[llvm] [RISCV] Initial ISel support for the experimental zacas extension (PR #67918)

[Craig Topper via llvm-commits]

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@@ -728,6 +807,38 @@ bool RISCVExpandAtomicPseudo::expandAtomicCmpXchg(
   return true;
 }
 
+static Register getGPRPairEvenReg(Register PairedReg) {
+  assert(PairedReg >= RISCV::X0_PD && PairedReg <= RISCV::X30_PD &&
+         "Invalid GPR pair");
+  return (PairedReg - RISCV::X0_PD) * 2 + RISCV::X0;
+}
+
+bool RISCVExpandAtomicPseudo::expandAMOCAS(
+    MachineBasicBlock &MBB, MachineBasicBlock::iterator MBBI, bool IsPaired,
+    int Width, MachineBasicBlock::iterator &NextMBBI) {
+  MachineInstr &MI = *MBBI;
+  DebugLoc DL = MI.getDebugLoc();
+
+  Register DestReg = MI.getOperand(0).getReg();
+  if (IsPaired)
+    DestReg = getGPRPairEvenReg(DestReg);
+  Register AddrReg = MI.getOperand(1).getReg();
+  Register NewValReg = MI.getOperand(3).getReg();
+  if (IsPaired)
+    NewValReg = getGPRPairEvenReg(NewValReg);
+  AtomicOrdering Ordering =
+      static_cast<AtomicOrdering>(MI.getOperand(4).getImm());
+
+  MachineInstr *NewMI =
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topperc wrote:

Unused variable

https://github.com/llvm/llvm-project/pull/67918