[llvm] [MC] Add .loc_label instruction (PR #99710)

[Fangrui Song via llvm-commits]

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@@ -243,17 +256,36 @@ void MCDwarfLineTable::emitOne(
     Discriminator = 0;
     LastLine = LineEntry.getLine();
     LastLabel = Label;
+    IsAtStartSeq = false;
   }
 
   // Generate DWARF line end entry.
   // We do not need this for DwarfDebug that explicitly terminates the line
   // table using ranges whenever CU or section changes. However, the MC path
   // does not track ranges nor terminate the line table. In that case,
   // conservatively use the section end symbol to end the line table.
-  if (!EndEntryEmitted)
+  if (!EndEntryEmitted && !IsAtStartSeq)
     MCOS->emitDwarfLineEndEntry(Section, LastLabel);
 }
 
+void MCDwarfLineTable::endCurrentSeqAndEmitLineStreamLabel(MCStreamer *MCOS,
+                                                           SMLoc DefLoc,
+                                                           StringRef Name) {
+  auto &ctx = MCOS->getContext();
+  auto *LineStreamLabel = ctx.getOrCreateSymbol(Name);
+  auto *LineSym = ctx.createTempSymbol();
+  MCOS->emitLabel(LineSym);
+  const MCDwarfLoc &DwarfLoc = ctx.getCurrentDwarfLoc();
+
+  // Create a 'fake' line entry by having LineStreamLabel be non-null. This
+  // won't actually emit any line information, it will reset the line table
+  // sequence and emit a label at the start of the new line table sequence.
+  MCDwarfLineEntry LineEntry(LineSym, DwarfLoc, LineStreamLabel, DefLoc);
+
+  // Add the line entry to this section's entries.
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MaskRay wrote:

Delete the comment. self-explaining code doesn't need a comment. 

https://github.com/llvm/llvm-project/pull/99710