https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117922
--- Comment #18 from Paolo Bonzini <bonzini at gnu dot org> --- > Can someone help me find what Paolo referenced as "the multiple definitions > DF problem > that was introduced for fwprop in 2009"? Yes, the patch is at https://gcc.gnu.org/pipermail/gcc-patches/2009-June/263754.html It's composed of two parts: 1) a cheap dataflow problem that records registers that have multiple definitions where the CFG joins. The problem instructs the pass to ignore completely those registers 2) a dominator walk to note use-def relations where there can be only one definition. The basic algorithm starts at function build_single_def_use_links() in fwprop.c. You can find the old version of the file in git, just ask if you have more questions.
