Index: lib/Transforms/Scalar/SampleProfile.cpp
===================================================================
--- lib/Transforms/Scalar/SampleProfile.cpp
+++ lib/Transforms/Scalar/SampleProfile.cpp
@@ -630,6 +630,30 @@
   }
 }
 
+/// \brief Locate the DISubprogram for F.
+///
+/// We look for the first instruction that has a debug annotation
+/// leading back to \p F.
+///
+/// \returns a valid DISubprogram if found. Otherwise, it returns an empty
+/// DISubprogram.
+static const DISubprogram getDISubprogram(Function &F, const LLVMContext &Ctx) {
+  for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I) {
+    BasicBlock *B = I;
+    for (BasicBlock::iterator BI = B->begin(), BE = B->end(); BI != BE; ++BI) {
+      Instruction &Inst = *BI;
+      DebugLoc DLoc = Inst.getDebugLoc();
+      if (!DLoc.isUnknown()) {
+        const MDNode *Scope = DLoc.getScopeNode(Ctx);
+        DISubprogram Subprogram = getDISubprogram(Scope);
+        return Subprogram.describes(&F) ? Subprogram : DISubprogram();
+      }
+    }
+  }
+
+  return DISubprogram();
+}
+
 /// \brief Get the line number for the function header.
 ///
 /// This looks up function \p F in the current compilation unit and
@@ -642,21 +666,16 @@
 /// \returns the line number where \p F is defined. If it returns 0,
 ///          it means that there is no debug information available for \p F.
 unsigned SampleProfileLoader::getFunctionLoc(Function &F) {
-  NamedMDNode *CUNodes = F.getParent()->getNamedMetadata("llvm.dbg.cu");
-  if (CUNodes) {
-    for (unsigned I = 0, E1 = CUNodes->getNumOperands(); I != E1; ++I) {
-      DICompileUnit CU(CUNodes->getOperand(I));
-      DIArray Subprograms = CU.getSubprograms();
-      for (unsigned J = 0, E2 = Subprograms.getNumElements(); J != E2; ++J) {
-        DISubprogram Subprogram(Subprograms.getElement(J));
-        if (Subprogram.describes(&F))
-          return Subprogram.getLineNumber();
-      }
-    }
-  }
+  const DISubprogram &S = getDISubprogram(F, *Ctx);
+  if (S.isSubprogram())
+    return S.getLineNumber();
 
+  // If could not find the start of \p F, emit a diagnostic to warn the user
+  // about the missed opportunity.
   F.getContext().diagnose(DiagnosticInfoSampleProfile(
-      "No debug information found in function " + F.getName()));
+      "No debug information found in function " + F.getName() +
+          ": Function profile not used",
+      DS_Warning));
   return 0;
 }
 
Index: test/Transforms/SampleProfile/calls.ll
===================================================================
--- test/Transforms/SampleProfile/calls.ll
+++ test/Transforms/SampleProfile/calls.ll
@@ -15,7 +15,12 @@
 ;   printf("sum is %d\n", s);
 ;   return 0;
 ; }
-
+;
+; Note that this test is missing the llvm.dbg.cu annotation. This emulates
+; the effect of the user having only used -fprofile-sample-use without
+; -gmlt when invoking the driver. In those cases, we need to track source
+; location information but we do not have to generate debug info in the
+; final binary.
 @.str = private unnamed_addr constant [11 x i8] c"sum is %d\0A\00", align 1
 
 ; Function Attrs: nounwind uwtable
@@ -84,7 +89,6 @@
 
 declare i32 @printf(i8*, ...) #2
 
-!llvm.dbg.cu = !{!0}
 !llvm.module.flags = !{!8, !9}
 !llvm.ident = !{!10}
 
Index: test/Transforms/SampleProfile/syntax.ll
===================================================================
--- test/Transforms/SampleProfile/syntax.ll
+++ test/Transforms/SampleProfile/syntax.ll
@@ -1,4 +1,4 @@
-; RUN: not opt < %s -sample-profile -sample-profile-file=%S/Inputs/syntax.prof 2>&1 | FileCheck -check-prefix=NO-DEBUG %s
+; RUN: opt < %s -sample-profile -sample-profile-file=%S/Inputs/syntax.prof 2>&1 | FileCheck -check-prefix=NO-DEBUG %s
 ; RUN: not opt < %s -sample-profile -sample-profile-file=missing.prof 2>&1 | FileCheck -check-prefix=MISSING-FILE %s
 ; RUN: not opt < %s -sample-profile -sample-profile-file=%S/Inputs/bad_fn_header.prof 2>&1 | FileCheck -check-prefix=BAD-FN-HEADER %s
 ; RUN: not opt < %s -sample-profile -sample-profile-file=%S/Inputs/bad_sample_line.prof 2>&1 | FileCheck -check-prefix=BAD-SAMPLE-LINE %s
@@ -11,7 +11,7 @@
 entry:
   ret void
 }
-; NO-DEBUG: error: No debug information found in function empty
+; NO-DEBUG: warning: No debug information found in function empty: Function profile not used
 ; MISSING-FILE: error: missing.prof:
 ; BAD-FN-HEADER: error: {{.*}}bad_fn_header.prof:1: Expected 'mangled_name:NUM:NUM', found 3empty:100:BAD
 ; BAD-SAMPLE-LINE: error: {{.*}}bad_sample_line.prof:3: Expected 'NUM[.NUM]: NUM[ mangled_name:NUM]*', found 1: BAD