A system and method for simulating new instructions without compiler support for the new instructions. A simulator detects a given region in code generated by a compiler. The given region may be a candidate for vectorization or may be a region already vectorized. In response to the detection, the simulator suspends execution of a time-based simulation. The simulator then serially executes the region for at least two iterations using a functional-based simulation and using instructions with operands which correspond to P or less lanes of single-instruction-multiple-data (SIMD) execution. The value P is a maximum number of lanes of SIMD exection supported both by the compiler. The simulator stores checkpoint state during the serial execution. In response to determining no inter-iteration memory dependencies exist, the simulator returns to the time-based simulation and resumes execution using N-wide vector instructions.