[llvm] [ConstraintElim] Use constraints from bounded memory accesses (PR #155253)

[Sam Elliott via llvm-commits]

lenary wrote:

Sorry for coming back to this so long after the fact. Hopefully this comment helps others.

We started seeing new failures in some of our downstream testing after this patch. In both cases, these were in tests we had not yet added `-fno-strict-overflow` (or equivalents) to.

The tests were:
- `spec2006/h264ref`, which has an out-of-bounds access in the `SATD` function when `use_hadamard` is true - the load of elements from `d` is done before the index is checked against the length (the access is only used if the check succeeds).
- `eembc/telecom_suite` - in the `viterb00` tests, in the `t_run_test` function, the `T_OUTPUT` expression which is used for the size of the allocation for the output result is incorrectly associated, which means it does not allocate enough space for the later comparison of the results with the golden model.

Both issues can be solved with `-fno-strict-overflow`. This patch does not need updating.

https://github.com/llvm/llvm-project/pull/155253