Currently, C2 can only elide pre-and post-barriers of G1 stores that follow immediately a newly allocated object. This RFE proposes analyzing C2's IR platform-dependent representation right before code emission (at PhaseOutput::perform_mach_node_analysis()) to elide barriers in stores as long as there is no safepoint poll between these and their corresponding allocations. Existing ZGC logic to perform a similar analysis can hopefully by generalized and reused.

The additional optimization would make it possible to remove barriers e.g. in conditional stores:

MyObject o = new MyObject();
if (c) {
    o.myField = ..; // elidable barrier
}

or in array initialization stores in small loops such as this:

Object[] a = new Object[64];
for (int i = 0; i < a.length; i++) {
    a[i] = ..; // elidable barrier (small counted loop without safepoint polls)
}