Compiling for faster performance

This section describes how to use the "-fast" compiler option to analyze and optimize an entire design for improved simulation performance. This option improves performance for RTL, behavioral, and gate-level designs (See below for important information specific to gate-level designs.).

ModelSim's default mode of compilation defers module instantiations, parameter propagation, and hierarchical reference resolution until the time that a design is loaded by the simulator (see "Incremental compilation" ). This has the advantage that a design does not have to be compiled all at once, allowing independent compilation of modules without requiring knowledge of the context in which they are used.

Compiling modules independently provides flexibility to the user, but results in less efficient simulation performance in many cases. For example, the compiler must generate code for a module containing parameters as though the parameters are variables that will receive their final values when the design is loaded by the simulator. If the compiler is allowed to analyze the entire design at once, then it can determine the final values of parameters and treat them as constants in expressions, thus generating more efficient code. This is just one example of many other optimizations that require analysis of the entire design.

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