Index: llvm/trunk/bindings/go/llvm/dibuilder.go
===================================================================
--- llvm/trunk/bindings/go/llvm/dibuilder.go
+++ llvm/trunk/bindings/go/llvm/dibuilder.go
@@ -54,6 +54,7 @@
 	FlagVector
 	FlagStaticMember
 	FlagIndirectVariable
+	FlagArgumentNotModified
 )
 
 type DwarfLang uint32
Index: llvm/trunk/docs/LangRef.rst
===================================================================
--- llvm/trunk/docs/LangRef.rst
+++ llvm/trunk/docs/LangRef.rst
@@ -4764,6 +4764,18 @@
     !4 = !DIExpression(DW_OP_constu, 2, DW_OP_swap, DW_OP_xderef)
     !5 = !DIExpression(DW_OP_constu, 42, DW_OP_stack_value)
 
+DIFlags
+"""""""""""""""
+
+These flags encode various properties of DINodes.
+
+The `ArgumentNotModified` flag marks a function argument whose value
+is not modified throughout of a function. This flag is used to decide
+whether a DW_OP_entry_value can be used in a location description
+after the function prologue. The language frontend is expected to compute
+this property for each DILocalVariable. The flag should be used
+only in optimized code.
+
 DIObjCProperty
 """"""""""""""
 
Index: llvm/trunk/include/llvm/IR/DebugInfoFlags.def
===================================================================
--- llvm/trunk/include/llvm/IR/DebugInfoFlags.def
+++ llvm/trunk/include/llvm/IR/DebugInfoFlags.def
@@ -50,6 +50,7 @@
 HANDLE_DI_FLAG((1 << 18), IntroducedVirtual)
 HANDLE_DI_FLAG((1 << 19), BitField)
 HANDLE_DI_FLAG((1 << 20), NoReturn)
+HANDLE_DI_FLAG((1 << 21), ArgumentNotModified)
 HANDLE_DI_FLAG((1 << 22), TypePassByValue)
 HANDLE_DI_FLAG((1 << 23), TypePassByReference)
 HANDLE_DI_FLAG((1 << 24), EnumClass)
Index: llvm/trunk/include/llvm/IR/DebugInfoMetadata.h
===================================================================
--- llvm/trunk/include/llvm/IR/DebugInfoMetadata.h
+++ llvm/trunk/include/llvm/IR/DebugInfoMetadata.h
@@ -2796,6 +2796,11 @@
   bool isArtificial() const { return getFlags() & FlagArtificial; }
   bool isObjectPointer() const { return getFlags() & FlagObjectPointer; }
 
+  /// Check that an argument is unmodified.
+  bool isNotModified() const { return getFlags() & FlagArgumentNotModified; }
+  /// Set the flag if an argument is unmodified.
+  void setIsNotModified() { Flags |= FlagArgumentNotModified; }
+
   /// Check that a location is valid for this variable.
   ///
   /// Check that \c DL exists, is in the same subprogram, and has the same
Index: llvm/trunk/test/Assembler/debug-info.ll
===================================================================
--- llvm/trunk/test/Assembler/debug-info.ll
+++ llvm/trunk/test/Assembler/debug-info.ll
@@ -1,8 +1,8 @@
 ; RUN: llvm-as < %s | llvm-dis | llvm-as | llvm-dis | FileCheck %s
 ; RUN: verify-uselistorder %s
 
-; CHECK: !named = !{!0, !0, !1, !2, !3, !4, !5, !6, !7, !8, !8, !9, !10, !11, !12, !13, !14, !15, !16, !17, !18, !19, !20, !21, !22, !23, !24, !25, !26, !27, !27, !28, !29, !30, !31, !32, !33, !34, !35, !36, !37, !38, !39}
-!named = !{!0, !1, !2, !3, !4, !5, !6, !7, !8, !9, !10, !11, !12, !13, !14, !15, !16, !17, !18, !19, !20, !21, !22, !23, !24, !25, !26, !27, !28, !29, !30, !31, !32, !33, !34, !35, !36, !37, !38, !39, !40, !41, !42}
+; CHECK: !named = !{!0, !0, !1, !2, !3, !4, !5, !6, !7, !8, !8, !9, !10, !11, !12, !13, !14, !15, !16, !17, !18, !19, !20, !21, !22, !23, !24, !25, !26, !27, !27, !28, !29, !30, !31, !32, !33, !34, !35, !36, !37, !38, !39, !40, !41}
+!named = !{!0, !1, !2, !3, !4, !5, !6, !7, !8, !9, !10, !11, !12, !13, !14, !15, !16, !17, !18, !19, !20, !21, !22, !23, !24, !25, !26, !27, !28, !29, !30, !31, !32, !33, !34, !35, !36, !37, !38, !39, !40, !41, !42, !43, !44}
 
 ; CHECK:      !0 = !DISubrange(count: 3)
 ; CHECK-NEXT: !1 = !DISubrange(count: 3, lowerBound: 4)
@@ -99,3 +99,8 @@
 ; CHECK-NEXT: !39 = !DIBasicType(name: "u64.le", size: 64, align: 1, encoding: DW_ATE_unsigned, flags: DIFlagLittleEndian)
 !41 = !DIBasicType(name: "u64.be", size: 64, align: 1, encoding: DW_ATE_unsigned, flags: DIFlagBigEndian)
 !42 = !DIBasicType(name: "u64.le", size: 64, align: 1, encoding: DW_ATE_unsigned, flags: DIFlagLittleEndian)
+
+; CHECK-NEXT: !40 = distinct !DISubprogram(name: "fn", scope: {{.*}}, file: {{.*}}, spFlags: 0)
+; CHECK-NEXT: !41 = !DILocalVariable(name: "Name", arg: 1, scope: {{.*}}, file: {{.*}}, line: 13, type: {{.*}}, flags: DIFlagArgumentNotModified)
+!43 = distinct !DISubprogram(name: "fn", scope: !12, file: !12, spFlags: 0)
+!44 = !DILocalVariable(name: "Name", arg: 1, scope: !43, file: !12, line: 13, type: !7, flags: DIFlagArgumentNotModified)