[PATCH] [tablegen] Add !listconcat operator with the similar semantics as !strconcat

[Daniel Sanders]

I'm sorry to ping this patch again so soon but it's a bottleneck for a patch-series that adds assembler-only implementations of MIPS-I, MIPS-II, MIPS-III, and MIPS-V which has become quite important. It has become important because the it is itself a bottleneck for the minimal, functionally correct MIPS64r6 compiler we are urgently working on (we currently aim to get minimal MIPS64r6 support upstream by the end of the month). I could potentially re-work the dependent patch-series to override Instruction.Predicates instead of sublists that are concatenated to form the full predicates list but this is rather bug prone (while implementing MIPS-I to MIPS-V I found several cases of accidentally removing HasStdEnc with a 'let Predicates = ...' statement) and will require a significant amount of time.

Could someone review this patch which adds a !listconcat operator?

http://reviews.llvm.org/D3506