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...bug as https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fbugs.llvm.org%2Fshow_bug.cgi%3Fid%3D31652&data=02%7C01%7Cnlopes%40microsoft.com%7C971ae2063c8b420d2f1008d4cbec8f22%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C636357664258073352&sdata=iCy8kUlWwJzQpXbXvOuhHpKyXBnntZPGvn%2FtxWsqun8%3D&reserved=0. The short answer here is that the loop unswitch transform and the GVN transform are justified via conflicting specifications of undef (that is, LoopUnswitch and GVN don't agree on the definition of undef). The long(er) answer is in the bug. Unfortunately, there is no real w...

...> protection.outlook.com/?url=https%3A%2F%2Fbugs.llvm.org% > 2Fshow_bug.cgi%3Fid%3D31652&data=02%7C01%7Cnlopes%40microsoft.com% > 7C971ae2063c8b420d2f1008d4cbec8f22%7C72f988bf86f141af91ab2d7cd011 > db47%7C1%7C0%7C636357664258073352&sdata=iCy8kUlWwJzQpXbXvOuhHpKyXBnntZ > PGvn%2FtxWsqun8%3D&reserved=0. > > The short answer here is that the loop unswitch transform and the GVN > transform are justified via conflicting specifications of undef (that is, > LoopUnswitch and GVN don't agree on the definition of undef). The > > long(er) answer is in the bug. >...

This is a bug found by internal compiler bootstrap, and possibly it is the root cause of https://bugs.llvm.org/show_bug.cgi?id=33652 and https://bugs.llvm.org/show_bug.cgi?id=33626. Here is the testcase 1.c. The original code is at MemorySSA.cpp:586 for rL307764. ------------------------- 1.c --------------------------- long a, c, d, e, f, m, cnt, i_hasval; volatile long b; void goo(long); void