On Thu, 19 Apr 2018, Jakub Jelinek wrote:
As mentioned in the PR, this optimization can't work if @0's precision
is higher than @1's precision, because originally it compares just some set
of lower bits, but in the new comparison compares all bits.
If @0's precision is smaller than @1's precision (in this case @0 can't be
a pointer, as we disallow such direct casts), then in theory it can be
handled, but will not match what the comment says and we'd need to verify
that the @1 constant can be represented in the @0's precision.
This patch just verifies the precision is the same and does small formatting
cleanup. Bootstrapped/regtested on x86_64-linux and i686-linux, ok for
trunk?
That certainly seems safe, but I am surprised to see a direct cast from
64-bit pointer to 32-bit integer. I've always seen gcc represent those
with an intermediate cast to a 64-bit integer, even if
verify_gimple_assign_unary allows the direct cast. Does it depend on the
platform? It might be nice to canonicalize this a bit, either by
forbidding narrowing pointer-to-integer casts, or by simplifying cast
chains to direct casts.
--
Marc Glisse
