Unlike GCC, clang will iterate gvn (what GCC calls fre, because in GCC, gvn is properly split into an analysis, and fre uses it to do full redundancy eliminatio

Unlike GCC, clang will iterate gvn (what GCC calls fre, because in GCC, gvn is properly split into an analysis, and fre uses it to do full redundancy elimination) until it stops changing, and does so fairly early in the pipeline I wrote fre for GCC (and working on llvm's next gvn) and long story short, GCC is more powerful, but it doesn't always run early enough, and is not iterated. The general problem of detecting all herbrand equivalences is exponential time, even without trying to evaluate the code. So you can't win all the time anyway.