Re-commit 127368 and 127371. They are exonerated.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@127380 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 12 insertions, 5 deletions

diff --git a/lib/CodeGen/SelectionDAG/ScheduleDAGFast.cpp b/lib/CodeGen/SelectionDAG/ScheduleDAGFast.cpp
index e3da208452..7b560d173e 100644
--- a/lib/CodeGen/SelectionDAG/ScheduleDAGFast.cpp
+++ b/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;