Index: include/clang/AST/Expr.h
===================================================================
--- include/clang/AST/Expr.h
+++ include/clang/AST/Expr.h
@@ -1611,7 +1611,10 @@
   ///
   SourceLocation getLocationOfByte(unsigned ByteNo, const SourceManager &SM,
                                    const LangOptions &Features,
-                                   const TargetInfo &Target) const;
+                                   const TargetInfo &Target,
+                                   unsigned * StartToken=nullptr,
+                                   unsigned * ByteOffset=nullptr
+                                   ) const;

   typedef const SourceLocation *tokloc_iterator;
   tokloc_iterator tokloc_begin() const { return TokLocs; }
Index: lib/AST/Expr.cpp
===================================================================
--- lib/AST/Expr.cpp
+++ lib/AST/Expr.cpp
@@ -1009,13 +1009,19 @@
 ///
 SourceLocation StringLiteral::
 getLocationOfByte(unsigned ByteNo, const SourceManager &SM,
-                  const LangOptions &Features, const TargetInfo &Target) const {
+                  const LangOptions &Features, const TargetInfo &Target,
+                  unsigned * StartToken, unsigned * ByteOffset) const {
   assert((Kind == StringLiteral::Ascii || Kind == StringLiteral::UTF8) &&
          "Only narrow string literals are currently supported");

   // Loop over all of the tokens in this string until we find the one that
   // contains the byte we're looking for.
   unsigned TokNo = 0;
+  unsigned StringOffset = 0;
+  if (StartToken)
+    TokNo = *StartToken;
+  if (ByteOffset)
+    StringOffset = *ByteOffset;
   while (1) {
     assert(TokNo < getNumConcatenated() && "Invalid byte number!");
     SourceLocation StrTokLoc = getStrTokenLoc(TokNo);
@@ -1029,8 +1035,13 @@
     std::pair<FileID, unsigned> LocInfo =SM.getDecomposedLoc(StrTokSpellingLoc);
     bool Invalid = false;
     StringRef Buffer = SM.getBufferData(LocInfo.first, &Invalid);
-    if (Invalid)
+    if (Invalid) {
+      if (ByteOffset != nullptr)
+        *ByteOffset = StringOffset;
+      if (StartToken != nullptr)
+        *StartToken = TokNo;
       return StrTokSpellingLoc;
+    }

     const char *StrData = Buffer.data()+LocInfo.second;

@@ -1051,10 +1062,15 @@
       
       // Now that we know the offset of the token in the spelling, use the
       // preprocessor to get the offset in the original source.
+      if (ByteOffset != nullptr)
+        *ByteOffset = StringOffset;
+      if (StartToken != nullptr)
+        *StartToken = TokNo;
       return Lexer::AdvanceToTokenCharacter(StrTokLoc, Offset, SM, Features);
     }
     
     // Move to the next string token.
+    StringOffset += TokNumBytes;
     ++TokNo;
     ByteNo -= TokNumBytes;
   }
Index: lib/CodeGen/CGStmt.cpp
===================================================================
--- lib/CodeGen/CGStmt.cpp
+++ lib/CodeGen/CGStmt.cpp
@@ -1707,13 +1707,18 @@
   if (!StrVal.empty()) {
     const SourceManager &SM = CGF.CGM.getContext().getSourceManager();
     const LangOptions &LangOpts = CGF.CGM.getLangOpts();
+    unsigned StartToken = 0;
+    unsigned ByteOffset = 0;
 
     // Add the location of the start of each subsequent line of the asm to the
     // MDNode.
     for (unsigned i = 0, e = StrVal.size()-1; i != e; ++i) {
       if (StrVal[i] != '\n') continue;
-      SourceLocation LineLoc = Str->getLocationOfByte(i+1, SM, LangOpts,
-                                                      CGF.getTarget());
+      SourceLocation LineLoc = Str->getLocationOfByte(i+1-ByteOffset, SM,
+                                                      LangOpts,
+                                                      CGF.getTarget(),
+                                                      &StartToken,
+                                                      &ByteOffset);
       Locs.push_back(llvm::ConstantAsMetadata::get(
           llvm::ConstantInt::get(CGF.Int32Ty, LineLoc.getRawEncoding())));
     }