llvm

llvm has a very thorough test suite and it's main test suite is exactly for this purpose. The error witnessed here by sqlite will be turned into a test case that takes the C code and compiles it and hand checks whether the output was miscompiled or not. Here's a test from 2007 that tests a similar error in the instruction selector: https://github.com/llvm-project/llvm/blob/master/test/CodeGe... Evidently the error that caused this test to be rewritten reordered the `ret` instruction before the `mov $1, $eax` instruction that sets the return value. This tests assures that the bug will never happen again.

An example of Instructions being implemented in Microcode is AMD's implementation of PDEP and PEXT on the Zen and Zen2 chips, leading to shockingly bad performance of 289 cycles vs 1 on Intel: https://twitter.com/uops_info/status/1202950247900684290 https://github.com/llvm-project/llvm/blob/master/lib/Target/...