Index: include/llvm/CodeGen/MachineSSAUpdater.h
===================================================================
--- include/llvm/CodeGen/MachineSSAUpdater.h
+++ include/llvm/CodeGen/MachineSSAUpdater.h
@@ -103,6 +103,11 @@
   /// for the use's block will be considered to be below it.
   void RewriteUse(MachineOperand &U);
 
+  // TODO This is unimplemented.
+  /// UpdatePHIDebugInfo - Insert dbg.value calls to newly created PHI nodes
+  /// so that debug info can be kept up-to-date. Unimplemented.
+  void UpdatePHIDebugInfo(MachineInstr *PHI) { }
+
 private:
   unsigned GetValueAtEndOfBlockInternal(MachineBasicBlock *BB);
 
Index: include/llvm/Transforms/Utils/SSAUpdater.h
===================================================================
--- include/llvm/Transforms/Utils/SSAUpdater.h
+++ include/llvm/Transforms/Utils/SSAUpdater.h
@@ -119,6 +119,10 @@
   /// inserted values.
   void RewriteUseAfterInsertions(Use &U);
 
+  /// UpdatePHIDebugInfo - Insert dbg.value calls to newly created PHI nodes
+  /// so that debug info can be kept up-to-date.
+  void UpdatePHIDebugInfo(PHINode *PHI);
+
 private:
   Value *GetValueAtEndOfBlockInternal(BasicBlock *BB);
 };
Index: include/llvm/Transforms/Utils/SSAUpdaterImpl.h
===================================================================
--- include/llvm/Transforms/Utils/SSAUpdaterImpl.h
+++ include/llvm/Transforms/Utils/SSAUpdaterImpl.h
@@ -366,6 +366,7 @@
         Traits::AddPHIOperand(PHI, PredInfo->AvailableVal, Pred);
       }
 
+      Updater->UpdatePHIDebugInfo(PHI);
       DEBUG(dbgs() << "  Inserted PHI: " << *PHI << "\n");
 
       // If the client wants to know about all new instructions, tell it.
Index: lib/Transforms/Utils/SSAUpdater.cpp
===================================================================
--- lib/Transforms/Utils/SSAUpdater.cpp
+++ lib/Transforms/Utils/SSAUpdater.cpp
@@ -23,6 +23,7 @@
 #include "llvm/IR/DebugLoc.h"
 #include "llvm/IR/Instruction.h"
 #include "llvm/IR/Instructions.h"
+#include "llvm/IR/IntrinsicInst.h"
 #include "llvm/IR/Module.h"
 #include "llvm/IR/Use.h"
 #include "llvm/IR/Value.h"
@@ -176,6 +177,7 @@
   if (const Instruction *I = BB->getFirstNonPHI())
       DL = I->getDebugLoc();
   InsertedPHI->setDebugLoc(DL);
+  UpdatePHIDebugInfo(InsertedPHI);
 
   // If the client wants to know about all new instructions, tell it.
   if (InsertedPHIs) InsertedPHIs->push_back(InsertedPHI);
@@ -213,6 +215,38 @@
   U.set(V);
 }
 
+void SSAUpdater::UpdatePHIDebugInfo(PHINode *PHI) {
+  LLVMContext &C = PHI->getParent()->getContext();
+
+  for (unsigned i = 0; i < PHI->getNumOperands(); ++i) {
+    Value *Val = PHI->getOperand(i);
+
+    if (isa<Constant>(Val))
+      continue;
+
+    // If the value is a non constant and it has debug info attached, create
+    // another debug value for this PHI so that the debug value is kept
+    // up-to-date.
+    if (auto *VAM = ValueAsMetadata::getIfExists(Val)) {
+      if (auto *MAV = MetadataAsValue::getIfExists(C, VAM)) {
+        for (auto UI = MAV->use_begin(), E = MAV->use_end(); UI != E;) {
+          // Grab the use before incrementing the iterator. Otherwise,
+          // altering the Use will invalidate the iterator.
+          Use &U = *UI++;
+          auto *UserInst = dyn_cast<DbgInfoIntrinsic>(U.getUser());
+          if (!UserInst)
+            continue;
+          Instruction *Clone = UserInst->clone();
+          auto PhiMAV = MetadataAsValue::get(C, ValueAsMetadata::get(PHI));
+          Clone->setOperand(0, PhiMAV);
+          BasicBlock *BB = PHI->getParent();
+          Clone->insertBefore(BB->getFirstNonPHIOrDbgOrLifetime());
+        }
+      }
+    }
+  }
+}
+
 namespace llvm {
 
 template<>
Index: test/Transforms/Util/phi-dbgvalue.ll
===================================================================
--- /dev/null
+++ test/Transforms/Util/phi-dbgvalue.ll
@@ -0,0 +1,79 @@
+; RUN: opt -S -loop-rotate < %s | FileCheck %s
+
+;CHECK-LABEL: func
+;CHECK-LABEL: entry
+;CHECK-NEXT: tail call void @llvm.dbg.value(metadata i32 %a
+;CHECK-NEXT: tail call void @llvm.dbg.value(metadata i32 1, i64 0, metadata !13, metadata !11), !dbg !15
+;CHECK-LABEL: for.body:
+;CHECK-NEXT: [[I:%.*]] = phi i32 [ 1, %entry ], [ %inc, %for.body ]
+;CHECK-NEXT: tail call void @llvm.dbg.value(metadata i32 [[I]], i64 0, metadata !13, metadata !11), !dbg !15
+
+; Function Attrs: noinline nounwind
+define void @func(i32 %a) local_unnamed_addr #0 !dbg !6 {
+entry:
+  tail call void @llvm.dbg.value(metadata i32 %a, i64 0, metadata !10, metadata !11), !dbg !12
+  tail call void @llvm.dbg.value(metadata i32 1, i64 0, metadata !13, metadata !11), !dbg !15
+  br label %for.cond, !dbg !16
+
+for.cond:                                         ; preds = %for.body, %entry
+  %i.0 = phi i32 [ 1, %entry ], [ %inc, %for.body ]
+  tail call void @llvm.dbg.value(metadata i32 %i.0, i64 0, metadata !13, metadata !11), !dbg !15
+  %cmp = icmp slt i32 %i.0, 10, !dbg !17
+  br i1 %cmp, label %for.body, label %for.end, !dbg !20
+
+for.body:                                         ; preds = %for.cond
+  %add = add nsw i32 %i.0, %a, !dbg !22
+  %call = tail call i32 @func2(i32 %i.0, i32 %add) #3, !dbg !24
+  %inc = add nsw i32 %i.0, 1, !dbg !25
+  tail call void @llvm.dbg.value(metadata i32 %inc, i64 0, metadata !13, metadata !11), !dbg !15
+  br label %for.cond, !dbg !27, !llvm.loop !28
+
+for.end:                                          ; preds = %for.cond
+  ret void, !dbg !31
+}
+
+declare i32 @func2(i32, i32) local_unnamed_addr
+
+; Function Attrs: nounwind readnone
+declare void @llvm.dbg.value(metadata, i64, metadata, metadata) #2
+
+attributes #0 = { noinline nounwind }
+attributes #2 = { nounwind readnone }
+attributes #3 = { nounwind }
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4}
+!llvm.ident = !{!5}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 5.0.0 (http://llvm.org/git/clang.git 0f3ed908c1f13f83da4b240f7595eb8d05e0a754) (http://llvm.org/git/llvm.git 8e270f5a6b8ceb0f3ac3ef1ffb83c5e29b44ae68)", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
+!1 = !DIFile(filename: "debug-phi.c", directory: "/work/projects/src/tests/debug")
+!2 = !{}
+!3 = !{i32 2, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{!"clang version 5.0.0 (http://llvm.org/git/clang.git 0f3ed908c1f13f83da4b240f7595eb8d05e0a754) (http://llvm.org/git/llvm.git 8e270f5a6b8ceb0f3ac3ef1ffb83c5e29b44ae68)"}
+!6 = distinct !DISubprogram(name: "func", scope: !1, file: !1, line: 2, type: !7, isLocal: false, isDefinition: true, scopeLine: 2, flags: DIFlagPrototyped, isOptimized: false, unit: !0, variables: !2)
+!7 = !DISubroutineType(types: !8)
+!8 = !{null, !9}
+!9 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!10 = !DILocalVariable(name: "a", arg: 1, scope: !6, file: !1, line: 2, type: !9)
+!11 = !DIExpression()
+!12 = !DILocation(line: 2, column: 15, scope: !6)
+!13 = !DILocalVariable(name: "i", scope: !14, file: !1, line: 3, type: !9)
+!14 = distinct !DILexicalBlock(scope: !6, file: !1, line: 3, column: 3)
+!15 = !DILocation(line: 3, column: 11, scope: !14)
+!16 = !DILocation(line: 3, column: 7, scope: !14)
+!17 = !DILocation(line: 3, column: 20, scope: !18)
+!18 = !DILexicalBlockFile(scope: !19, file: !1, discriminator: 1)
+!19 = distinct !DILexicalBlock(scope: !14, file: !1, line: 3, column: 3)
+!20 = !DILocation(line: 3, column: 3, scope: !21)
+!21 = !DILexicalBlockFile(scope: !14, file: !1, discriminator: 1)
+!22 = !DILocation(line: 4, column: 15, scope: !23)
+!23 = distinct !DILexicalBlock(scope: !19, file: !1, line: 3, column: 31)
+!24 = !DILocation(line: 4, column: 5, scope: !23)
+!25 = !DILocation(line: 3, column: 27, scope: !26)
+!26 = !DILexicalBlockFile(scope: !19, file: !1, discriminator: 2)
+!27 = !DILocation(line: 3, column: 3, scope: !26)
+!28 = distinct !{!28, !29, !30}
+!29 = !DILocation(line: 3, column: 3, scope: !14)
+!30 = !DILocation(line: 5, column: 3, scope: !14)
+!31 = !DILocation(line: 6, column: 1, scope: !6)