GC: fix wrong profile result if more than 4GB used

[rainers]

No description provided.

[dlang-bot]

Thanks for your pull request, @rainers!

Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	19847	minor	no GC memory above 4GB reported with --DRT-gcopt=profile:1

Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub fetch digger
dub run digger -- build "stable + druntime#2599"

[thewilsonator]

Does this have a bugzilla? Also this is so trivial it should go to stable.

[rainers]

Added bug report and rebased to stable. A test case is a bit problematic because allocating more than 4GB might be a problem on some CI machines.

[thewilsonator]

Thanks!

[jacob-carlborg]

Is it possible to make an artificial test, by somehow manually setting mappedPages to a big value?

[rainers]

Is it possible to make an artificial test, by somehow manually setting mappedPages to a big value?

Possible, but I think that would be rather invasive for such a trivial fix. It would be nice if the compiler would warn about cases like these, i.e. when the result of a calculation might overflow an int, but the assigned lvalue has larger size (similar for comparisons).

[PetarKirov]

I wonder if it would be better to instead change the type of the PAGESIZE enum to size_t. That way any arithmetic operation where one of the operands is PAGESIZE would promote the other operand as necessary.