* Joe Buck: > It's wasted code if the multiply instruction detects the overflow. > It's true that the cost is small (maybe just one extra instruction > and the same number of tests, maybe one more on architectures where you > have to load a large constant), but it is slightly worse code than what > Chris Lattner showed.
It's possible to improve slightly on the LLVM code by using the overflow flag (at least on i386/amd64), as explained in this blog post: <http://blogs.msdn.com/b/michael_howard/archive/2005/12/06/500629.aspx> My patch emits a run-time division if a VLA is used in an allocator. But that's a semi-deprecated GCC extension, so I don't think we need to care. > Still, it's certainly an improvement on the current > situation and the cost is negligible compared to the call to the > allocator. Since it's a security issue, some form of the patch should > go in. Well, should I resubmit, with the fix for the problem building size_t(-1)?
