Index: lib/CodeGen/CodeGenPrepare.cpp
===================================================================
--- lib/CodeGen/CodeGenPrepare.cpp
+++ lib/CodeGen/CodeGenPrepare.cpp
@@ -359,6 +359,7 @@
     bool optimizeSwitchInst(SwitchInst *SI);
     bool optimizeExtractElementInst(Instruction *Inst);
     bool dupRetToEnableTailCallOpts(BasicBlock *BB);
+    bool fixupDbgValue(Instruction *I);
     bool placeDbgValues(Function &F);
     bool canFormExtLd(const SmallVectorImpl<Instruction *> &MovedExts,
                       LoadInst *&LI, Instruction *&Inst, bool HasPromoted);
@@ -1856,6 +1857,8 @@
     case Intrinsic::ctlz:
       // If counting zeros is expensive, try to avoid it.
       return despeculateCountZeros(II, TLI, DL, ModifiedDT);
+    case Intrinsic::dbg_value:
+      return fixupDbgValue(II);
     }
 
     if (TLI) {
@@ -6981,6 +6984,28 @@
   return MadeChange;
 }
 
+// Some CGP optimizations may move or alter what's computed in a block. Check
+// whether a dbg.value intrinsic could be pointed at a more appropriate operand.
+bool CodeGenPrepare::fixupDbgValue(Instruction *I) {
+  assert(isa<DbgValueInst>(I));
+  DbgValueInst &DVI = *cast<DbgValueInst>(I);
+
+  // Does this dbg.value refer to a sunk address calculation?
+  Value *Location = DVI.getVariableLocation();
+  WeakTrackingVH SunkAddrVH = SunkAddrs[Location];
+  Value *SunkAddr = SunkAddrVH.pointsToAliveValue() ? SunkAddrVH : nullptr;
+  if (SunkAddr) {
+    // Point dbg.value at locally computed address, which should give the best
+    // opportunity to be accurately lowered. This update may change the type of
+    // pointer being referred to; however this makes no difference to debugging
+    // information, and we can't generate bitcasts that may affect codegen.
+    DVI.setOperand(0, MetadataAsValue::get(DVI.getContext(),
+                                           ValueAsMetadata::get(SunkAddr)));
+    return true;
+  }
+  return false;
+}
+
 // llvm.dbg.value is far away from the value then iSel may not be able
 // handle it properly. iSel will drop llvm.dbg.value if it can not
 // find a node corresponding to the value.
Index: test/DebugInfo/Generic/codegenprep-addrsink.ll
===================================================================
--- /dev/null
+++ test/DebugInfo/Generic/codegenprep-addrsink.ll
@@ -0,0 +1,70 @@
+; RUN: llc -start-before=codegenprepare -stop-after=codegenprepare %s -o - | FileCheck %s
+;
+; CGP duplicates address calculation into each basic block that contains loads
+; or stores, so that they can be folded into instruction memory operands for
+; example. dbg.value's should be redirected to identify such local address
+; computations, to give the best opportunity for variable locations to be
+; preserved.
+; This test has two dbg.values in it, one before and one after the relevant
+; memory instruction. Test that the one before does _not_ get updated (as that
+; would either make it use-before-def or shift when the variable appears), and
+; that the dbg.value after the memory instruction does get updated.
+;
+; Due to placeDbgValues, the dbg.values currently get shifted up a few
+; instructions.
+
+define dso_local i8 @foo(i32 *%p, i32 %cond) !dbg !7 {
+entry:
+; The first dbg.value of %arith, in the 'next' block, will be moved up here
+; by placeDbgValues,
+; CHECK-LABEL: entry:
+; CHECK:       dbg.value(metadata i8* %arith, metadata ![[DIVAR:[0-9]+]],
+; CHECK-SAME:    metadata !DIExpression()
+  %casted = bitcast i32 *%p to i8*
+  %arith = getelementptr i8, i8 *%casted, i32 3
+  %load1 = load i8, i8 *%arith
+  %cmpresult = icmp eq i32 %cond, 0
+  br i1 %cmpresult, label %next, label %ret
+
+next:
+; Address calcs should be duplicated into this block. One dbg.value should be
+; updated, and the other should not.
+; CHECK-LABEL: next:
+; CHECK:       %[[CASTVAR:[0-9a-zA-Z]+]] = bitcast i32* %p to i8*
+; CHECK-NEXT:  %[[GEPVAR:[0-9a-zA-Z]+]] = getelementptr i8, i8* %[[CASTVAR]],
+; CHECK-SAME:                             i64 3
+; CHECK-NEXT:  call void @llvm.dbg.value(metadata i8* %[[GEPVAR]],
+; CHECK-SAME:                            metadata ![[DIVAR]],
+; CHECK-NEXT:  %loaded = load i8, i8* %[[GEPVAR]]
+  call void @llvm.dbg.value(metadata i8 *%arith, metadata !12, metadata !DIExpression()), !dbg !14
+  %loaded = load i8, i8 *%arith
+  call void @llvm.dbg.value(metadata i8 *%arith, metadata !12, metadata !DIExpression()), !dbg !14
+  ret i8 %loaded
+
+ret:
+  ret i8 0
+}
+
+; CHECK: ![[DIVAR]] = !DILocalVariable(name: "p",
+
+declare void @llvm.dbg.value(metadata, metadata, metadata)
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4, !5}
+!llvm.ident = !{!6}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer: "clang", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, nameTableKind: None)
+!1 = !DIFile(filename: "test.cpp", directory: ".")
+!2 = !{}
+!3 = !{i32 2, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{i32 1, !"wchar_size", i32 4}
+!6 = !{!"clang version 8.0.0 (trunk 348209)"}
+!7 = distinct !DISubprogram(name: "foo", linkageName: "foo", scope: !1, file: !1, line: 4, type: !8, scopeLine: 5, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !11)
+!8 = !DISubroutineType(types: !9)
+!9 = !{null, !10}
+!10 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!11 = !{!12}
+!12 = !DILocalVariable(name: "p", arg: 1, scope: !7, file: !1, line: 4, type: !10)
+!14 = !DILocation(line: 4, column: 15, scope: !7)
+!20 = distinct !DILexicalBlock(scope: !7, file: !1, line: 8, column: 7)