deep-recursion.c was disabled
(c007e0f66e)
because the test may get unlucky and end up with a zero-tagged variable,
leading to a false negative
(https://github.com/llvm/llvm-project/issues/69221).
This patch re-enables the test and adds a workaround: it checks
if the variable is zero-tagged, and if so, it will instead use the
neighboring variable, which must have a different (hence non-zero)
tag.
Fixing the stack allocation tagging is left as an exercise for the
reader. It is non-trivial because, even if the stackTagBase is
non-zero, tags for subsequent allocations in the stack frame may wrap
around to zero; working around this would require adding multiple
instructions to each alloca.
---------
Co-authored-by: Thurston Dang <thurston@google.com>
aa4dfd3736