[llvm] [GISel] Explicitly disable BF16 tablegen patterns. (PR #124113)

[David Green via llvm-commits]

davemgreen wrote:

Thanks for the heads up - it looks like after we fall back from global-isel to SDAG, the verifier gets called, which calls getReservedRegs which uses SIMachineFunctionInfo::usesAGPRs which caches the result of UsesAGPRs. Because we have just fallen-back the function is empty and it incorrectly gets cached to false. This then causes a regallocation failure. One way around it might be to make sure we do not call getReservedRegs on an empty function in the verifier, but it may be better to reset that cached value somewhere, I'm just not sure where.

https://github.com/llvm/llvm-project/pull/124113