Add an AllocationOrder class that can iterate over the allocatable physical

registers for a given virtual register.

Reserved registers are filtered from the allocation order, and any valid hint is
returned as the first suggestion.

For target dependent hints, a number of arcane target hooks are invoked.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@121497 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/AllocationOrder.h

@@ -0,0 +1,54 @@
+//===-- llvm/CodeGen/AllocationOrder.h - Allocation Order -*- C++ -*-------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements an allocation order for virtual registers.
+//
+// The preferred allocation order for a virtual register depends on allocation
+// hints and target hooks. The AllocationOrder class encapsulates all of that.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CODEGEN_ALLOCATIONORDER_H
+#define LLVM_CODEGEN_ALLOCATIONORDER_H
+
+namespace llvm {
+
+class BitVector;
+class VirtRegMap;
+
+class AllocationOrder {
+  const unsigned *Begin;
+  const unsigned *End;
+  const unsigned *Pos;
+  const BitVector &Reserved;
+  unsigned Hint;
+public:
+
+  /// AllocationOrder - Create a new AllocationOrder for VirtReg.
+  /// @param VirtReg      Virtual register to allocate for.
+  /// @param VRM          Virtual register map for function.
+  /// @param ReservedRegs Set of reserved registers as returned by
+  ///        TargetRegisterInfo::getReservedRegs().
+  AllocationOrder(unsigned VirtReg,
+                  const VirtRegMap &VRM,
+                  const BitVector &ReservedRegs);
+
+  /// next - Return the next physical register in the allocation order, or 0.
+  /// It is safe to call next again after it returned 0.
+  /// It will keep returning 0 until rewind() is called.
+  unsigned next();
+
+  /// rewind - Start over from the beginning.
+  void rewind() { Pos = 0; }
+
+};
+
+} // end namespace llvm
+
+#endif