On 7/2/2017 5:46 AM, Shachar Shemesh wrote:
Second, there are optimizations that can take place over "const" that cannot
over "shared const" even assuming aliasing (such as if the compiler knows no
other pointer was changed between two accesses).
The last point is that assuming no pointer aliasing is a fairly common
optimization to take in C and C++, simply because of the huge performance gains
it provides. It is so huge that it is sometimes turned on by default despite the
fact it changes language semantics. It would be a pity to block any potential to
have it in D.
Pointer aliasing is indeed a big deal for optimization.
But that really has nothing to do with const in C++. The trouble with C++ const
is you can legally cast it away in C++. Chandler Carruth (LLVM optimizer) told
me that const was basically ignored by the optimizer because of that.
D const is different in that the compiler is allowed to generate code as if
const was never cast to immutable. Such casts are also not allowed in @safe code.
