Index: llvm/trunk/lib/Transforms/IPO/DeadArgumentElimination.cpp
===================================================================
--- llvm/trunk/lib/Transforms/IPO/DeadArgumentElimination.cpp
+++ llvm/trunk/lib/Transforms/IPO/DeadArgumentElimination.cpp
@@ -24,7 +24,6 @@
 #include "llvm/IR/Attributes.h"
 #include "llvm/IR/BasicBlock.h"
 #include "llvm/IR/CallSite.h"
-#include "llvm/IR/Constant.h"
 #include "llvm/IR/Constants.h"
 #include "llvm/IR/DerivedTypes.h"
 #include "llvm/IR/Function.h"
@@ -954,16 +953,16 @@
     ArgAttrVec.clear();
 
     Instruction *New = NewCS.getInstruction();
-    if (!Call->use_empty()) {
+    if (!Call->use_empty() || Call->isUsedByMetadata()) {
       if (New->getType() == Call->getType()) {
         // Return type not changed? Just replace users then.
         Call->replaceAllUsesWith(New);
         New->takeName(Call);
       } else if (New->getType()->isVoidTy()) {
-        // Our return value has uses, but they will get removed later on.
-        // Replace by null for now.
+        // If the return value is dead, replace any uses of it with undef
+        // (any non-debug value uses will get removed later on).
         if (!Call->getType()->isX86_MMXTy())
-          Call->replaceAllUsesWith(Constant::getNullValue(Call->getType()));
+          Call->replaceAllUsesWith(UndefValue::get(Call->getType()));
       } else {
         assert((RetTy->isStructTy() || RetTy->isArrayTy()) &&
                "Return type changed, but not into a void. The old return type"
@@ -1023,10 +1022,10 @@
       I2->takeName(&*I);
       ++I2;
     } else {
-      // If this argument is dead, replace any uses of it with null constants
-      // (these are guaranteed to become unused later on).
+      // If this argument is dead, replace any uses of it with undef
+      // (any non-debug value uses will get removed later on).
       if (!I->getType()->isX86_MMXTy())
-        I->replaceAllUsesWith(Constant::getNullValue(I->getType()));
+        I->replaceAllUsesWith(UndefValue::get(I->getType()));
     }
 
   // If we change the return value of the function we must rewrite any return
Index: llvm/trunk/test/Transforms/DeadArgElim/dbginfo-update-dbgval-local.ll
===================================================================
--- llvm/trunk/test/Transforms/DeadArgElim/dbginfo-update-dbgval-local.ll
+++ llvm/trunk/test/Transforms/DeadArgElim/dbginfo-update-dbgval-local.ll
@@ -0,0 +1,67 @@
+; RUN: opt -deadargelim -S < %s | FileCheck %s
+
+; Verify that the dbg.value intrinsics that use the dead argument and return
+; value are marked as undef to indicate that the values are optimized out.
+
+; Reproducer for PR23260.
+
+; CHECK-LABEL: define internal void @bar()
+; CHECK: call void @llvm.dbg.value(metadata i32 undef, metadata ![[LOCAL1:[0-9]+]]
+; CHECK: call void @sink()
+
+; Function Attrs: alwaysinline nounwind uwtable
+define internal i32 @bar(i32 %deadarg) #1 !dbg !10 {
+entry:
+  call void @llvm.dbg.value(metadata i32 %deadarg, metadata !15, metadata !DIExpression()), !dbg !17
+  call void @sink(), !dbg !17
+  ret i32 123, !dbg !17
+}
+
+; CHECK-LABEL: define void @foo()
+; CHECK: call void @bar()
+; CHECK: call void @llvm.dbg.value(metadata i32 undef, metadata ![[LOCAL2:[0-9]+]]
+; CHECK: call void @bar()
+
+; Function Attrs: nounwind uwtable
+define void @foo() #0 !dbg !6 {
+entry:
+  %deadret = call i32 @bar(i32 0), !dbg !9
+  call void @llvm.dbg.value(metadata i32 %deadret, metadata !16, metadata !DIExpression()), !dbg !9
+  call i32 @bar(i32 1), !dbg !9
+  ret void, !dbg !9
+}
+
+declare void @sink() local_unnamed_addr
+
+; Function Attrs: nounwind readnone speculatable
+declare void @llvm.dbg.value(metadata, metadata, metadata) #2
+
+attributes #0 = { nounwind uwtable }
+attributes #1 = { alwaysinline nounwind uwtable }
+attributes #2 = { nounwind readnone speculatable }
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4}
+!llvm.ident = !{!5}
+
+; CHECK: ![[LOCAL1]] = !DILocalVariable(name: "local1"
+; CHECK: ![[LOCAL2]] = !DILocalVariable(name: "local2"
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 8.0.0", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, nameTableKind: None)
+!1 = !DIFile(filename: "pr23260.c", directory: "/")
+!2 = !{}
+!3 = !{i32 2, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{!"clang version 8.0.0"}
+!6 = distinct !DISubprogram(name: "foo", scope: !1, file: !1, line: 3, type: !7, scopeLine: 3, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !2)
+!7 = !DISubroutineType(types: !8)
+!8 = !{null}
+!9 = !DILocation(line: 4, column: 3, scope: !6)
+!10 = distinct !DISubprogram(name: "bar", scope: !1, file: !1, line: 2, type: !11, scopeLine: 2, flags: DIFlagPrototyped, spFlags: DISPFlagLocalToUnit | DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !14)
+!11 = !DISubroutineType(types: !12)
+!12 = !{!13, !13}
+!13 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!14 = !{!15}
+!15 = !DILocalVariable(name: "local1", arg: 1, scope: !10, file: !1, line: 2, type: !13)
+!16 = !DILocalVariable(name: "local2", arg: 1, scope: !6, file: !1, line: 2, type: !13)
+!17 = !DILocation(line: 2, column: 52, scope: !10)