Verify that debug info intrinsic arguments are valid. (These checks
will not recurse through the full debug info graph, so they don't need
to be cordoned of in `DebugInfoVerifier`.)
With those checks in place, changing the `DbgIntrinsicInst` accessors to
downcast to `MDLocalVariable` and `MDExpression` is natural (added isa
specializations in `Metadata.h` to support this).
Added tests to `test/Verifier` for the new -verify checks, and fixed the
debug info in all the in-tree tests.
If you have out-of-tree testcases that have started to fail to -verify,
hopefully the verify checks are helpful. The most likely problem is
that the expression argument is `!{}` (instead of `!MDExpression()`).
llvm-svn: 232296