[llvm] [MacroFusion][RISCV] Allocate same register for second instruction of fusible pair (PR #77461)

[Mikhail Gudim via llvm-commits]

================
@@ -114,6 +114,7 @@ class MachineInstr
                              // this instruction.
     Unpredictable = 1 << 16, // Instruction with unpredictable condition.
     NoConvergent = 1 << 17,  // Call does not require convergence guarantees.
+    Fusible = 1 << 18,       // Instruction is the second of a fusible pair.
----------------
mgudim wrote:

Is the point to add a flag to simplify the code which detects fusible patterns? I realise that some processors may have a lot of fusions, but is adding a new flag really the right solution?

https://github.com/llvm/llvm-project/pull/77461