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Recent versions of GCC turn on the option -fstrict-aliasing (which allows alias-based optimizations) by default with -O2. Some architectures then print "1111 1111" as a result. Without optimization, the executable will generate generates the "expected" output "2222 2222".
To disable optimizations based on alias-analysis for faulty legacy code, the option -fno-strict-aliasing can be used as a workaround. The option -Wstrict-aliasing (which is included in -Wall) warns about some, but not all, violations of aliasing rules when -fstrict-aliasing is active.
When GCC 3.4.6 compiles this code with optimization, the assignment through the aliased pointer is effectively eliminated.
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