2 files changed, 43 insertions, 3 deletions

diff --git a/include/llvm/CodeGen/RegisterClassInfo.h b/include/llvm/CodeGen/RegisterClassInfo.h
index 12bd1c61d2..3ad22e65c8 100644
--- a/include/llvm/CodeGen/RegisterClassInfo.h
+++ b/include/llvm/CodeGen/RegisterClassInfo.h
@@ -29,9 +29,14 @@ class RegisterClassInfo {
     unsigned Tag;
     unsigned NumRegs;
     bool ProperSubClass;
+    uint8_t MinCost;
+    uint16_t LastCostChange;
     OwningArrayPtr<MCPhysReg> Order;
 
-    RCInfo() : Tag(0), NumRegs(0), ProperSubClass(false) {}
+    RCInfo()
+      : Tag(0), NumRegs(0), ProperSubClass(false), MinCost(0),
+        LastCostChange(0) {}
+
     operator ArrayRef<MCPhysReg>() const {
       return makeArrayRef(Order.get(), NumRegs);
     }
@@ -106,6 +111,21 @@ public:
       return CalleeSaved[N-1];
     return 0;
   }
+
+  /// Get the minimum register cost in RC's allocation order.
+  /// This is the smallest value returned by TRI->getCostPerUse(Reg) for all
+  /// the registers in getOrder(RC).
+  unsigned getMinCost(const TargetRegisterClass *RC) {
+    return get(RC).MinCost;
+  }
+
+  /// Get the position of the last cost change in getOrder(RC).
+  ///
+  /// All registers in getOrder(RC).slice(getLastCostChange(RC)) will have the
+  /// same cost according to TRI->getCostPerUse().
+  unsigned getLastCostChange(const TargetRegisterClass *RC) {
+    return get(RC).LastCostChange;
+  }
 };
 } // end namespace llvm
 
diff --git a/lib/CodeGen/RegisterClassInfo.cpp b/lib/CodeGen/RegisterClassInfo.cpp
index 078a0df915..87382d8f7c 100644
--- a/lib/CodeGen/RegisterClassInfo.cpp
+++ b/lib/CodeGen/RegisterClassInfo.cpp
@@ -83,6 +83,9 @@ void RegisterClassInfo::compute(const TargetRegisterClass *RC) const {
 
   unsigned N = 0;
   SmallVector<MCPhysReg, 16> CSRAlias;
+  unsigned MinCost = 0xff;
+  unsigned LastCost = ~0u;
+  unsigned LastCostChange = 0;
 
   // FIXME: Once targets reserve registers instead of removing them from the
   // allocation order, we can simply use begin/end here.
@@ -92,17 +95,31 @@ void RegisterClassInfo::compute(const TargetRegisterClass *RC) const {
     // Remove reserved registers from the allocation order.
     if (Reserved.test(PhysReg))
       continue;
+    unsigned Cost = TRI->getCostPerUse(PhysReg);
+    MinCost = std::min(MinCost, Cost);
+
     if (CSRNum[PhysReg])
       // PhysReg aliases a CSR, save it for later.
       CSRAlias.push_back(PhysReg);
-    else
+    else {
+      if (Cost != LastCost)
+        LastCostChange = N;
       RCI.Order[N++] = PhysReg;
+      LastCost = Cost;
+    }
   }
   RCI.NumRegs = N + CSRAlias.size();
   assert (RCI.NumRegs <= NumRegs && "Allocation order larger than regclass");
 
   // CSR aliases go after the volatile registers, preserve the target's order.
-  std::copy(CSRAlias.begin(), CSRAlias.end(), &RCI.Order[N]);
+  for (unsigned i = 0, e = CSRAlias.size(); i != e; ++i) {
+    unsigned PhysReg = CSRAlias[i];
+    unsigned Cost = TRI->getCostPerUse(PhysReg);
+    if (Cost != LastCost)
+      LastCostChange = N;
+    RCI.Order[N++] = PhysReg;
+    LastCost = Cost;
+  }
 
   // Register allocator stress test.  Clip register class to N registers.
   if (StressRA && RCI.NumRegs > StressRA)
@@ -113,6 +130,9 @@ void RegisterClassInfo::compute(const TargetRegisterClass *RC) const {
     if (Super != RC && getNumAllocatableRegs(Super) > RCI.NumRegs)
       RCI.ProperSubClass = true;
 
+  RCI.MinCost = uint8_t(MinCost);
+  RCI.LastCostChange = LastCostChange;
+
   DEBUG({
     dbgs() << "AllocationOrder(" << RC->getName() << ") = [";
     for (unsigned I = 0; I != RCI.NumRegs; ++I)