This is a follow-up to https://github.com/llvm/llvm-project/pull/130210.
The EphemeralValuesAnalysis pass used to return an EphemeralValuesCache
object which used to hold the ephemeral values and used to provide a
lazy collection of the ephemeral values, and an invalidation using the
`clear()` function.
This patch removes the EphemeralValuesCache class completely and instead
returns the SmallVector containing the ephemeral values.
This patch does two things:
1. It implements an ephemeral values cache analysis pass that collects the ephemeral values of a function and caches them for fast lookups. The collection of the ephemeral values is done lazily when the user calls `EphemeralValuesCache::ephValues()`.
2. It adds caching of ephemeral values using the `EphemeralValuesCache` to speed up `CallAnalyzer::analyze()`. Without caching this can take a long time to run in cases where the function contains a large number of `@llvm.assume()` calls and a large number of callsites. The time is spent in `collectEphemeralvalues()`.
