[llvm] [RISCV] Use TableGen-based macro fusion (PR #72224)

[Wang Pengcheng via llvm-commits]

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@@ -200,6 +200,7 @@ def SiFive7Model : SchedMachineModel {
                              HasStdExtZcmt, HasStdExtZknd, HasStdExtZkne,
                              HasStdExtZknh, HasStdExtZksed, HasStdExtZksh,
                              HasStdExtZkr];
+  let MacroFusions = [LUIADDI];
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wangpc-pp wrote:

Good question! I was thinking about testability too since we can't provide subtarget feature in `-mattr` anymore. Do you have any suggestion?

https://github.com/llvm/llvm-project/pull/72224