jkotas on GCTables
-Werrorfor now, too many unused variables around. At the moment I will focus on small patches blocking build -- so one more patch to go to get it buildable and I will follow up with elimination of warnings.
Quoting coreclr#4331 (comment):
As far as an LLVM based upper tier goes -- obviously we have looked into this to some extent with LLILC, and at the time we were in frequent contact with the Azul folks, so we are familiar with many of the things they were doing in LLVM to make it more amenable to compilation of languages with precise GC.
There were (and likely still are) significant differences in the LLVM support needed for the CLR versus what is needed for Java, both in GC and in EH, and in the restrictions one must place on the optimizer. To cite just one example: the CLRs GC currently cannot tolerate managed pointers that point off the end of objects. Java handles this via a base/derived paired reporting mechanism. We'd either need to plumb support for this kind of paired reporting into the CLR or restrict LLVM's optimizer passes to never create these kinds of pointers. On top of that, the LLILC jit was slow and we weren't sure ultimately what kind of code quality it might produce.
So, figuring out how LLILC might fit into a potential multi-tier approach that did not yet exist seemed (and still seems) premature. The idea for now is to get tiering into the framework and use RyuJit for the second-tier jit. As we learn more, we may discover there is indeed room for higher tier jits, or, at least, understand better what else we need to do before such things make sense.