Index: llvm/trunk/include/llvm/IR/DIBuilder.h
===================================================================
--- llvm/trunk/include/llvm/IR/DIBuilder.h
+++ llvm/trunk/include/llvm/IR/DIBuilder.h
@@ -108,12 +108,23 @@
     ///                 Objective-C.
     /// @param SplitName The name of the file that we'll split debug info out
     ///                  into.
+    /// @param Kind     The kind of debug information to generate.
+    /// @param EmitDebugInfo   A boolean flag which indicates whether debug
+    ///                        information should be written to the final
+    ///                        output or not. When this is false, debug
+    ///                        information annotations will be present in
+    ///                        the IL but they are not written to the final
+    ///                        assembly or object file. This supports tracking
+    ///                        source location information in the back end
+    ///                        without actually changing the output (e.g.,
+    ///                        when using optimization remarks).
     DICompileUnit createCompileUnit(unsigned Lang, StringRef File,
                                     StringRef Dir, StringRef Producer,
                                     bool isOptimized, StringRef Flags,
                                     unsigned RV,
                                     StringRef SplitName = StringRef(),
-                                    DebugEmissionKind Kind = FullDebug);
+                                    DebugEmissionKind Kind = FullDebug,
+                                    bool EmitDebugInfo = true);
 
     /// createFile - Create a file descriptor to hold debugging information
     /// for a file.
Index: llvm/trunk/lib/IR/DIBuilder.cpp
===================================================================
--- llvm/trunk/lib/IR/DIBuilder.cpp
+++ llvm/trunk/lib/IR/DIBuilder.cpp
@@ -102,7 +102,8 @@
                                            StringRef Producer, bool isOptimized,
                                            StringRef Flags, unsigned RunTimeVer,
                                            StringRef SplitName,
-                                           DebugEmissionKind Kind) {
+                                           DebugEmissionKind Kind,
+                                           bool EmitDebugInfo) {
 
   assert(((Lang <= dwarf::DW_LANG_OCaml && Lang >= dwarf::DW_LANG_C89) ||
           (Lang <= dwarf::DW_LANG_hi_user && Lang >= dwarf::DW_LANG_lo_user)) &&
@@ -140,8 +141,14 @@
   MDNode *CUNode = MDNode::get(VMContext, Elts);
 
   // Create a named metadata so that it is easier to find cu in a module.
-  NamedMDNode *NMD = M.getOrInsertNamedMetadata("llvm.dbg.cu");
-  NMD->addOperand(CUNode);
+  // Note that we only generate this when the caller wants to actually
+  // emit debug information. When we are only interested in tracking
+  // source line locations throughout the backend, we prevent codegen from
+  // emitting debug info in the final output by not generating llvm.dbg.cu.
+  if (EmitDebugInfo) {
+    NamedMDNode *NMD = M.getOrInsertNamedMetadata("llvm.dbg.cu");
+    NMD->addOperand(CUNode);
+  }
 
   return DICompileUnit(CUNode);
 }
Index: llvm/trunk/test/Transforms/LoopVectorize/X86/vectorization-remarks.ll
===================================================================
--- llvm/trunk/test/Transforms/LoopVectorize/X86/vectorization-remarks.ll
+++ llvm/trunk/test/Transforms/LoopVectorize/X86/vectorization-remarks.ll
@@ -1,6 +1,13 @@
 ; RUN: opt < %s -loop-vectorize -mtriple=x86_64-unknown-linux -S -pass-remarks='loop-vectorize' 2>&1 | FileCheck -check-prefix=VECTORIZED %s
 ; RUN: opt < %s -loop-vectorize -force-vector-width=1 -force-vector-unroll=4 -mtriple=x86_64-unknown-linux -S -pass-remarks='.*vectorize.*' 2>&1 | FileCheck -check-prefix=UNROLLED %s
 
+; This code has all the !dbg annotations needed to track source line information,
+; but is missing the llvm.dbg.cu annotation. This prevents code generation from
+; emitting debug info in the final output.
+; RUN: llc -mtriple x86_64-pc-linux-gnu %s -o - | FileCheck -check-prefix=DEBUG-OUTPUT %s
+; DEBUG-OUTPUT-NOT: .loc
+; DEBUG-OUTPUT-NOT: {{.*}}.debug_info
+
 ; VECTORIZED: remark: {{.*}}.c:17:8: vectorized loop (vectorization factor: 4, unrolling interleave factor: 1)
 ; UNROLLED: remark: {{.*}}.c:17:8: unrolled with interleaving factor 4 (vectorization not beneficial)
 
@@ -37,11 +44,9 @@
 
 declare void @ibar(i32*) #1
 
-!llvm.dbg.cu = !{!0}
 !llvm.module.flags = !{!7, !8}
 !llvm.ident = !{!9}
 
-!0 = metadata !{i32 786449, metadata !1, i32 12, metadata !"clang version 3.5.0 ", i1 true, metadata !"", i32 0, metadata !2, metadata !2, metadata !3, metadata !2, metadata !2, metadata !"", i32 2} ; [ DW_TAG_compile_unit ] [./vectorization-remarks.c] [DW_LANG_C99]
 !1 = metadata !{metadata !"vectorization-remarks.c", metadata !"."}
 !2 = metadata !{}
 !3 = metadata !{metadata !4}