diff --git a/llvm/lib/CodeGen/SimpleRegisterCoalescing.cpp b/llvm/lib/CodeGen/SimpleRegisterCoalescing.cpp
index ce72b2fc1488..d25df1d2ad8c 100644
--- a/llvm/lib/CodeGen/SimpleRegisterCoalescing.cpp
+++ b/llvm/lib/CodeGen/SimpleRegisterCoalescing.cpp
@@ -1671,8 +1671,20 @@ bool SimpleRegisterCoalescing::JoinCopy(CopyRec &TheCopy, bool &Again) {
         // density, do not join them, instead mark the physical register as its
         // allocation preference.
         LiveInterval &JoinVInt = SrcIsPhys ? DstInt : SrcInt;
+        LiveInterval &JoinPInt = SrcIsPhys ? SrcInt : DstInt;
         unsigned JoinVReg = SrcIsPhys ? DstReg : SrcReg;
         unsigned JoinPReg = SrcIsPhys ? SrcReg : DstReg;
+
+        // Don't join with physregs that have a ridiculous number of live
+        // ranges. The data structure performance is really bad when that
+        // happens.
+        if (JoinPInt.ranges.size() > 1000) {
+          mri_->setRegAllocationHint(JoinVInt.reg, 0, JoinPReg);
+          ++numAborts;
+          DEBUG(dbgs() << "\tPhysical register too complicated, abort!\n");
+          return false;
+        }
+
         const TargetRegisterClass *RC = mri_->getRegClass(JoinVReg);
         unsigned Threshold = allocatableRCRegs_[RC].count() * 2;
         unsigned Length = li_->getApproximateInstructionCount(JoinVInt);