[CodeGen] Build the core MachineIR object model

Add arena-owned, address-stable MachineFunction, MachineBasicBlock, and MachineInstr nodes with intrusive layout and instruction lists. Model every required MachineOperand category, reciprocal ties, source state, and immutable per-instruction memory references.

Implement physical and virtual register def-use chains whose back-links survive operand vector moves, plus vreg properties, tombstones, live-ins, reserved registers, and atomic CFG updates. Exercise ownership, reallocation, unlink/relink, cross-function rejection, and sanitizer paths.

1 files changed, 39 insertions, 0 deletions

diff --git a/backend/include/rcc/CodeGen/MachineCFGUpdater.h b/backend/include/rcc/CodeGen/MachineCFGUpdater.h
new file mode 100644
index 0000000..4359538
--- /dev/null
+++ b/backend/include/rcc/CodeGen/MachineCFGUpdater.h
@@ -0,0 +1,39 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+#ifndef RCC_CODEGEN_MACHINECFGUPDATER_H
+#define RCC_CODEGEN_MACHINECFGUPDATER_H
+
+#include "rcc/CodeGen/MachineIRTypes.h"
+#include "rcc/Support/Error.h"
+
+namespace rcc {
+
+class MachineBasicBlock;
+class MachineFunction;
+
+class MachineCFGUpdater final {
+public:
+  explicit MachineCFGUpdater(MachineFunction &Function) noexcept : Function(&Function) {}
+
+  [[nodiscard]] Expected<void>
+  addSuccessor(MachineBasicBlock &From, MachineBasicBlock &To,
+               BranchProbability Probability = BranchProbability::zero());
+  [[nodiscard]] Expected<void> removeSuccessor(MachineBasicBlock &From, MachineBasicBlock &To);
+  [[nodiscard]] Expected<void> replaceSuccessor(MachineBasicBlock &From,
+                                                MachineBasicBlock &OldTarget,
+                                                MachineBasicBlock &NewTarget);
+  [[nodiscard]] Expected<void> updateBranchProbability(MachineBasicBlock &From,
+                                                       MachineBasicBlock &To,
+                                                       BranchProbability Probability);
+  [[nodiscard]] Expected<void> transferSuccessors(MachineBasicBlock &From, MachineBasicBlock &To);
+  [[nodiscard]] Expected<void> disconnectBlock(MachineBasicBlock &Block);
+
+private:
+  [[nodiscard]] Expected<void> verifyOwnership(const MachineBasicBlock &Block) const;
+
+  MachineFunction *Function;
+};
+
+} // namespace rcc
+
+#endif // RCC_CODEGEN_MACHINECFGUPDATER_H