The problematic scenario is that a function receives an @in_guaranteed and @inout parameter where one is a copy of the other value. For example, when appending a container to itself.
In this case the optimization removed the copy_addr, resulting in passing the same stack location to both parameters.
rdar://problem/47632890
This is a separate optimization that detects short-lived temporaries that can be eliminated.
This is necessary now that SILGen no longer performs basic RValue forwarding in some cases.
SR-5508: Performance regression in benchmarks caused by removing SILGen peephole for LoadExpr in +0 context
