And C compilers routinely optimize structures in such a way that they are impossible to inspect in a debugger. Because of SRA, non escaping aggregates might even not be allocated on a memory location at all.
What is an "escaping aggregate"?; this term has 80 hits on Google, none of which seem to be related to programming.
Looking it up “aggregate” is a C++ term for which the standard indeed does explicitly allow various optimizations and guarantees about data layout are weakened; this is not the case with C arrays.
Do you have any practical evidence to C compilers altering the data layout of an array in any way?
GP’s comment is referring to Scalar Replacement of Aggregates on the one hand. This is an optimization where by the compiler will, for a function with a Struct argument, only pass in a pointer to / copy of the actual element of the struct used inside a function. Hence the name, the compiler is replacing the aggregate struct by one or more of the individual values it contains.
The reference to non-escaping aggregates, describes the compiler optimizing a local only struct by keeping the individual elements in registers during usage, and because the struct as a whole does not leave the local scope, these elements are just discarded when that scope closes.
Both of these transformations/optimizations are performed by all three industrial C and C++ compilers (gcc/llvm/msvc).
