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

1 files changed, 68 insertions, 0 deletions

diff --git a/lib/CodeGen/AllocationOrder.cpp b/lib/CodeGen/AllocationOrder.cpp
new file mode 100644
index 0000000000..3f08439fac
--- /dev/null
+++ b/lib/CodeGen/AllocationOrder.cpp
@@ -0,0 +1,68 @@
+//===-- llvm/CodeGen/AllocationOrder.cpp - Allocation Order ---------------===//
+//
+//                     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.
+//
+//===----------------------------------------------------------------------===//
+
+#include "AllocationOrder.h"
+#include "VirtRegMap.h"
+#include "llvm/CodeGen/MachineRegisterInfo.h"
+
+using namespace llvm;
+
+// Compare VirtRegMap::getRegAllocPref().
+AllocationOrder::AllocationOrder(unsigned VirtReg,
+                                 const VirtRegMap &VRM,
+                                 const BitVector &ReservedRegs)
+  : Pos(0), Reserved(ReservedRegs) {
+  const TargetRegisterClass *RC = VRM.getRegInfo().getRegClass(VirtReg);
+  std::pair<unsigned, unsigned> HintPair =
+    VRM.getRegInfo().getRegAllocationHint(VirtReg);
+
+  // HintPair.second is a register, phys or virt.
+  Hint = HintPair.second;
+
+  // Translate to physreg, or 0 if not assigned yet.
+  if (Hint && TargetRegisterInfo::isVirtualRegister(Hint))
+    Hint = VRM.getPhys(Hint);
+
+  // Target-dependent hints require resolution.
+  if (HintPair.first)
+    Hint = VRM.getTargetRegInfo().ResolveRegAllocHint(HintPair.first, Hint,
+                                                      VRM.getMachineFunction());
+
+  // The hint must be a valid physreg for allocation.
+  if (Hint && (!TargetRegisterInfo::isPhysicalRegister(Hint) ||
+               !RC->contains(Hint) || ReservedRegs.test(Hint)))
+    Hint = 0;
+
+  // The remaining allocation order may also depend on the hint.
+  tie(Begin, End) = VRM.getTargetRegInfo()
+        .getAllocationOrder(RC, HintPair.first, Hint, VRM.getMachineFunction());
+}
+
+unsigned AllocationOrder::next() {
+  // First take the hint.
+  if (!Pos) {
+    Pos = Begin;
+    if (Hint)
+      return Hint;
+  }
+  // Then look at the order from TRI.
+  while(Pos != End) {
+    unsigned Reg = *Pos++;
+    if (Reg != Hint && !Reserved.test(Reg))
+      return Reg;
+  }
+  return 0;
+}