> temp.a[dat[i]] = i; // This is what I'd meant
I see.
> struct blob temp1 = x; // Allowed initial value
With, I presume, a eye toward further producing:
x.a[dat[i]] = i;
y.a[dat[i]] = i;
?
> Compilers may replace an automatic object whose address is not observable with two objects,
That makes sense.
> do a sign-extending load from `x` and/or `y`
I assume you mean zero-extending; otherwise `x=255` would result in `result=-1`, which is clearly wrong.
> Should a compiler be required to initialize "result" in that situation, or should programmers be required to allow for the possibility that if they don't initialize an automatic object it might behave somewhat strangely?
Of course not. Result (assuming mode&3 == 0) is undefined, and behaviour characteristic of the environment is that result (aka eg eax) can hold any (say) 32-bit value (whether that's 0..FFFF'FFFF or -8000'0000..7FFF'FFFF depends on what operations are applied, but `int` suggests the latter).
None of this involves that the compiler infering objective (and frequently false) properties of the input program (such as "this loop will terminate" or "p != NULL"), though.
> Compilers may replace an automatic object whose address is not observable with two objects,
That makes sense.
> do a sign-extending load from `x` and/or `y`
I assume you mean zero-extending; otherwise `x=255` would result in `result=-1`, which is clearly wrong.
> Should a compiler be required to initialize "result" in that situation, or should programmers be required to allow for the possibility that if they don't initialize an automatic object it might behave somewhat strangely?
Of course not. Result (assuming mode&3 == 0) is undefined, and behaviour characteristic of the environment is that result (aka eg eax) can hold any (say) 32-bit value (whether that's 0..FFFF'FFFF or -8000'0000..7FFF'FFFF depends on what operations are applied, but `int` suggests the latter).
None of this involves that the compiler infering objective (and frequently false) properties of the input program (such as "this loop will terminate" or "p != NULL"), though.