Fix dumping codeview line tables when there are multiple debug sections

Codeview line tables for functions in different sections refer to a common
STRING_TABLE_SUBSECTION for filenames.
This happens when building with -Gy or with inline functions with MSVC.

Original patch by Jeff Muizelaar!

llvm-svn: 219125
diff --git a/llvm/tools/llvm-readobj/COFFDumper.cpp b/llvm/tools/llvm-readobj/COFFDumper.cpp
index 53fba14..8e7fcc0 100644
--- a/llvm/tools/llvm-readobj/COFFDumper.cpp
+++ b/llvm/tools/llvm-readobj/COFFDumper.cpp
@@ -82,6 +82,8 @@
 
   const llvm::object::COFFObjectFile *Obj;
   RelocMapTy RelocMap;
+  StringRef CVFileIndexToStringOffsetTable;
+  StringRef CVStringTable;
 };
 
 } // namespace
@@ -440,8 +442,6 @@
 
   SmallVector<StringRef, 10> FunctionNames;
   StringMap<StringRef> FunctionLineTables;
-  StringRef FileIndexToStringOffsetTable;
-  StringRef StringTable;
 
   ListScope D(W, "CodeViewLineTables");
   {
@@ -502,25 +502,25 @@
         break;
       }
       case COFF::DEBUG_STRING_TABLE_SUBSECTION:
-        if (PayloadSize == 0 || StringTable.data() != nullptr ||
+        if (PayloadSize == 0 || CVStringTable.data() != nullptr ||
             Contents.back() != '\0') {
           // Empty or duplicate or non-null-terminated subsection.
           error(object_error::parse_failed);
           return;
         }
-        StringTable = Contents;
+        CVStringTable = Contents;
         break;
       case COFF::DEBUG_INDEX_SUBSECTION:
         // Holds the translation table from file indices
         // to offsets in the string table.
 
         if (PayloadSize == 0 ||
-            FileIndexToStringOffsetTable.data() != nullptr) {
+            CVFileIndexToStringOffsetTable.data() != nullptr) {
           // Empty or duplicate subsection.
           error(object_error::parse_failed);
           return;
         }
-        FileIndexToStringOffsetTable = Contents;
+        CVFileIndexToStringOffsetTable = Contents;
         break;
       }
       Offset += PayloadSize;
@@ -555,7 +555,7 @@
 
       uint32_t FilenameOffset;
       {
-        DataExtractor SDE(FileIndexToStringOffsetTable, true, 4);
+        DataExtractor SDE(CVFileIndexToStringOffsetTable, true, 4);
         uint32_t OffsetInSDE = OffsetInIndex;
         if (!SDE.isValidOffset(OffsetInSDE)) {
           error(object_error::parse_failed);
@@ -564,15 +564,15 @@
         FilenameOffset = SDE.getU32(&OffsetInSDE);
       }
 
-      if (FilenameOffset == 0 || FilenameOffset + 1 >= StringTable.size() ||
-          StringTable.data()[FilenameOffset - 1] != '\0') {
+      if (FilenameOffset == 0 || FilenameOffset + 1 >= CVStringTable.size() ||
+          CVStringTable.data()[FilenameOffset - 1] != '\0') {
         // Each string in an F3 subsection should be preceded by a null
         // character.
         error(object_error::parse_failed);
         return;
       }
 
-      StringRef Filename(StringTable.data() + FilenameOffset);
+      StringRef Filename(CVStringTable.data() + FilenameOffset);
       ListScope S(W, "FilenameSegment");
       W.printString("Filename", Filename);
       for (unsigned J = 0; J != SegmentLength && DE.isValidOffset(Offset);