4] The chain constraint is one of two essential constraints used to guide EPEX's formal search, alongside the Effect Constraint, to suppress uninteresting de-facto NOP variations when generating instruction sequences. EPEX: Processor Verification by Equivalent Program Execution