Although numerous loop optimization techniques have been designed and deployed in commercial compilers in the past, virtually no common experimental infrastructure nor repository exists to help the compiler community evaluate the effectiveness of these techniques. This paper describes a repository, LORE, that maintains a large number of C language for loop nests extracted from popular benchmarks, libraries, and real applications. It also describes the infrastructure that builds and maintains the repository. Each loop nest in the repository has been compiled, transformed, executed, and measured independently. These loops cover a variety of properties that can be used by the compiler community to evaluate loop optimizations using a broad and representative collection of loops. To illustrate the usefulness of the repository, we also present two example applications. One is assessing the capabilities of the auto-vectorization features of three widely used compilers. The other is measuring the performance difference of a compiler across different versions. These applications prove that the repository is valuable for identifying the strengths and weaknesses of a compiler and for quantitatively measuring the evolution of a compiler.