[llvm] [AArch64][MacroFusion] Fuse only tied AES pairs post-RA (PR #201610)

[David Green via llvm-commits]

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@@ -117,6 +117,18 @@ static bool isArithmeticCbzPair(const MachineInstr *FirstMI,
   return false;
 }
 
+// True unless the pair provably writes different physical registers. Pre-RA
+// the dests are still virtual, and post-RA it requires a genuine WAW (same dest
+// reg).
+static bool mayHaveWAWDependency(const MachineInstr &FirstMI,
+                                 const MachineInstr &SecondMI) {
+  Register DestFirst = FirstMI.getOperand(0).getReg();
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davemgreen wrote:

Can return true for SecondMI.getOpcode() == AArch64::AESMCrrTied to avoid the need to look at the registers.

https://github.com/llvm/llvm-project/pull/201610