Index: lib/CodeGen/PeepholeOptimizer.cpp
===================================================================
--- lib/CodeGen/PeepholeOptimizer.cpp
+++ lib/CodeGen/PeepholeOptimizer.cpp
@@ -505,12 +505,13 @@
     return false;
 
   unsigned Reg = MI->getOperand(0).getReg();
-  // To reduce compilation time, we check MRI->hasOneUse when inserting
+  // To reduce compilation time, we check MRI->hasOneNonDBGUse when inserting
   // loads. It should be checked when processing uses of the load, since
   // uses can be removed during peephole.
   if (!MI->getOperand(0).getSubReg() &&
       TargetRegisterInfo::isVirtualRegister(Reg) &&
-      MRI->hasOneUse(Reg)) {
+      // Only count NonDBG uses.
+      MRI->hasOneNonDBGUse(Reg)) {
     FoldAsLoadDefReg = Reg;
     return true;
   }
@@ -594,10 +595,14 @@
       ++MII;
       LocalMIs.insert(MI);
 
+      // Skip debug values. They should not effect this peephole optimization.
+      if (MI->isDebugValue())
+          continue;
+
       // If there exists an instruction which belongs to the following
       // categories, we will discard the load candidate.
       if (MI->isLabel() || MI->isPHI() || MI->isImplicitDef() ||
-          MI->isKill() || MI->isInlineAsm() || MI->isDebugValue() ||
+          MI->isKill() || MI->isInlineAsm() ||
           MI->hasUnmodeledSideEffects()) {
         FoldAsLoadDefReg = 0;
         continue;
@@ -633,6 +638,7 @@
       if (!isLoadFoldable(MI, FoldAsLoadDefReg) && FoldAsLoadDefReg) {
         // We need to fold load after optimizeCmpInstr, since optimizeCmpInstr
         // can enable folding by converting SUB to CMP.
+        unsigned FoldedReg = FoldAsLoadDefReg; // Need this below
         MachineInstr *DefMI = 0;
         MachineInstr *FoldMI = TII->optimizeLoadInstr(MI, MRI,
                                                       FoldAsLoadDefReg, DefMI);
@@ -649,6 +655,18 @@
 
           // MI is replaced with FoldMI.
           Changed = true;
+
+          // Mark any DBG_VALUE that uses FoldReg as undef (but don't 
+          // delete it.)  Code copied from DeadMachineInstructionElim.
+          MachineRegisterInfo::use_iterator nextI;
+          for (MachineRegisterInfo::use_iterator I = MRI->use_begin(FoldedReg),
+               E = MRI->use_end(); I!=E; I=nextI) {
+            nextI = llvm::next(I);  // I is invalidated by the setReg
+            MachineOperand& Use = I.getOperand();
+            MachineInstr *UseMI = Use.getParent();
+            if (UseMI->isDebugValue())
+                UseMI->getOperand(0).setReg(0U);
+          }
           continue;
         }
       }
Index: test/CodeGen/X86/dbg-changes-codegen-1.ll
===================================================================
--- test/CodeGen/X86/dbg-changes-codegen-1.ll
+++ test/CodeGen/X86/dbg-changes-codegen-1.ll
@@ -0,0 +1,83 @@
+; RUN: llc < %s -march=x86-64 | FileCheck %s
+
+; The Peephole optimizer should fold the load into the cmp even with debug info.
+; CHECK-NOT: cmpq {{%[a-z]+}}, {{%[a-z]+}}
+; CHECK: cmpq {{%[a-z]+}}, wibble(%rip)
+
+; The following bitcode was generated with:
+;   clang -emit-llvm -S -O2 -g
+; from this source:
+;   struct Foo {
+;     bool bar();
+;     bool operator==(Foo &baz) { return (this == &baz); }
+;   };
+;   Foo *wibble;
+;   bool Foo::bar() { return (*this == *wibble); }
+
+%struct.Foo = type { i8 }
+
+@wibble = global %struct.Foo* null, align 8
+
+; Function Attrs: nounwind readonly uwtable
+define zeroext i1 @_ZN3Foo3barEv(%struct.Foo* readnone %this) #0 align 2 {
+entry:
+  tail call void @llvm.dbg.value(metadata !{%struct.Foo* %this}, i64 0, metadata !20), !dbg !32
+  %0 = load %struct.Foo** @wibble, align 8, !dbg !33, !tbaa !34
+  tail call void @llvm.dbg.value(metadata !{%struct.Foo* %this}, i64 0, metadata !38), !dbg !39
+  tail call void @llvm.dbg.value(metadata !{%struct.Foo* %0}, i64 0, metadata !40), !dbg !41
+  %cmp.i = icmp eq %struct.Foo* %0, %this, !dbg !41
+  ret i1 %cmp.i, !dbg !33
+}
+
+; Function Attrs: nounwind readnone
+declare void @llvm.dbg.value(metadata, i64, metadata) #1
+
+attributes #0 = { nounwind readonly uwtable "less-precise-fpmad"="false" "no-frame-pointer-elim"="false" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #1 = { nounwind readnone }
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!29, !30}
+!llvm.ident = !{!31}
+
+!0 = metadata !{i32 786449, metadata !1, i32 4, metadata !"clang version 3.5 (trunk 201298)", i1 true, metadata !"", i32 0, metadata !2, metadata !3, metadata !17, metadata !27, metadata !2, metadata !""} ; [ DW_TAG_compile_unit ] [/home/kromanova/test1.cpp] [DW_LANG_C_plus_plus]
+!1 = metadata !{metadata !"test1.cpp", metadata !"/home/kromanova"}
+!2 = metadata !{}
+!3 = metadata !{metadata !4}
+!4 = metadata !{i32 786451, metadata !1, null, metadata !"Foo", i32 1, i64 8, i64 8, i32 0, i32 0, null, metadata !5, i32 0, null, null, metadata !"_ZTS3Foo"} ; [ DW_TAG_structure_type ] [Foo] [line 1, size 8, align 8, offset 0] [def] [from ]
+!5 = metadata !{metadata !6, metadata !12}
+!6 = metadata !{i32 786478, metadata !1, metadata !"_ZTS3Foo", metadata !"bar", metadata !"bar", metadata !"_ZN3Foo3barEv", i32 2, metadata !7, i1 false, i1 false, i32 0, i32 0, null, i32 256, i1 true, null, null, i32 0, metadata !11, i32 2} ; [ DW_TAG_subprogram ] [line 2] [bar]
+!7 = metadata !{i32 786453, i32 0, null, metadata !"", i32 0, i64 0, i64 0, i64 0, i32 0, null, metadata !8, i32 0, null, null, null} ; [ DW_TAG_subroutine_type ] [line 0, size 0, align 0, offset 0] [from ]
+!8 = metadata !{metadata !9, metadata !10}
+!9 = metadata !{i32 786468, null, null, metadata !"bool", i32 0, i64 8, i64 8, i64 0, i32 0, i32 2} ; [ DW_TAG_base_type ] [bool] [line 0, size 8, align 8, offset 0, enc DW_ATE_boolean]
+!10 = metadata !{i32 786447, null, null, metadata !"", i32 0, i64 64, i64 64, i64 0, i32 1088, metadata !"_ZTS3Foo"} ; [ DW_TAG_pointer_type ] [line 0, size 64, align 64, offset 0] [artificial] [from _ZTS3Foo]
+!11 = metadata !{i32 786468}
+!12 = metadata !{i32 786478, metadata !1, metadata !"_ZTS3Foo", metadata !"operator==", metadata !"operator==", metadata !"_ZN3FooeqERS_", i32 3, metadata !13, i1 false, i1 false, i32 0, i32 0, null, i32 256, i1 true, null, null, i32 0, metadata !16, i32 3} ; [ DW_TAG_subprogram ] [line 3] [operator==]
+!13 = metadata !{i32 786453, i32 0, null, metadata !"", i32 0, i64 0, i64 0, i64 0, i32 0, null, metadata !14, i32 0, null, null, null} ; [ DW_TAG_subroutine_type ] [line 0, size 0, align 0, offset 0] [from ]
+!14 = metadata !{metadata !9, metadata !10, metadata !15}
+!15 = metadata !{i32 786448, null, null, null, i32 0, i64 0, i64 0, i64 0, i32 0, metadata !"_ZTS3Foo"} ; [ DW_TAG_reference_type ] [line 0, size 0, align 0, offset 0] [from _ZTS3Foo]
+!16 = metadata !{i32 786468}
+!17 = metadata !{metadata !18, metadata !22}
+!18 = metadata !{i32 786478, metadata !1, metadata !"_ZTS3Foo", metadata !"bar", metadata !"bar", metadata !"_ZN3Foo3barEv", i32 6, metadata !7, i1 false, i1 true, i32 0, i32 0, null, i32 256, i1 true, i1 (%struct.Foo*)* @_ZN3Foo3barEv, null, metadata !6, metadata !19, i32 6} ; [ DW_TAG_subprogram ] [line 6] [def] [bar]
+!19 = metadata !{metadata !20}
+!20 = metadata !{i32 786689, metadata !18, metadata !"this", null, i32 16777216, metadata !21, i32 1088, i32 0} ; [ DW_TAG_arg_variable ] [this] [line 0]
+!21 = metadata !{i32 786447, null, null, metadata !"", i32 0, i64 64, i64 64, i64 0, i32 0, metadata !"_ZTS3Foo"} ; [ DW_TAG_pointer_type ] [line 0, size 64, align 64, offset 0] [from _ZTS3Foo]
+!22 = metadata !{i32 786478, metadata !1, metadata !"_ZTS3Foo", metadata !"operator==", metadata !"operator==", metadata !"_ZN3FooeqERS_", i32 3, metadata !13, i1 false, i1 true, i32 0, i32 0, null, i32 256, i1 true, null, null, metadata !12, metadata !23, i32 3} ; [ DW_TAG_subprogram ] [line 3] [def] [operator==]
+!23 = metadata !{metadata !24, metadata !25}
+!24 = metadata !{i32 786689, metadata !22, metadata !"this", null, i32 16777216, metadata !21, i32 1088, i32 0} ; [ DW_TAG_arg_variable ] [this] [line 0]
+!25 = metadata !{i32 786689, metadata !22, metadata !"baz", metadata !26, i32 33554435, metadata !15, i32 0, i32 0} ; [ DW_TAG_arg_variable ] [baz] [line 3]
+!26 = metadata !{i32 786473, metadata !1}         ; [ DW_TAG_file_type ] [/home/kromanova/test1.cpp]
+!27 = metadata !{metadata !28}
+!28 = metadata !{i32 786484, i32 0, null, metadata !"wibble", metadata !"wibble", metadata !"", metadata !26, i32 5, metadata !21, i32 0, i32 1, %struct.Foo** @wibble, null} ; [ DW_TAG_variable ] [wibble] [line 5] [def]
+!29 = metadata !{i32 2, metadata !"Dwarf Version", i32 4}
+!30 = metadata !{i32 1, metadata !"Debug Info Version", i32 1}
+!31 = metadata !{metadata !"clang version 3.5 (trunk 201298)"}
+!32 = metadata !{i32 0, i32 0, metadata !18, null}
+!33 = metadata !{i32 6, i32 0, metadata !18, null}
+!34 = metadata !{metadata !35, metadata !35, i64 0}
+!35 = metadata !{metadata !"any pointer", metadata !36, i64 0}
+!36 = metadata !{metadata !"omnipotent char", metadata !37, i64 0}
+!37 = metadata !{metadata !"Simple C/C++ TBAA"}
+!38 = metadata !{i32 786689, metadata !22, metadata !"this", null, i32 16777216, metadata !21, i32 1088, metadata !33} ; [ DW_TAG_arg_variable ] [this] [line 0]
+!39 = metadata !{i32 0, i32 0, metadata !22, metadata !33}
+!40 = metadata !{i32 786689, metadata !22, metadata !"baz", metadata !26, i32 33554435, metadata !15, i32 0, metadata !33} ; [ DW_TAG_arg_variable ] [baz] [line 3]
+!41 = metadata !{i32 3, i32 0, metadata !22, metadata !33}
Index: test/CodeGen/X86/dbg-changes-codegen-2.ll
===================================================================
--- test/CodeGen/X86/dbg-changes-codegen-2.ll
+++ test/CodeGen/X86/dbg-changes-codegen-2.ll
@@ -0,0 +1,109 @@
+; RUN: llc < %s -march=x86-64 | FileCheck %s
+
+; The Peephole optimizer should fold the load into the cmp even with debug info.
+; CHECK-NOT: cmpq {{%[a-z]+}}, {{%[a-z]+}}
+; CHECK: cmpq {{%[a-z]+}}, b(%rip)
+
+; The following bitcode was generated with:
+;   clang -emit-llvm -S -O2 -g
+; from this source:
+;   struct Wibble {
+;     int x;
+;   } *a, *b;
+;   struct Flibble {
+;     void bar(Wibble *c) {
+;       if (c < b)
+;         b = 0;
+;       c->x = 0;
+;     }
+;   } f;
+;   void baz() { f.bar(a); }
+
+
+%struct.Wibble = type { i32 }
+%struct.Flibble = type { i8 }
+
+@a = global %struct.Wibble* null, align 8
+@b = global %struct.Wibble* null, align 8
+@f = global %struct.Flibble zeroinitializer, align 1
+
+; Function Attrs: nounwind uwtable
+define void @_Z3bazv() #0 {
+entry:
+  %0 = load %struct.Wibble** @a, align 8, !dbg !33, !tbaa !34
+  tail call void @llvm.dbg.value(metadata !38, i64 0, metadata !39), !dbg !40
+  tail call void @llvm.dbg.value(metadata !{%struct.Wibble* %0}, i64 0, metadata !41), !dbg !42
+  %1 = load %struct.Wibble** @b, align 8, !dbg !43, !tbaa !34
+  %cmp.i = icmp ugt %struct.Wibble* %1, %0, !dbg !43
+  br i1 %cmp.i, label %if.then.i, label %_ZN7Flibble3barEP6Wibble.exit, !dbg !43
+
+if.then.i:                                        ; preds = %entry
+  store %struct.Wibble* null, %struct.Wibble** @b, align 8, !dbg !45, !tbaa !34
+  br label %_ZN7Flibble3barEP6Wibble.exit, !dbg !45
+
+_ZN7Flibble3barEP6Wibble.exit:                    ; preds = %entry, %if.then.i
+  %x.i = getelementptr inbounds %struct.Wibble* %0, i64 0, i32 0, !dbg !46
+  store i32 0, i32* %x.i, align 4, !dbg !46, !tbaa !47
+  ret void, !dbg !33
+}
+
+; Function Attrs: nounwind readnone
+declare void @llvm.dbg.value(metadata, i64, metadata) #1
+
+attributes #0 = { nounwind uwtable "less-precise-fpmad"="false" "no-frame-pointer-elim"="false" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #1 = { nounwind readnone }
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!30, !31}
+!llvm.ident = !{!32}
+
+!0 = metadata !{i32 786449, metadata !1, i32 4, metadata !"clang version 3.5 (trunk 201298)", i1 true, metadata !"", i32 0, metadata !2, metadata !3, metadata !16, metadata !26, metadata !2, metadata !""} ; [ DW_TAG_compile_unit ] [/home/kromanova/test2.cpp] [DW_LANG_C_plus_plus]
+!1 = metadata !{metadata !"test2.cpp", metadata !"/home/kromanova"}
+!2 = metadata !{}
+!3 = metadata !{metadata !4, metadata !8}
+!4 = metadata !{i32 786451, metadata !1, null, metadata !"Wibble", i32 1, i64 32, i64 32, i32 0, i32 0, null, metadata !5, i32 0, null, null, metadata !"_ZTS6Wibble"} ; [ DW_TAG_structure_type ] [Wibble] [line 1, size 32, align 32, offset 0] [def] [from ]
+!5 = metadata !{metadata !6}
+!6 = metadata !{i32 786445, metadata !1, metadata !"_ZTS6Wibble", metadata !"x", i32 2, i64 32, i64 32, i64 0, i32 0, metadata !7} ; [ DW_TAG_member ] [x] [line 2, size 32, align 32, offset 0] [from int]
+!7 = metadata !{i32 786468, null, null, metadata !"int", i32 0, i64 32, i64 32, i64 0, i32 0, i32 5} ; [ DW_TAG_base_type ] [int] [line 0, size 32, align 32, offset 0, enc DW_ATE_signed]
+!8 = metadata !{i32 786451, metadata !1, null, metadata !"Flibble", i32 4, i64 8, i64 8, i32 0, i32 0, null, metadata !9, i32 0, null, null, metadata !"_ZTS7Flibble"} ; [ DW_TAG_structure_type ] [Flibble] [line 4, size 8, align 8, offset 0] [def] [from ]
+!9 = metadata !{metadata !10}
+!10 = metadata !{i32 786478, metadata !1, metadata !"_ZTS7Flibble", metadata !"bar", metadata !"bar", metadata !"_ZN7Flibble3barEP6Wibble", i32 5, metadata !11, i1 false, i1 false, i32 0, i32 0, null, i32 256, i1 true, null, null, i32 0, metadata !15, i32 5} ; [ DW_TAG_subprogram ] [line 5] [bar]
+!11 = metadata !{i32 786453, i32 0, null, metadata !"", i32 0, i64 0, i64 0, i64 0, i32 0, null, metadata !12, i32 0, null, null, null} ; [ DW_TAG_subroutine_type ] [line 0, size 0, align 0, offset 0] [from ]
+!12 = metadata !{null, metadata !13, metadata !14}
+!13 = metadata !{i32 786447, null, null, metadata !"", i32 0, i64 64, i64 64, i64 0, i32 1088, metadata !"_ZTS7Flibble"} ; [ DW_TAG_pointer_type ] [line 0, size 64, align 64, offset 0] [artificial] [from _ZTS7Flibble]
+!14 = metadata !{i32 786447, null, null, metadata !"", i32 0, i64 64, i64 64, i64 0, i32 0, metadata !"_ZTS6Wibble"} ; [ DW_TAG_pointer_type ] [line 0, size 64, align 64, offset 0] [from _ZTS6Wibble]
+!15 = metadata !{i32 786468}
+!16 = metadata !{metadata !17, metadata !21}
+!17 = metadata !{i32 786478, metadata !1, metadata !18, metadata !"baz", metadata !"baz", metadata !"_Z3bazv", i32 11, metadata !19, i1 false, i1 true, i32 0, i32 0, null, i32 256, i1 true, void ()* @_Z3bazv, null, null, metadata !2, i32 11} ; [ DW_TAG_subprogram ] [line 11] [def] [baz]
+!18 = metadata !{i32 786473, metadata !1}         ; [ DW_TAG_file_type ] [/home/kromanova/test2.cpp]
+!19 = metadata !{i32 786453, i32 0, null, metadata !"", i32 0, i64 0, i64 0, i64 0, i32 0, null, metadata !20, i32 0, null, null, null} ; [ DW_TAG_subroutine_type ] [line 0, size 0, align 0, offset 0] [from ]
+!20 = metadata !{null}
+!21 = metadata !{i32 786478, metadata !1, metadata !"_ZTS7Flibble", metadata !"bar", metadata !"bar", metadata !"_ZN7Flibble3barEP6Wibble", i32 5, metadata !11, i1 false, i1 true, i32 0, i32 0, null, i32 256, i1 true, null, null, metadata !10, metadata !22, i32 5} ; [ DW_TAG_subprogram ] [line 5] [def] [bar]
+!22 = metadata !{metadata !23, metadata !25}
+!23 = metadata !{i32 786689, metadata !21, metadata !"this", null, i32 16777216, metadata !24, i32 1088, i32 0} ; [ DW_TAG_arg_variable ] [this] [line 0]
+!24 = metadata !{i32 786447, null, null, metadata !"", i32 0, i64 64, i64 64, i64 0, i32 0, metadata !"_ZTS7Flibble"} ; [ DW_TAG_pointer_type ] [line 0, size 64, align 64, offset 0] [from _ZTS7Flibble]
+!25 = metadata !{i32 786689, metadata !21, metadata !"c", metadata !18, i32 33554437, metadata !14, i32 0, i32 0} ; [ DW_TAG_arg_variable ] [c] [line 5]
+!26 = metadata !{metadata !27, metadata !28, metadata !29}
+!27 = metadata !{i32 786484, i32 0, null, metadata !"a", metadata !"a", metadata !"", metadata !18, i32 3, metadata !14, i32 0, i32 1, %struct.Wibble** @a, null} ; [ DW_TAG_variable ] [a] [line 3] [def]
+!28 = metadata !{i32 786484, i32 0, null, metadata !"b", metadata !"b", metadata !"", metadata !18, i32 3, metadata !14, i32 0, i32 1, %struct.Wibble** @b, null} ; [ DW_TAG_variable ] [b] [line 3] [def]
+!29 = metadata !{i32 786484, i32 0, null, metadata !"f", metadata !"f", metadata !"", metadata !18, i32 10, metadata !8, i32 0, i32 1, %struct.Flibble* @f, null} ; [ DW_TAG_variable ] [f] [line 10] [def]
+!30 = metadata !{i32 2, metadata !"Dwarf Version", i32 4}
+!31 = metadata !{i32 1, metadata !"Debug Info Version", i32 1}
+!32 = metadata !{metadata !"clang version 3.5 (trunk 201298)"}
+!33 = metadata !{i32 11, i32 0, metadata !17, null}
+!34 = metadata !{metadata !35, metadata !35, i64 0}
+!35 = metadata !{metadata !"any pointer", metadata !36, i64 0}
+!36 = metadata !{metadata !"omnipotent char", metadata !37, i64 0}
+!37 = metadata !{metadata !"Simple C/C++ TBAA"}
+!38 = metadata !{%struct.Flibble* @f}
+!39 = metadata !{i32 786689, metadata !21, metadata !"this", null, i32 16777216, metadata !24, i32 1088, metadata !33} ; [ DW_TAG_arg_variable ] [this] [line 0]
+!40 = metadata !{i32 0, i32 0, metadata !21, metadata !33}
+!41 = metadata !{i32 786689, metadata !21, metadata !"c", metadata !18, i32 33554437, metadata !14, i32 0, metadata !33} ; [ DW_TAG_arg_variable ] [c] [line 5]
+!42 = metadata !{i32 5, i32 0, metadata !21, metadata !33}
+!43 = metadata !{i32 6, i32 0, metadata !44, metadata !33}
+!44 = metadata !{i32 786443, metadata !1, metadata !21, i32 6, i32 0, i32 0} ; [ DW_TAG_lexical_block ] [/home/kromanova/test2.cpp]
+!45 = metadata !{i32 7, i32 0, metadata !44, metadata !33}
+!46 = metadata !{i32 8, i32 0, metadata !21, metadata !33} ; [ DW_TAG_imported_declaration ]
+!47 = metadata !{metadata !48, metadata !49, i64 0}
+!48 = metadata !{metadata !"_ZTS6Wibble", metadata !49, i64 0}
+!49 = metadata !{metadata !"int", metadata !36, i64 0}