Cmpconst

Cmpconst is a term used in programming and compiler literature to describe the operation of comparing a runtime value against a compile-time constant. It denotes the primitive where a value is tested for equality or an ordering relation with a fixed, known value, yielding a boolean result used to drive conditional branches, pattern matching, or decision logic.

In compiler design, cmpconst-like checks are central to optimizations such as constant folding, where expressions involving constants are evaluated at compile time, and to branch analysis, where the compiler decides between different control-flow paths based on a constant threshold or value. Many intermediate representations expose this primitive in the form of comparisons against immediate constants, which enables efficient generation of machine code and jump tables.

In low-level code, a comparison against a constant is typically realized as a compare instruction followed by a conditional branch. For example, a high-level condition like x == 5 is lowered to a compare against the immediate value 5 and a subsequent conditional jump. The exact semantics and available predicates depend on the language, IR, or target architecture, including considerations for signed versus unsigned comparisons and potential overflows.

Limitations and caveats include handling of edge cases such as overflow, signedness, and range constraints, which affect optimization results and correctness. While the term cmpconst appears in various manuals and educational materials, it is not universally standardized and is often described in context as a common pattern for testing values against constants.

See also: comparison operators, constant propagation, constant folding, branch instructions, icmp/cmp in intermediate representations.