This is obviously a hard line to draw.
I tend to draw it at "research produces new things that were not previously known, engineering may produce new insights or improvements of things that were already known".
(but again, I admit this is not a very very bright line)
I consider graal to be good engineering.
It is a new arrangement and engineering of existing techniques.
That will in fact, often produce new papers.
For example, I built the first well-engineered value based partial redundancy elimination in GCC. before that, there were zero production implementations, and it was considered "too slow to be productionizable" until i took a whack at it. I helped with some papers on it.
It's not research, just good engineering. The theory was known, etc. I just made it practical. That wasn't research.
Another example: LLVM now has the first shipping implementation ever of an efficient incremental dominator tree updating scheme (that i'm aware of. GCC has a scheme to do it for some things, but it's not efficient). Again, previously not efficient.
Theory has been published.
Again, making it work well is just good engineering.
Another example: LLVM's phi placement algorithm is a linear time algorithm based on sreedhar and gao's work. If you read further research papers, they actually pretty much crap on this algorithm as very inefficient.
It turns out they were just bad at implementing it effectively, and LLVM's version is way faster than anything else out there. Is it research because our results are orders of magnitude better than anything else out there?
No. It may be cool, it may be amazing, etc, but it's still engineering.
Remember that conferences like PLDI and CGO accept papers not just on research, but on implementation engineering.
All that said, i also don't consider trying to differentiate heavily between research and engineering to be that horribly interesting (though i know some prize one or the other).