Jacques Pienaar, a software engineer at Google since 2014, posted patches today seeking to mainline a "Lanai" back-end inside LLVM. He explained they want to contribute their Lanai processor to the LLVM code-base as they continue developing this back-end with a focus on compiling C99 code. He mentions Lanai is a simple in-order 32-bit processor with 32 x 32-bit registers, two registers with fixed values, four used for program state tracking, and two reserved for explicit usage by user, and no floating point support.
A footnote to the patches confirm the Lanai processor is derived from the data presented by this book: Parallel Computer Architecture: A Hardware/Software Approach originally published in 1997.
When asked about this "Lanai" processor back-end for LLVM, Chandler Carruth, a compiler expert at Google known for his open-source contributions, commented: "This is internal hardware for us, so there's not a lot we can share, and you can't really grab a version of the hardware."
Rumors have been swirling for months (and years) that Google has been pursing their own processors, but at least for Lanai it looks like a CPU used just internally and isn't something that is going to power the next generation of Android devices; the public details from the patch series about Lanai aren't anything special. Lanai seems to be a network/communications processor with some references to it being as LANai. From other searches about Lanai, it appears the processor may be manufactured by Myricom.
If any other details about Google's Lanai emerge, I'll certainly pass it along. The Lanai usage at Google appears relatively new as they are still developing this LLVM processor back-end, planning more optimizations for it, etc.