ansi-test

run this on and off for many billions of iterations on desktop and laptop machines on various CL implementations, now mainly on SBCL. Most of the test input reduction is handled automatically, which is a big help. (2) Generate random possibly invalid code by mutating or recombining snippets drawn from a large corpus of code, to see if it crashes the compiler (in CL implementations where the compiler is promised to never respond to bad code by signaling an error.) This was also the approach jsfunfuzz took on Javascript. (3) Extensive fuzzing of calls to standard functions in CL, using random generation of input values and random generation of valid type declarations, with the invariant being that the same values should be computed (and the compiler not fail.) This is a specialization of (1), but was sufficiently different that the bugs it found were not the same. Examples of tests produced by (1) and (3) over an early period when this was being developed. Each caused a failure in some CL implementation: https://github.com/pfdietz/ansi-test/blob/master/misc/misc.l... This was one of my favorite bugs found: https://bugs.launchpad.net/sbcl/+bug/1730699 The experience with this sort of testing of compilers (in any language) is that if the compiler (free or commercial) has never been subjected to it, it will immediately find bugs in the compiler.