[llvm] [DebugInfo][DWARF] Emit Per-Function Line Table Offsets and End Sequences (PR #110192)

[Zhaoxuan Jiang via llvm-commits]

================
@@ -2223,6 +2223,9 @@ void DwarfDebug::beginFunctionImpl(const MachineFunction *MF) {
     return;
 
   DwarfCompileUnit &CU = getOrCreateDwarfCompileUnit(SP->getUnit());
+  FunctionLineTableLabel = CU.emitFuncLineTableOffsets()
----------------
nocchijiang wrote:

After further investigation, I realized that this issue isn't strictly specific to Swift. Instead, it's related to scenarios where multiple CUs are emitted in one compiler invocation. In my case, the affected Swift module is configured with `-enable-single-module-llvm-emission`. 

The issue can be reproduced using tip-of-tree LLVM compiling llvm-test-suite with a slightly modified `ReleaseLTO-g.cmake` configuration (in order to enable `-emit-func-debug-line-table-offsets` for LTO objects).

```cmake
set(CMAKE_EXE_LINKER_FLAGS_RELEASE "-Wl,-mllvm,-emit-func-debug-line-table-offsets"  CACHE STRING "")
```

https://github.com/llvm/llvm-project/pull/110192