Does initialization entail lvalue-to-rvalue conversion? Is `int x = x;` UB?

Question

The C++ standard contains a semi-famous example of \"surprising\" name lookup in 3.3.2, \"Point of declaration\":

int x = x;

This initializ

Answer 1

The behavior is not undefined. The variable is uninitialized and stays with whatever random value uninitialized values start up with. One example from clan'g test suit:

int test7b(int y) {
  int x = x; // expected-note{{variable 'x' is declared here}}
  if (y)
    x = 1;
  // Warn with "may be uninitialized" here (not "is sometimes uninitialized"),
  // since the self-initialization is intended to suppress a -Wuninitialized
  // warning.
  return x; // expected-warning{{variable 'x' may be uninitialized when used here}}
}

Which you can find in clang/test/Sema/uninit-variables.c tests for this case explicitly.