4 files changed, 29 insertions, 14 deletions

diff --git a/llvm/include/llvm/Target/TargetRegisterInfo.h b/llvm/include/llvm/Target/TargetRegisterInfo.h
index 1c5d7c71187..d06cdc4e8e5 100644
--- a/llvm/include/llvm/Target/TargetRegisterInfo.h
+++ b/llvm/include/llvm/Target/TargetRegisterInfo.h
@@ -588,11 +588,13 @@ public:
   }
 
   /// getCrossCopyRegClass - Returns a legal register class to copy a register
-  /// in the specified class to or from. Returns NULL if it is possible to copy
-  /// between a two registers of the specified class.
+  /// in the specified class to or from. If it is possible to copy the register
+  /// directly without using a cross register class copy, return the specified
+  /// RC. Returns NULL if it is not possible to copy between a two registers of
+  /// the specified class.
   virtual const TargetRegisterClass *
   getCrossCopyRegClass(const TargetRegisterClass *RC) const {
-    return NULL;
+    return RC;
   }
 
   /// getRegPressureLimit - Return the register pressure "high water mark" for
diff --git a/llvm/lib/CodeGen/SelectionDAG/ScheduleDAGFast.cpp b/llvm/lib/CodeGen/SelectionDAG/ScheduleDAGFast.cpp
index e3da2084529..7b560d173ed 100644
--- a/llvm/lib/CodeGen/SelectionDAG/ScheduleDAGFast.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/ScheduleDAGFast.cpp
@@ -570,13 +570,20 @@ void ScheduleDAGFast::ListScheduleBottomUp() {
           TRI->getMinimalPhysRegClass(Reg, VT);
         const TargetRegisterClass *DestRC = TRI->getCrossCopyRegClass(RC);
 
-        // If cross copy register class is null, then it must be possible copy
-        // the value directly. Do not try duplicate the def.
+        // If cross copy register class is the same as RC, then it must be
+        // possible copy the value directly. Do not try duplicate the def.
+        // If cross copy register class is not the same as RC, then it's
+        // possible to copy the value but it require cross register class copies
+        // and it is expensive.
+        // If cross copy register class is null, then it's not possible to copy
+        // the value at all.
         SUnit *NewDef = 0;
-        if (DestRC)
+        if (DestRC != RC) {
           NewDef = CopyAndMoveSuccessors(LRDef);
-        else
-          DestRC = RC;
+          if (!DestRC && !NewDef)
+            report_fatal_error("Can't handle live physical "
+                               "register dependency!");
+        }
         if (!NewDef) {
           // Issue copies, these can be expensive cross register class copies.
           SmallVector<SUnit*, 2> Copies;
diff --git a/llvm/lib/CodeGen/SelectionDAG/ScheduleDAGRRList.cpp b/llvm/lib/CodeGen/SelectionDAG/ScheduleDAGRRList.cpp
index f1a5a6599b2..5e60aa04eae 100644
--- a/llvm/lib/CodeGen/SelectionDAG/ScheduleDAGRRList.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/ScheduleDAGRRList.cpp
@@ -1140,13 +1140,19 @@ SUnit *ScheduleDAGRRList::PickNodeToScheduleBottomUp() {
       TRI->getMinimalPhysRegClass(Reg, VT);
     const TargetRegisterClass *DestRC = TRI->getCrossCopyRegClass(RC);
 
-    // If cross copy register class is null, then it must be possible copy
-    // the value directly. Do not try duplicate the def.
+    // If cross copy register class is the same as RC, then it must be possible
+    // copy the value directly. Do not try duplicate the def.
+    // If cross copy register class is not the same as RC, then it's possible to
+    // copy the value but it require cross register class copies and it is
+    // expensive.
+    // If cross copy register class is null, then it's not possible to copy
+    // the value at all.
     SUnit *NewDef = 0;
-    if (DestRC)
+    if (DestRC != RC) {
       NewDef = CopyAndMoveSuccessors(LRDef);
-    else
-      DestRC = RC;
+      if (!DestRC && !NewDef)
+        report_fatal_error("Can't handle live physical register dependency!");
+    }
     if (!NewDef) {
       // Issue copies, these can be expensive cross register class copies.
       SmallVector<SUnit*, 2> Copies;
diff --git a/llvm/lib/Target/X86/X86RegisterInfo.cpp b/llvm/lib/Target/X86/X86RegisterInfo.cpp
index fe98cacb836..1f464f4be43 100644
--- a/llvm/lib/Target/X86/X86RegisterInfo.cpp
+++ b/llvm/lib/Target/X86/X86RegisterInfo.cpp
@@ -337,7 +337,7 @@ X86RegisterInfo::getCrossCopyRegClass(const TargetRegisterClass *RC) const {
     else
       return &X86::GR32RegClass;
   }
-  return NULL;
+  return RC;
 }
 
 unsigned