Index: lib/CodeGen/IRBuilder.cpp
===================================================================
--- lib/CodeGen/IRBuilder.cpp
+++ lib/CodeGen/IRBuilder.cpp
@@ -34,7 +34,10 @@
                      Value *arg1 = nullptr) {
   MDNode *ID;
   SmallVector<Value *, 3> Args;
-  Args.push_back(nullptr);
+  // Use a temporary node to safely create a unique pointer for the first arg.
+  MDNode *TempNode = MDNode::getTemporary(Ctx, None);
+  // Reserve operand 0 for loop id self reference.
+  Args.push_back(TempNode);
 
   if (arg0)
     Args.push_back(arg0);
@@ -43,6 +46,7 @@
 
   ID = MDNode::get(Ctx, Args);
   ID->replaceOperandWith(0, ID);
+  MDNode::deleteTemporary(TempNode);
   return ID;
 }
 
Index: test/Isl/CodeGen/LoopParallelMD/do_not_mutate_debug_info.ll
===================================================================
--- /dev/null
+++ test/Isl/CodeGen/LoopParallelMD/do_not_mutate_debug_info.ll
@@ -0,0 +1,71 @@
+; This test checks that we do not accidently mutate the debug info when
+; inserting loop parallel metadata.
+; RUN: opt %loadPolly < %s  -S -polly -polly-codegen-isl -polly-ast-detect-parallel | FileCheck %s
+; CHECK-NOT: !7 = metadata !{metadata !7}
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+@A = common global i32* null, align 8
+
+; Function Attrs: nounwind uwtable
+define void @foo() {
+entry:
+  tail call void @llvm.dbg.value(metadata !18, i64 0, metadata !9, metadata !19), !dbg !20
+  %0 = load i32** @A, align 8, !dbg !21, !tbaa !23
+  br label %for.body, !dbg !27
+
+for.body:                                         ; preds = %for.body, %entry
+  %indvars.iv = phi i64 [ 0, %entry ], [ %indvars.iv.next, %for.body ]
+  %arrayidx = getelementptr inbounds i32* %0, i64 %indvars.iv, !dbg !21
+  %1 = load i32* %arrayidx, align 4, !dbg !21, !tbaa !30
+  %add = add nsw i32 %1, 1, !dbg !21
+  store i32 %add, i32* %arrayidx, align 4, !dbg !21, !tbaa !30
+  %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1, !dbg !27
+  %exitcond = icmp eq i64 %indvars.iv, 1, !dbg !27
+  br i1 %exitcond, label %for.end, label %for.body, !dbg !27
+
+for.end:                                          ; preds = %for.body
+  ret void, !dbg !32
+}
+
+; Function Attrs: nounwind readnone
+declare void @llvm.dbg.value(metadata, i64, metadata, metadata)
+
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!15, !16}
+!llvm.ident = !{!17}
+
+!0 = metadata !{metadata !"0x11\0012\00clang version 3.6.0 \001\00\000\00\001", metadata !1, metadata !2, metadata !2, metadata !3, metadata !12, metadata !2} ; [ DW_TAG_compile_unit ] [/local/mnt/workspace/build/tip-Release/t2.c] [DW_LANG_C99]
+!1 = metadata !{metadata !"t2.c", metadata !"/local/mnt/workspace/build/tip-Release"}
+!2 = metadata !{}
+!3 = metadata !{metadata !4}
+!4 = metadata !{metadata !"0x2e\00foo\00foo\00\003\000\001\000\000\000\001\003", metadata !1, metadata !5, metadata !6, null, void ()* @foo, null, null, metadata !8} ; [ DW_TAG_subprogram ] [line 3] [def] [foo]
+!5 = metadata !{metadata !"0x29", metadata !1}    ; [ DW_TAG_file_type ] [/local/mnt/workspace/build/tip-Release/t2.c]
+!6 = metadata !{metadata !"0x15\00\000\000\000\000\000\000", null, null, null, metadata !7, null, null, null} ; [ DW_TAG_subroutine_type ] [line 0, size 0, align 0, offset 0] [from ]
+!7 = metadata !{null}
+!8 = metadata !{metadata !9}
+!9 = metadata !{metadata !"0x100\00i\004\000", metadata !10, metadata !5, metadata !11} ; [ DW_TAG_auto_variable ] [i] [line 4]
+!10 = metadata !{metadata !"0xb\004\003\000", metadata !1, metadata !4} ; [ DW_TAG_lexical_block ] [/local/mnt/workspace/build/tip-Release/t2.c]
+!11 = metadata !{metadata !"0x24\00int\000\0032\0032\000\000\005", null, null} ; [ DW_TAG_base_type ] [int] [line 0, size 32, align 32, offset 0, enc DW_ATE_signed]
+!12 = metadata !{metadata !13}
+!13 = metadata !{metadata !"0x34\00A\00A\00\002\000\001", null, metadata !5, metadata !14, i32** @A, null} ; [ DW_TAG_variable ] [A] [line 2] [def]
+!14 = metadata !{metadata !"0xf\00\000\0064\0064\000\000", null, null, metadata !11} ; [ DW_TAG_pointer_type ] [line 0, size 64, align 64, offset 0] [from int]
+!15 = metadata !{i32 2, metadata !"Dwarf Version", i32 4}
+!16 = metadata !{i32 2, metadata !"Debug Info Version", i32 2}
+!17 = metadata !{metadata !"clang version 3.6.0 "}
+!18 = metadata !{i32 0}
+!19 = metadata !{metadata !"0x102"}               ; [ DW_TAG_expression ]
+!20 = metadata !{i32 4, i32 12, metadata !10, null}
+!21 = metadata !{i32 5, i32 5, metadata !22, null}
+!22 = metadata !{metadata !"0xb\004\003\001", metadata !1, metadata !10} ; [ DW_TAG_lexical_block ] [/local/mnt/workspace/build/tip-Release/t2.c]
+!23 = metadata !{metadata !24, metadata !24, i64 0}
+!24 = metadata !{metadata !"any pointer", metadata !25, i64 0}
+!25 = metadata !{metadata !"omnipotent char", metadata !26, i64 0}
+!26 = metadata !{metadata !"Simple C/C++ TBAA"}
+!27 = metadata !{i32 4, i32 3, metadata !28, null}
+!28 = metadata !{metadata !"0xb\002", metadata !1, metadata !29} ; [ DW_TAG_lexical_block ] [/local/mnt/workspace/build/tip-Release/t2.c]
+!29 = metadata !{metadata !"0xb\001", metadata !1, metadata !22} ; [ DW_TAG_lexical_block ] [/local/mnt/workspace/build/tip-Release/t2.c]
+!30 = metadata !{metadata !31, metadata !31, i64 0}
+!31 = metadata !{metadata !"int", metadata !25, i64 0}
+!32 = metadata !{i32 6, i32 1, metadata !4, null}