On 10/17/12 23:00, David Nadlinger wrote: > On Wednesday, 17 October 2012 at 20:37:53 UTC, Artur Skawina wrote: >> Well, I think such optimizations are fine (as long as documented and there >> exists alternatives), but note that this testcase checks for the case where >> the object size calculation overflows. Ie it must not succeed. > > Could you elaborate on that? It strikes me that this is either a GC > implementation detail or invalid D code in the first place (i.e. should not > be expected to compile resp. is undefined behavior).
Well, eg on a 32-bit platform the newly allocated memory object would need to have a size of 8*2G == 16G. I guess you could see it as a GC implementation detail, but that allocation can never succeed, simply because such an object would be larger than the available address space, hence can't be mapped directly. The 'new long[ptrdiff_t.max]' case can be caught at compile time, but a different 'new long[runtime_variable_which_happens_to_be_2G]' can not, and then the GC MUST catch the overflow, instead of allocating a ((size_t)long.sizeof*2G) sized object Which is what I assume that test was meant to check. But even in the constant, statically-checkable case, would it make sense to ignore the error if the allocation was "dead"? If nothing ever accesses the new object, ignoring the error seems harmless. But is it OK to allow faulty code to silently run long as the compiler can prove that the bug won't be triggered? Will every compiler make the same decision? Would a different optimization level cause the error to be thrown? For these reasons, silently optimizing away "harmless", but buggy code is not a good idea. artur
