Hi Richard and Jonathan
On 18/09/2023 10:00, Richard Biener wrote:
On Mon, Sep 18, 2023 at 9:24 AM Jonathan Wakely via Gcc<gcc@gcc.gnu.org> wrote:
Yes, GCC assumes that the reference is bound to a valid object, because C++
requires that to be true. Of course memcheck can't assume that, because one
of its main reasons to exist is to find undefined behaviour where that
isn't true!
It's even worse than that. This transformation is being done in VEX
(which unfortunately
is also the bit I know the least). Not normally where we'd do
accessibility checks.
I think what GCC is doing is a valid transformation, in the context of a
valid C++ program. But I'm not sure that helps valgrind, which doesn't have
the liberty of assuming a valid program.
More specifically GCC thinks it's fine to speculate loads (given it can prove
doing so doesn't trap)
I don't think that will be easy for us to prove. We just don't know
enough about stack variables.
A+
Paui
