Summary:
This optimisation will allow GCC to access more than one object from
the same symbolic address. For example, suppose a section contains
two variables x and y, and x and y are close together. The
optimisation will create a common anchor point -- let's call it A --
and allow both x and y to be accessed from A.
The optimisation will of course be subject to the usual binding
rules and will need to be aware of special cases like mergeable
constants.
At the moment, GCC makes no assumptions about the relative positions
of static variables and constants, writing them out in a
more-or-less arbitrary order. A major part of the project will
therefore be to assign specific positions to objects and to write
them out appropriately.
The new infrastructure will also allow GCC to reorder objects within
a section. Such a reordering might try to reduce the number of
anchors or improve cache locality. However, this aspect of the
project will be open-ended and isn't going to be part of the initial
patch.
Full details here:
http://gcc.gnu.org/wiki/Section%20Anchor%20Optimisations
Richard
