diff --git a/lib/CodeGen/SimpleRegisterCoalescing.cpp b/lib/CodeGen/SimpleRegisterCoalescing.cpp
index 7d9170a..249f4f4 100644
--- a/lib/CodeGen/SimpleRegisterCoalescing.cpp
+++ b/lib/CodeGen/SimpleRegisterCoalescing.cpp
@@ -616,19 +616,17 @@
     }
 
   MachineBasicBlock::iterator MII = next(MachineBasicBlock::iterator(CopyMI));
-  CopyMI->removeFromParent();
   tii_->reMaterialize(*MBB, MII, DstReg, DefMI);
   MachineInstr *NewMI = prior(MII);
 
   if (checkForDeadDef) {
-      // PR4090 fix: Trim interval failed because there was no use of the
-      // source interval in this MBB. If the def is in this MBB too then we
-      // should mark it dead:
-      if (DefMI->getParent() == MBB) {
-        DefMI->addRegisterDead(SrcInt.reg, tri_);
-        SrcLR->end = SrcLR->start + 1;
-      }
- 
+    // PR4090 fix: Trim interval failed because there was no use of the
+    // source interval in this MBB. If the def is in this MBB too then we
+    // should mark it dead:
+    if (DefMI->getParent() == MBB) {
+      DefMI->addRegisterDead(SrcInt.reg, tri_);
+      SrcLR->end = SrcLR->start + 1;
+    }
   }
 
   // CopyMI may have implicit operands, transfer them over to the newly
@@ -647,7 +645,7 @@
   }
 
   li_->ReplaceMachineInstrInMaps(CopyMI, NewMI);
-  MBB->getParent()->DeleteMachineInstr(CopyMI);
+  CopyMI->eraseFromParent();
   ReMatCopies.insert(CopyMI);
   ReMatDefs.insert(DefMI);
   ++NumReMats;
@@ -967,7 +965,7 @@
 
 /// RemoveCopiesFromValNo - The specified value# is defined by an implicit
 /// def and it is being removed. Turn all copies from this value# into
-/// identity copies so they will be removed.
+/// implicit_defs.
 void SimpleRegisterCoalescing::RemoveCopiesFromValNo(LiveInterval &li,
                                                      VNInfo *VNI) {
   SmallVector<MachineInstr*, 4> ImpDefs;
@@ -979,9 +977,8 @@
     MachineInstr *MI = &*RI;
     ++RI;
     if (MO->isDef()) {
-      if (MI->getOpcode() == TargetInstrInfo::IMPLICIT_DEF) {
+      if (MI->getOpcode() == TargetInstrInfo::IMPLICIT_DEF)
         ImpDefs.push_back(MI);
-      }
       continue;
     }
     if (JoinedCopies.count(MI))
@@ -994,13 +991,18 @@
     unsigned SrcReg, DstReg, SrcSubIdx, DstSubIdx;
     if (tii_->isMoveInstr(*MI, SrcReg, DstReg, SrcSubIdx, DstSubIdx) &&
         SrcReg == li.reg) {
-      // Each use MI may have multiple uses of this register. Change them all.
-      for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
-        MachineOperand &MO = MI->getOperand(i);
-        if (MO.isReg() && MO.getReg() == li.reg)
-          MO.setReg(DstReg);
-      }
-      JoinedCopies.insert(MI);
+      // Change it to an implicit_def.
+      MI->setDesc(tii_->get(TargetInstrInfo::IMPLICIT_DEF));
+      for (int i = MI->getNumOperands() - 1, e = 0; i > e; --i)
+        MI->RemoveOperand(i);
+      // It's no longer a copy, update the valno it defines.
+      unsigned DefIdx = li_->getDefIndex(UseIdx);
+      LiveInterval &DstInt = li_->getInterval(DstReg);
+      LiveInterval::iterator DLR = DstInt.FindLiveRangeContaining(DefIdx);
+      assert(DLR != DstInt.end() && "Live range not found!");
+      assert(DLR->valno->copy == MI);
+      DLR->valno->copy = NULL;
+      ReMatCopies.insert(MI);
     } else if (UseIdx > LastUseIdx) {
       LastUseIdx = UseIdx;
       LastUse = MO;
@@ -2641,6 +2643,11 @@
     return false;
   LiveInterval &DstInt = li_->getInterval(DstReg);
   const LiveRange *DstLR = DstInt.getLiveRangeContaining(CopyIdx);
+  // If the valno extends beyond this basic block, then it's not safe to delete
+  // the val# or else livein information won't be correct.
+  MachineBasicBlock *EndMBB = li_->getMBBFromIndex(DstLR->end);
+  if (EndMBB != MBB)
+    return false;
   DstInt.removeValNo(DstLR->valno);
   CopyMI->setDesc(tii_->get(TargetInstrInfo::IMPLICIT_DEF));
   for (int i = CopyMI->getNumOperands() - 1, e = 0; i > e; --i)
diff --git a/test/CodeGen/ARM/2009-06-15-RegScavengerAssert.ll b/test/CodeGen/ARM/2009-06-15-RegScavengerAssert.ll
new file mode 100644
index 0000000..c715a18
--- /dev/null
+++ b/test/CodeGen/ARM/2009-06-15-RegScavengerAssert.ll
@@ -0,0 +1,344 @@
+; RUN: llvm-as < %s | llc -mtriple=armv6-apple-darwin
+
+  %struct.term = type { i32, i32, i32 }
+
+declare fastcc i8* @memory_Malloc(i32) nounwind
+
+define fastcc %struct.term* @t1() nounwind {
+entry:
+	br i1 undef, label %bb, label %bb1
+
+bb:		; preds = %entry
+	ret %struct.term* undef
+
+bb1:		; preds = %entry
+	%0 = tail call fastcc i8* @memory_Malloc(i32 12) nounwind		; <i8*> [#uses=0]
+	%1 = tail call fastcc i8* @memory_Malloc(i32 12) nounwind		; <i8*> [#uses=0]
+	ret %struct.term* undef
+}
+
+
+define i32 @t2(i32 %argc, i8** nocapture %argv) nounwind {
+entry:
+	br label %bb6.i8
+
+bb6.i8:		; preds = %memory_CalculateRealBlockSize1374.exit.i, %entry
+	br i1 undef, label %memory_CalculateRealBlockSize1374.exit.i, label %bb.i.i9
+
+bb.i.i9:		; preds = %bb6.i8
+	br label %memory_CalculateRealBlockSize1374.exit.i
+
+memory_CalculateRealBlockSize1374.exit.i:		; preds = %bb.i.i9, %bb6.i8
+	%0 = phi i32 [ undef, %bb.i.i9 ], [ undef, %bb6.i8 ]		; <i32> [#uses=2]
+	store i32 %0, i32* undef, align 4
+	%1 = urem i32 8184, %0		; <i32> [#uses=1]
+	%2 = sub i32 8188, %1		; <i32> [#uses=1]
+	store i32 %2, i32* undef, align 4
+	br i1 undef, label %memory_Init.exit, label %bb6.i8
+
+memory_Init.exit:		; preds = %memory_CalculateRealBlockSize1374.exit.i
+	br label %bb.i.i
+
+bb.i.i:		; preds = %bb.i.i, %memory_Init.exit
+	br i1 undef, label %symbol_Init.exit, label %bb.i.i
+
+symbol_Init.exit:		; preds = %bb.i.i
+	br label %bb.i.i67
+
+bb.i.i67:		; preds = %bb.i.i67, %symbol_Init.exit
+	br i1 undef, label %symbol_CreatePrecedence3522.exit, label %bb.i.i67
+
+symbol_CreatePrecedence3522.exit:		; preds = %bb.i.i67
+	br label %bb.i.i8.i
+
+bb.i.i8.i:		; preds = %bb.i.i8.i, %symbol_CreatePrecedence3522.exit
+	br i1 undef, label %cont_Create.exit9.i, label %bb.i.i8.i
+
+cont_Create.exit9.i:		; preds = %bb.i.i8.i
+	br label %bb.i.i.i72
+
+bb.i.i.i72:		; preds = %bb.i.i.i72, %cont_Create.exit9.i
+	br i1 undef, label %cont_Init.exit, label %bb.i.i.i72
+
+cont_Init.exit:		; preds = %bb.i.i.i72
+	br label %bb.i103
+
+bb.i103:		; preds = %bb.i103, %cont_Init.exit
+	br i1 undef, label %subs_Init.exit, label %bb.i103
+
+subs_Init.exit:		; preds = %bb.i103
+	br i1 undef, label %bb1.i.i.i80, label %cc_Init.exit
+
+bb1.i.i.i80:		; preds = %subs_Init.exit
+	unreachable
+
+cc_Init.exit:		; preds = %subs_Init.exit
+	br label %bb.i.i375
+
+bb.i.i375:		; preds = %bb.i.i375, %cc_Init.exit
+	br i1 undef, label %bb.i439, label %bb.i.i375
+
+bb.i439:		; preds = %bb.i439, %bb.i.i375
+	br i1 undef, label %opts_DeclareSPASSFlagsAsOptions.exit, label %bb.i439
+
+opts_DeclareSPASSFlagsAsOptions.exit:		; preds = %bb.i439
+	br i1 undef, label %opts_TranslateShortOptDeclarations.exit.i, label %bb.i.i82
+
+bb.i.i82:		; preds = %opts_DeclareSPASSFlagsAsOptions.exit
+	unreachable
+
+opts_TranslateShortOptDeclarations.exit.i:		; preds = %opts_DeclareSPASSFlagsAsOptions.exit
+	br i1 undef, label %list_Length.exit.i.thread.i, label %bb.i.i4.i
+
+list_Length.exit.i.thread.i:		; preds = %opts_TranslateShortOptDeclarations.exit.i
+	br i1 undef, label %bb18.i.i.i, label %bb26.i.i.i
+
+bb.i.i4.i:		; preds = %opts_TranslateShortOptDeclarations.exit.i
+	unreachable
+
+bb18.i.i.i:		; preds = %list_Length.exit.i.thread.i
+	unreachable
+
+bb26.i.i.i:		; preds = %list_Length.exit.i.thread.i
+	br i1 undef, label %bb27.i142, label %opts_GetOptLongOnly.exit.thread97.i
+
+opts_GetOptLongOnly.exit.thread97.i:		; preds = %bb26.i.i.i
+	br label %bb27.i142
+
+bb27.i142:		; preds = %opts_GetOptLongOnly.exit.thread97.i, %bb26.i.i.i
+	br label %bb1.i3.i
+
+bb1.i3.i:		; preds = %bb1.i3.i, %bb27.i142
+	br i1 undef, label %opts_FreeLongOptsArray.exit.i, label %bb1.i3.i
+
+opts_FreeLongOptsArray.exit.i:		; preds = %bb1.i3.i
+	br label %bb.i443
+
+bb.i443:		; preds = %bb.i443, %opts_FreeLongOptsArray.exit.i
+	br i1 undef, label %flag_InitStoreByDefaults3542.exit, label %bb.i443
+
+flag_InitStoreByDefaults3542.exit:		; preds = %bb.i443
+	br i1 undef, label %bb6.i449, label %bb.i503
+
+bb6.i449:		; preds = %flag_InitStoreByDefaults3542.exit
+	unreachable
+
+bb.i503:		; preds = %bb.i503, %flag_InitStoreByDefaults3542.exit
+	br i1 undef, label %flag_CleanStore3464.exit, label %bb.i503
+
+flag_CleanStore3464.exit:		; preds = %bb.i503
+	br i1 undef, label %bb1.i81.i.preheader, label %bb.i173
+
+bb.i173:		; preds = %flag_CleanStore3464.exit
+	unreachable
+
+bb1.i81.i.preheader:		; preds = %flag_CleanStore3464.exit
+	br i1 undef, label %bb1.i64.i.preheader, label %bb5.i179
+
+bb5.i179:		; preds = %bb1.i81.i.preheader
+	unreachable
+
+bb1.i64.i.preheader:		; preds = %bb1.i81.i.preheader
+	br i1 undef, label %dfg_DeleteProofList.exit.i, label %bb.i9.i
+
+bb.i9.i:		; preds = %bb1.i64.i.preheader
+	unreachable
+
+dfg_DeleteProofList.exit.i:		; preds = %bb1.i64.i.preheader
+	br i1 undef, label %term_DeleteTermList621.exit.i, label %bb.i.i62.i
+
+bb.i.i62.i:		; preds = %bb.i.i62.i, %dfg_DeleteProofList.exit.i
+	br i1 undef, label %term_DeleteTermList621.exit.i, label %bb.i.i62.i
+
+term_DeleteTermList621.exit.i:		; preds = %bb.i.i62.i, %dfg_DeleteProofList.exit.i
+	br i1 undef, label %dfg_DFGParser.exit, label %bb.i.i211
+
+bb.i.i211:		; preds = %term_DeleteTermList621.exit.i
+	unreachable
+
+dfg_DFGParser.exit:		; preds = %term_DeleteTermList621.exit.i
+	br label %bb.i513
+
+bb.i513:		; preds = %bb2.i516, %dfg_DFGParser.exit
+	br i1 undef, label %bb2.i516, label %bb1.i514
+
+bb1.i514:		; preds = %bb.i513
+	unreachable
+
+bb2.i516:		; preds = %bb.i513
+	br i1 undef, label %bb.i509, label %bb.i513
+
+bb.i509:		; preds = %bb.i509, %bb2.i516
+	br i1 undef, label %symbol_TransferPrecedence3468.exit511, label %bb.i509
+
+symbol_TransferPrecedence3468.exit511:		; preds = %bb.i509
+	br i1 undef, label %bb20, label %bb21
+
+bb20:		; preds = %symbol_TransferPrecedence3468.exit511
+	unreachable
+
+bb21:		; preds = %symbol_TransferPrecedence3468.exit511
+	br i1 undef, label %cnf_Init.exit, label %bb.i498
+
+bb.i498:		; preds = %bb21
+	unreachable
+
+cnf_Init.exit:		; preds = %bb21
+	br i1 undef, label %bb23, label %bb22
+
+bb22:		; preds = %cnf_Init.exit
+	br i1 undef, label %bb2.i.i496, label %bb.i.i494
+
+bb.i.i494:		; preds = %bb22
+	unreachable
+
+bb2.i.i496:		; preds = %bb22
+	unreachable
+
+bb23:		; preds = %cnf_Init.exit
+	br i1 undef, label %bb28, label %bb24
+
+bb24:		; preds = %bb23
+	unreachable
+
+bb28:		; preds = %bb23
+	br i1 undef, label %bb31, label %bb29
+
+bb29:		; preds = %bb28
+	unreachable
+
+bb31:		; preds = %bb28
+	br i1 undef, label %bb34, label %bb32
+
+bb32:		; preds = %bb31
+	unreachable
+
+bb34:		; preds = %bb31
+	br i1 undef, label %bb83, label %bb66
+
+bb66:		; preds = %bb34
+	unreachable
+
+bb83:		; preds = %bb34
+	br i1 undef, label %bb2.i1668, label %bb.i1667
+
+bb.i1667:		; preds = %bb83
+	unreachable
+
+bb2.i1668:		; preds = %bb83
+	br i1 undef, label %bb5.i205, label %bb3.i204
+
+bb3.i204:		; preds = %bb2.i1668
+	unreachable
+
+bb5.i205:		; preds = %bb2.i1668
+	br i1 undef, label %bb.i206.i, label %ana_AnalyzeSortStructure.exit.i
+
+bb.i206.i:		; preds = %bb5.i205
+	br i1 undef, label %bb1.i207.i, label %ana_AnalyzeSortStructure.exit.i
+
+bb1.i207.i:		; preds = %bb.i206.i
+	br i1 undef, label %bb25.i1801.thread, label %bb.i1688
+
+bb.i1688:		; preds = %bb1.i207.i
+	unreachable
+
+bb25.i1801.thread:		; preds = %bb1.i207.i
+	unreachable
+
+ana_AnalyzeSortStructure.exit.i:		; preds = %bb.i206.i, %bb5.i205
+	br i1 undef, label %bb7.i207, label %bb.i1806
+
+bb.i1806:		; preds = %ana_AnalyzeSortStructure.exit.i
+	br i1 undef, label %bb2.i.i.i1811, label %bb.i.i.i1809
+
+bb.i.i.i1809:		; preds = %bb.i1806
+	unreachable
+
+bb2.i.i.i1811:		; preds = %bb.i1806
+	unreachable
+
+bb7.i207:		; preds = %ana_AnalyzeSortStructure.exit.i
+	br i1 undef, label %bb9.i, label %bb8.i
+
+bb8.i:		; preds = %bb7.i207
+	unreachable
+
+bb9.i:		; preds = %bb7.i207
+	br i1 undef, label %bb23.i, label %bb26.i
+
+bb23.i:		; preds = %bb9.i
+	br i1 undef, label %bb25.i, label %bb24.i
+
+bb24.i:		; preds = %bb23.i
+	br i1 undef, label %sort_SortTheoryIsTrivial.exit.i, label %bb.i2093
+
+bb.i2093:		; preds = %bb.i2093, %bb24.i
+	br label %bb.i2093
+
+sort_SortTheoryIsTrivial.exit.i:		; preds = %bb24.i
+	br i1 undef, label %bb3.i2141, label %bb4.i2143
+
+bb3.i2141:		; preds = %sort_SortTheoryIsTrivial.exit.i
+	unreachable
+
+bb4.i2143:		; preds = %sort_SortTheoryIsTrivial.exit.i
+	br i1 undef, label %bb8.i2178, label %bb5.i2144
+
+bb5.i2144:		; preds = %bb4.i2143
+	br i1 undef, label %bb7.i2177, label %bb1.i28.i
+
+bb1.i28.i:		; preds = %bb5.i2144
+	br i1 undef, label %bb4.i43.i, label %bb2.i.i2153
+
+bb2.i.i2153:		; preds = %bb1.i28.i
+	br i1 undef, label %bb4.i.i33.i, label %bb.i.i30.i
+
+bb.i.i30.i:		; preds = %bb2.i.i2153
+	unreachable
+
+bb4.i.i33.i:		; preds = %bb2.i.i2153
+	br i1 undef, label %bb9.i.i36.i, label %bb5.i.i34.i
+
+bb5.i.i34.i:		; preds = %bb4.i.i33.i
+	unreachable
+
+bb9.i.i36.i:		; preds = %bb4.i.i33.i
+	br i1 undef, label %bb14.i.i.i2163, label %bb10.i.i37.i
+
+bb10.i.i37.i:		; preds = %bb9.i.i36.i
+	unreachable
+
+bb14.i.i.i2163:		; preds = %bb9.i.i36.i
+	br i1 undef, label %sort_LinkPrint.exit.i.i, label %bb15.i.i.i2164
+
+bb15.i.i.i2164:		; preds = %bb14.i.i.i2163
+	unreachable
+
+sort_LinkPrint.exit.i.i:		; preds = %bb14.i.i.i2163
+	unreachable
+
+bb4.i43.i:		; preds = %bb1.i28.i
+	unreachable
+
+bb7.i2177:		; preds = %bb5.i2144
+	unreachable
+
+bb8.i2178:		; preds = %bb4.i2143
+	br i1 undef, label %sort_ApproxStaticSortTheory.exit, label %bb.i5.i2185.preheader
+
+bb.i5.i2185.preheader:		; preds = %bb8.i2178
+	br label %bb.i5.i2185
+
+bb.i5.i2185:		; preds = %bb.i5.i2185, %bb.i5.i2185.preheader
+	br i1 undef, label %sort_ApproxStaticSortTheory.exit, label %bb.i5.i2185
+
+sort_ApproxStaticSortTheory.exit:		; preds = %bb.i5.i2185, %bb8.i2178
+	br label %bb25.i
+
+bb25.i:		; preds = %sort_ApproxStaticSortTheory.exit, %bb23.i
+	unreachable
+
+bb26.i:		; preds = %bb9.i
+	unreachable
+}