Update discriminator assignment algorithm in clang assembler.

Summary: The clang assembler assumes that the discriminator remains the same when there is source line change. The correct behavior is that when there is line change, discriminator will automatically reset to 0.

Reviewers: dnovillo, davidxl, echristo

Subscribers: echristo, llvm-commits

Differential Revision: http://reviews.llvm.org/D19436

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@267226 91177308-0d34-0410-b5e6-96231b3b80d8

Author: danielcdh

lib/MC/MCDwarf.cpp

@@ -112,6 +112,12 @@ EmitDwarfLineTable(MCObjectStreamer *MCOS, MCSection *Section,
             ie = LineEntries.end();
        it != ie; ++it) {
 
+    int64_t LineDelta = static_cast<int64_t>(it->getLine()) - LastLine;
+
+    // Discriminator will be cleared if there is line change.
+    if (LineDelta != 0)
+      Discriminator = 0;
+
     if (FileNum != it->getFileNum()) {
       FileNum = it->getFileNum();
       MCOS->EmitIntValue(dwarf::DW_LNS_set_file, 1);
@@ -146,7 +152,6 @@ EmitDwarfLineTable(MCObjectStreamer *MCOS, MCSection *Section,
     if (it->getFlags() & DWARF2_FLAG_EPILOGUE_BEGIN)
       MCOS->EmitIntValue(dwarf::DW_LNS_set_epilogue_begin, 1);
 
-    int64_t LineDelta = static_cast<int64_t>(it->getLine()) - LastLine;
     MCSymbol *Label = it->getLabel();
 
     // At this point we want to emit/create the sequence to encode the delta in