Yes, the same thought occurred to me (that perhaps clang is careful in the caller in the case the address escapes), but I seemed to find cases where clang optim

Yes, the same thought occurred to me (that perhaps clang is careful in the caller in the case the address escapes), but I seemed to find cases where clang optimizes the caller also, so that two distinct objects receive the same pointer and both pointers escape. Here's an example: https://godbolt.org/g/yxFzqT https://godbolt.org/g/yxFzqT This happens on clang versions back 3.6. Note that if you change the caller to: Foo f; f = callee(&f); the code changes and distinct objects are passed. I'm not sure if the first form (all in the definition) has a relevant difference per the standard that lets clang do this.