1. A non-transitory computer-accessible memory medium that stores program instructions executable by a computer system to perform: providing a graphical program development environment comprising a graphical specification and constraint language that allows specification of a model of computation and explicit declaration of constraints; creating a graphical program in a graphical specification and constraint language that allows explicit declaration of constraints in response to user input, wherein the graphical program comprises: a specified model of computation; a plurality of interconnected functional blocks that visually indicate functionality of the graphical program; and graphically indicated specifications or constraints for at least one functional block of the functional blocks in the graphical program; wherein the specifications or constraints comprise: input count (IC), comprising a number of tokens consumed at an input terminal of the at least one functional block by one firing of the at least one functional block; output count (OC), comprising a number of tokens produced at an output terminal of the at least one functional block by one firing of the at least one functional block; execution time (ET), comprising a number of cycles needed by the functional block to complete firing; initiation interval (II), comprising a minimum number of cycles between firings of the functional block; input pattern (IP), comprising a sequence of Boolean values of length at most II, wherein the sequence of Boolean values aligns with the beginning of firing of the functional block, wherein each true value in the sequence denotes consumption of a token by the functional block; and output pattern (OP), comprising a sequence of Boolean values of length at most II, wherein the sequence of Boolean values aligns with the end of firing of the functional block, wherein each true value in the sequence denotes production of a token by the functional block; and analyzing the graphical program, including the specifications or constraints, thereby generating analysis results regarding performance or resource utilization, wherein said analyzing is performed before conversion of the graphical program to a hardware description, and wherein said analyzing comprises: estimating performance or resource utilization for the at least one functional block, the plurality of functional blocks, or the graphical program, using a plurality of models, wherein each model has an associated level of granularity, and comprises raw model data and a function to customize the model for said estimating; reporting whether or not the specifications or constraints are met based on the analysis results; changing a first model of the plurality of models to a second model based on said reporting, wherein the second model has a different level of granularity from that of the first model; repeating said analyzing and said reporting one or more times; and automatically generating a program based on the graphical program, wherein the program implements the functionality of the graphical program in accordance with the specified model of computation, and further implements the specifications or constraints; wherein the program is useable to configure a programmable hardware element to perform the functionality subject to the specifications or constraints.