Index: lib/CodeGen/LiveDebugValues.cpp
===================================================================
--- lib/CodeGen/LiveDebugValues.cpp
+++ lib/CodeGen/LiveDebugValues.cpp
@@ -201,7 +201,8 @@
                 VarLocInMBB &OutLocs, VarLocMap &VarLocIDs);
 
   bool join(MachineBasicBlock &MBB, VarLocInMBB &OutLocs, VarLocInMBB &InLocs,
-            const VarLocMap &VarLocIDs);
+            const VarLocMap &VarLocIDs,
+            SmallPtrSet<const MachineBasicBlock *, 16> &Visited);
 
   bool ExtendRanges(MachineFunction &MF);
 
@@ -368,7 +369,8 @@
 /// inserting a new DBG_VALUE instruction at the start of the @MBB - if the same
 /// source variable in all the predecessors of @MBB reside in the same location.
 bool LiveDebugValues::join(MachineBasicBlock &MBB, VarLocInMBB &OutLocs,
-                           VarLocInMBB &InLocs, const VarLocMap &VarLocIDs) {
+                           VarLocInMBB &InLocs, const VarLocMap &VarLocIDs,
+                           SmallPtrSet<const MachineBasicBlock *, 16> &Visited) {
   DEBUG(dbgs() << "join MBB: " << MBB.getName() << "\n");
   bool Changed = false;
 
@@ -376,21 +378,32 @@
 
   // For all predecessors of this MBB, find the set of VarLocs that
   // can be joined.
+  int NumVisited = 0;
   for (auto p : MBB.predecessors()) {
+    // Ignore unvisited predecessor blocks.  As we are processing
+    // the blocks in reverse post-order any unvisited block can
+    // be considered to not remove any incoming values.
+    if (!Visited.count(p))
+      continue;
     auto OL = OutLocs.find(p);
     // Join is null in case of empty OutLocs from any of the pred.
     if (OL == OutLocs.end())
       return false;
 
-    // Just copy over the Out locs to incoming locs for the first predecessor.
-    if (p == *MBB.pred_begin()) {
+    // Just copy over the Out locs to incoming locs for the first visited
+    // predecessor, and for all other predecessors join the Out locs.
+    if (!NumVisited)
       InLocsT = OL->second;
-      continue;
-    }
-    // Join with this predecessor.
-    InLocsT &= OL->second;
+    else
+      InLocsT &= OL->second;
+    NumVisited++;
   }
 
+  // As we are processing blocks in reverse post-order we
+  // should have processed at least one predecessor, unless it
+  // is the entry block which has no predecessor.
+  assert((NumVisited || MBB.pred_empty()) &&
+         "Should have processed at least one predecessor");
   if (InLocsT.empty())
     return false;
 
@@ -463,6 +476,7 @@
   // To solve it, we perform join() and transfer() using the two worklist method
   // until the ranges converge.
   // Ranges have converged when both worklists are empty.
+  SmallPtrSet<const MachineBasicBlock *, 16> Visited;
   while (!Worklist.empty() || !Pending.empty()) {
     // We track what is on the pending worklist to avoid inserting the same
     // thing twice.  We could avoid this with a custom priority queue, but this
@@ -472,8 +486,8 @@
     while (!Worklist.empty()) {
       MachineBasicBlock *MBB = OrderToBB[Worklist.top()];
       Worklist.pop();
-      MBBJoined = join(*MBB, OutLocs, InLocs, VarLocIDs);
-
+      MBBJoined = join(*MBB, OutLocs, InLocs, VarLocIDs, Visited);
+      Visited.insert(MBB);
       if (MBBJoined) {
         MBBJoined = false;
         Changed = true;
Index: test/CodeGen/ARM/dbg-range-extension.mir
===================================================================
--- test/CodeGen/ARM/dbg-range-extension.mir
+++ test/CodeGen/ARM/dbg-range-extension.mir
@@ -0,0 +1,282 @@
+# RUN: llc -mtriple=arm-eabi -run-pass=livedebugvalues %s -o - | FileCheck %s
+#
+# Check that the debug information for variables are propagated into the correct blocks.
+#
+# Generated from the C source:
+#
+# int func2(int,  int);
+# void func(int a) {
+#   int b = func2(10, 11);
+#   if (a) {
+#     int c = func2(12, 13);
+#     for(int i = 1; i < a; i++) {
+#       func2(i, i+b);
+#     }
+#     func2(b,c);
+#   }
+#   func2(b,a);
+# }
+
+# CHECK: [[VAR_A:![0-9]+]] = !DILocalVariable(name: "a",
+# CHECK: [[VAR_B:![0-9]+]] = !DILocalVariable(name: "b",
+# CHECK: [[VAR_C:![0-9]+]] = !DILocalVariable(name: "c",
+# CHECK: [[VAR_I:![0-9]+]] = !DILocalVariable(name: "i",
+
+# CHECK: bb.0.entry
+# CHECK: DBG_VALUE debug-use %r0, debug-use _, [[VAR_A]]
+# CHECK: DBG_VALUE debug-use [[REG_A:%r[0-9]+]], debug-use _, [[VAR_A]]
+# CHECK: DBG_VALUE debug-use [[REG_B:%r[0-9]+]], debug-use _, [[VAR_B]]
+
+# CHECK: bb.1.if.then
+# CHECK: DBG_VALUE debug-use [[REG_B]], debug-use _, [[VAR_B]]
+# CHECK: DBG_VALUE debug-use [[REG_A]], debug-use _, [[VAR_A]]
+# CHECK: DBG_VALUE debug-use [[REG_C:%r[0-9]+]], debug-use _, [[VAR_C]]
+# CHECK: DBG_VALUE 1, 0, [[VAR_I]]
+
+# CHECK: bb.2.for.body
+# CHECK: DBG_VALUE debug-use [[REG_I:%r[0-9]+]], debug-use _, [[VAR_I]]
+# CHECK: DBG_VALUE debug-use [[REG_C]], debug-use _, [[VAR_C]]
+# CHECK: DBG_VALUE debug-use [[REG_B]], debug-use _, [[VAR_B]]
+# CHECK: DBG_VALUE debug-use [[REG_A]], debug-use _, [[VAR_A]]
+# CHECK: DBG_VALUE debug-use [[REG_I]], debug-use _, [[VAR_I]]
+
+# CHECK: bb.3.for.cond
+# CHECK: DBG_VALUE debug-use [[REG_C]], debug-use _, [[VAR_C]]
+# CHECK: DBG_VALUE debug-use [[REG_B]], debug-use _, [[VAR_B]]
+# CHECK: DBG_VALUE debug-use [[REG_A]], debug-use _, [[VAR_A]]
+# CHECK: DBG_VALUE debug-use [[REG_I]], debug-use _, [[VAR_I]]
+
+# CHECK: bb.4.for.cond.cleanup
+# CHECK: DBG_VALUE debug-use [[REG_I]], debug-use _, [[VAR_I]]
+# CHECK: DBG_VALUE debug-use [[REG_C]], debug-use _, [[VAR_C]]
+# CHECK: DBG_VALUE debug-use [[REG_B]], debug-use _, [[VAR_B]]
+# CHECK: DBG_VALUE debug-use [[REG_A]], debug-use _, [[VAR_A]]
+
+# CHECK: bb.5.if.end
+# CHECK: DBG_VALUE debug-use [[REG_B]], debug-use _, [[VAR_B]]
+# CHECK: DBG_VALUE debug-use [[REG_A]], debug-use _, [[VAR_A]]
+--- |
+  ; ModuleID = '/data/kwalker/work/OpenSource-llvm/llvm/test/CodeGen/ARM/dbg-range-extension.ll'
+  source_filename = "/data/kwalker/work/OpenSource-llvm/llvm/test/CodeGen/ARM/dbg-range-extension.ll"
+  target datalayout = "e-m:e-p:32:32-i64:64-v128:64:128-a:0:32-n32-S64"
+  target triple = "arm---eabi"
+  
+  ; Function Attrs: minsize nounwind optsize
+  define void @func(i32 %a) local_unnamed_addr #0 !dbg !8 {
+  entry:
+    tail call void @llvm.dbg.value(metadata i32 %a, i64 0, metadata !13, metadata !20), !dbg !21
+    %call = tail call i32 @func2(i32 10, i32 11) #0, !dbg !22
+    tail call void @llvm.dbg.value(metadata i32 %call, i64 0, metadata !14, metadata !20), !dbg !23
+    %tobool = icmp eq i32 %a, 0, !dbg !24
+    br i1 %tobool, label %if.end, label %if.then, !dbg !25
+  
+  if.then:                                          ; preds = %entry
+    %call1 = tail call i32 @func2(i32 12, i32 13) #0, !dbg !26
+    tail call void @llvm.dbg.value(metadata i32 %call1, i64 0, metadata !15, metadata !20), !dbg !27
+    tail call void @llvm.dbg.value(metadata i32 1, i64 0, metadata !18, metadata !20), !dbg !28
+    br label %for.cond, !dbg !29
+  
+  for.cond:                                         ; preds = %for.body, %if.then
+    %i.0 = phi i32 [ 1, %if.then ], [ %inc, %for.body ]
+    tail call void @llvm.dbg.value(metadata i32 %i.0, i64 0, metadata !18, metadata !20), !dbg !28
+    %cmp = icmp slt i32 %i.0, %a, !dbg !30
+    br i1 %cmp, label %for.body, label %for.cond.cleanup, !dbg !33
+  
+  for.cond.cleanup:                                 ; preds = %for.cond
+    %call3 = tail call i32 @func2(i32 %call, i32 %call1) #0, !dbg !34
+    br label %if.end, !dbg !35
+  
+  for.body:                                         ; preds = %for.cond
+    %0 = add i32 %call, %i.0, !dbg !36
+    %call2 = tail call i32 @func2(i32 %i.0, i32 %0) #0, !dbg !36
+    %inc = add nuw nsw i32 %i.0, 1, !dbg !38
+    tail call void @llvm.dbg.value(metadata i32 %inc, i64 0, metadata !18, metadata !20), !dbg !28
+    br label %for.cond, !dbg !40, !llvm.loop !41
+  
+  if.end:                                           ; preds = %for.cond.cleanup, %entry
+    %call4 = tail call i32 @func2(i32 %call, i32 %a) #0, !dbg !43
+    ret void, !dbg !44
+  }
+  
+  ; Function Attrs: minsize optsize
+  declare i32 @func2(i32, i32) local_unnamed_addr #1
+  
+  ; Function Attrs: nounwind readnone
+  declare void @llvm.dbg.value(metadata, i64, metadata, metadata) #2
+  
+  ; Function Attrs: nounwind
+  declare void @llvm.stackprotector(i8*, i8**) #3
+  
+  attributes #0 = { minsize nounwind optsize }
+  attributes #1 = { minsize optsize }
+  attributes #2 = { nounwind readnone }
+  attributes #3 = { nounwind }
+  
+  !llvm.dbg.cu = !{!0}
+  !llvm.module.flags = !{!3, !4, !5, !6}
+  !llvm.ident = !{!7}
+  
+  !0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
+  !1 = !DIFile(filename: "loop.c", directory: "/tmp")
+  !2 = !{}
+  !3 = !{i32 2, !"Dwarf Version", i32 4}
+  !4 = !{i32 2, !"Debug Info Version", i32 3}
+  !5 = !{i32 1, !"wchar_size", i32 4}
+  !6 = !{i32 1, !"min_enum_size", i32 4}
+  !7 = !{!"clang version 4.0.0 (http://llvm.org/git/clang.git b8f10df3679b36f51e1de7c4351b82d297825089) (http://llvm.org/git/llvm.git c2a5d16d1e3b8c49f5bbb1ff87a76ac4f88edb89)"}
+  !8 = distinct !DISubprogram(name: "func", scope: !1, file: !1, line: 2, type: !9, isLocal: false, isDefinition: true, scopeLine: 2, flags: DIFlagPrototyped, isOptimized: true, unit: !0, variables: !12)
+  !9 = !DISubroutineType(types: !10)
+  !10 = !{null, !11}
+  !11 = !DIBasicType(name: "int", size: 32, align: 32, encoding: DW_ATE_signed)
+  !12 = !{!13, !14, !15, !18}
+  !13 = !DILocalVariable(name: "a", arg: 1, scope: !8, file: !1, line: 2, type: !11)
+  !14 = !DILocalVariable(name: "b", scope: !8, file: !1, line: 3, type: !11)
+  !15 = !DILocalVariable(name: "c", scope: !16, file: !1, line: 5, type: !11)
+  !16 = distinct !DILexicalBlock(scope: !17, file: !1, line: 4, column: 9)
+  !17 = distinct !DILexicalBlock(scope: !8, file: !1, line: 4, column: 6)
+  !18 = !DILocalVariable(name: "i", scope: !19, file: !1, line: 6, type: !11)
+  !19 = distinct !DILexicalBlock(scope: !16, file: !1, line: 6, column: 3)
+  !20 = !DIExpression()
+  !21 = !DILocation(line: 2, column: 15, scope: !8)
+  !22 = !DILocation(line: 3, column: 17, scope: !8)
+  !23 = !DILocation(line: 3, column: 13, scope: !8)
+  !24 = !DILocation(line: 4, column: 6, scope: !17)
+  !25 = !DILocation(line: 4, column: 6, scope: !8)
+  !26 = !DILocation(line: 5, column: 11, scope: !16)
+  !27 = !DILocation(line: 5, column: 7, scope: !16)
+  !28 = !DILocation(line: 6, column: 11, scope: !19)
+  !29 = !DILocation(line: 6, column: 7, scope: !19)
+  !30 = !DILocation(line: 6, column: 20, scope: !31)
+  !31 = !DILexicalBlockFile(scope: !32, file: !1, discriminator: 1)
+  !32 = distinct !DILexicalBlock(scope: !19, file: !1, line: 6, column: 3)
+  !33 = !DILocation(line: 6, column: 3, scope: !31)
+  !34 = !DILocation(line: 9, column: 3, scope: !16)
+  !35 = !DILocation(line: 10, column: 2, scope: !16)
+  !36 = !DILocation(line: 7, column: 4, scope: !37)
+  !37 = distinct !DILexicalBlock(scope: !32, file: !1, line: 6, column: 30)
+  !38 = !DILocation(line: 6, column: 26, scope: !39)
+  !39 = !DILexicalBlockFile(scope: !32, file: !1, discriminator: 3)
+  !40 = !DILocation(line: 6, column: 3, scope: !39)
+  !41 = distinct !{!41, !42}
+  !42 = !DILocation(line: 6, column: 3, scope: !16)
+  !43 = !DILocation(line: 11, column: 2, scope: !8)
+  !44 = !DILocation(line: 12, column: 1, scope: !8)
+
+...
+---
+name:            func
+alignment:       2
+exposesReturnsTwice: false
+legalized:       false
+regBankSelected: false
+selected:        false
+tracksRegLiveness: false
+liveins:         
+  - { reg: '%r0' }
+calleeSavedRegisters: [ '%lr', '%d8', '%d9', '%d10', '%d11', '%d12', '%d13', 
+                        '%d14', '%d15', '%q4', '%q5', '%q6', '%q7', '%r4', 
+                        '%r5', '%r6', '%r7', '%r8', '%r9', '%r10', '%r11', 
+                        '%s16', '%s17', '%s18', '%s19', '%s20', '%s21', 
+                        '%s22', '%s23', '%s24', '%s25', '%s26', '%s27', 
+                        '%s28', '%s29', '%s30', '%s31', '%d8_d10', '%d9_d11', 
+                        '%d10_d12', '%d11_d13', '%d12_d14', '%d13_d15', 
+                        '%q4_q5', '%q5_q6', '%q6_q7', '%q4_q5_q6_q7', '%r4_r5', 
+                        '%r6_r7', '%r8_r9', '%r10_r11', '%d8_d9_d10', '%d9_d10_d11', 
+                        '%d10_d11_d12', '%d11_d12_d13', '%d12_d13_d14', 
+                        '%d13_d14_d15', '%d8_d10_d12', '%d9_d11_d13', '%d10_d12_d14', 
+                        '%d11_d13_d15', '%d8_d10_d12_d14', '%d9_d11_d13_d15', 
+                        '%d9_d10', '%d11_d12', '%d13_d14', '%d9_d10_d11_d12', 
+                        '%d11_d12_d13_d14' ]
+frameInfo:       
+  isFrameAddressTaken: false
+  isReturnAddressTaken: false
+  hasStackMap:     false
+  hasPatchPoint:   false
+  stackSize:       24
+  offsetAdjustment: 0
+  maxAlignment:    4
+  adjustsStack:    true
+  hasCalls:        true
+  maxCallFrameSize: 0
+  hasOpaqueSPAdjustment: false
+  hasVAStart:      false
+  hasMustTailInVarArgFunc: false
+stack:           
+  - { id: 0, type: spill-slot, offset: -4, size: 4, alignment: 4, callee-saved-register: '%lr' }
+  - { id: 1, type: spill-slot, offset: -8, size: 4, alignment: 4, callee-saved-register: '%r11' }
+  - { id: 2, type: spill-slot, offset: -12, size: 4, alignment: 4, callee-saved-register: '%r7' }
+  - { id: 3, type: spill-slot, offset: -16, size: 4, alignment: 4, callee-saved-register: '%r6' }
+  - { id: 4, type: spill-slot, offset: -20, size: 4, alignment: 4, callee-saved-register: '%r5' }
+  - { id: 5, type: spill-slot, offset: -24, size: 4, alignment: 4, callee-saved-register: '%r4' }
+body:             |
+  bb.0.entry:
+    successors: %bb.5.if.end, %bb.1.if.then
+    liveins: %r0, %r4, %r5, %r6, %r7, %r11, %lr
+  
+    %sp = frame-setup STMDB_UPD %sp, 14, _, killed %r4, killed %r5, killed %r6, killed %r7, killed %r11, killed %lr
+    frame-setup CFI_INSTRUCTION def_cfa_offset 24
+    frame-setup CFI_INSTRUCTION offset %lr, -4
+    frame-setup CFI_INSTRUCTION offset %r11, -8
+    frame-setup CFI_INSTRUCTION offset %r7, -12
+    frame-setup CFI_INSTRUCTION offset %r6, -16
+    frame-setup CFI_INSTRUCTION offset %r5, -20
+    frame-setup CFI_INSTRUCTION offset %r4, -24
+    DBG_VALUE debug-use %r0, debug-use _, !13, !20, debug-location !21
+    %r4 = MOVr killed %r0, 14, _, _
+    DBG_VALUE debug-use %r4, debug-use _, !13, !20, debug-location !21
+    %r0 = MOVi 10, 14, _, _, debug-location !22
+    %r1 = MOVi 11, 14, _, _, debug-location !22
+    BL @func2, csr_aapcs, implicit-def dead %lr, implicit %sp, implicit killed %r0, implicit killed %r1, implicit-def %sp, implicit-def %r0, debug-location !22
+    %r5 = MOVr killed %r0, 14, _, _, debug-location !22
+    DBG_VALUE debug-use %r5, debug-use _, !14, !20, debug-location !23
+    CMPri %r4, 0, 14, _, implicit-def %cpsr, debug-location !25
+    Bcc %bb.5.if.end, 0, killed %cpsr
+  
+  bb.1.if.then:
+    successors: %bb.3.for.cond
+    liveins: %r4, %r5
+  
+    %r0 = MOVi 12, 14, _, _, debug-location !26
+    %r1 = MOVi 13, 14, _, _, debug-location !26
+    BL @func2, csr_aapcs, implicit-def dead %lr, implicit %sp, implicit killed %r0, implicit killed %r1, implicit-def %sp, implicit-def %r0, debug-location !26
+    %r6 = MOVr killed %r0, 14, _, _, debug-location !26
+    DBG_VALUE debug-use %r6, debug-use _, !15, !20, debug-location !27
+    %r7 = MOVi 1, 14, _, _
+    DBG_VALUE 1, 0, !18, !20, debug-location !28
+    B %bb.3.for.cond
+  
+  bb.2.for.body:
+    successors: %bb.3.for.cond
+    liveins: %r4, %r5, %r6, %r7
+  
+    %r1 = ADDrr %r5, %r7, 14, _, _, debug-location !36
+    %r0 = MOVr %r7, 14, _, _, debug-location !36
+    BL @func2, csr_aapcs, implicit-def dead %lr, implicit %sp, implicit killed %r0, implicit killed %r1, implicit-def %sp, implicit-def dead %r0, debug-location !36
+    %r7 = ADDri killed %r7, 1, 14, _, _, debug-location !38
+    DBG_VALUE debug-use %r7, debug-use _, !18, !20, debug-location !28
+  
+  bb.3.for.cond:
+    successors: %bb.2.for.body, %bb.4.for.cond.cleanup
+    liveins: %r4, %r5, %r6, %r7
+  
+    DBG_VALUE debug-use %r7, debug-use _, !18, !20, debug-location !28
+    CMPrr %r7, %r4, 14, _, implicit-def %cpsr, debug-location !33
+    Bcc %bb.2.for.body, 11, killed %cpsr, debug-location !33
+  
+  bb.4.for.cond.cleanup:
+    successors: %bb.5.if.end
+    liveins: %r4, %r5, %r6
+  
+    %r0 = MOVr %r5, 14, _, _, debug-location !34
+    %r1 = MOVr killed %r6, 14, _, _, debug-location !34
+    BL @func2, csr_aapcs, implicit-def dead %lr, implicit %sp, implicit killed %r0, implicit killed %r1, implicit-def %sp, implicit-def dead %r0, debug-location !34
+  
+  bb.5.if.end:
+    liveins: %r4, %r5
+  
+    %r0 = MOVr killed %r5, 14, _, _, debug-location !43
+    %r1 = MOVr killed %r4, 14, _, _, debug-location !43
+    %sp = LDMIA_UPD %sp, 14, _, def %r4, def %r5, def %r6, def %r7, def %r11, def %lr, debug-location !43
+    TAILJMPd @func2, implicit %sp, implicit %sp, implicit killed %r0, implicit killed %r1, debug-location !43
+
+...