1. A method performed by a computer system during compilation of program code for vectorizing an iterative loop of the program code for execution by a vector computer system having a plurality of processors connected to memory, wherein the memory includes one or more vector atomic memory operation (AMO) functional units and the processors include one or more vector functional units, the method comprising: scanning the program code, wherein scanning includes determining whether an operation of the iterative loop is vectorizable; if an operation is vectorizable, determining whether the operation should be executed using a vector AMO instruction in one of the vector AMO functional units; if an operation is vectorizable and the operation should be executed using a vector AMO instruction in one of the vector AMO functional units, compiling at least a portion of the operation into a vector AMO instruction; and if an operation is vectorizable and the operation should not be executed using a vector AMO instruction in one of the vector AMO functional units, compiling at least a portion of the operation to execute in one or more vector functional units of one or more processors.