Just to test this out, I created a 4.7G file of just '\n' and I see exactly the behavior described. I then tried a simple change (attached, based on 7.4.728) to have Vim use LONG_MAX for MAXLNUM rather than the hard-coded value. Now Vim didn't stop loading the file partway through, but it did get killed by the OOM killer after taking up 14G of RAM.
Just to test this out, I created a 4.7G file of just '\n' and I see exactly the behavior described. I then tried a simple change (attached, based on 7.4.728) to have Vim use LONG_MAX for MAXLNUM rather than the hard-coded value. Now Vim didn't stop loading the file partway through, but it did get killed by the OOM killer after taking up 14G of RAM.