[llvm] [DWARF] Emit line 0 source locations for BB padding nops (PR #99496)

[Paul T Robinson via llvm-commits]

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@@ -3668,3 +3668,19 @@ bool DwarfDebug::alwaysUseRanges(const DwarfCompileUnit &CU) const {
     return true;
   return false;
 }
+
+void DwarfDebug::beginCodeAlignment(const MachineBasicBlock &MBB) {
+  auto *SP = MBB.getParent()->getFunction().getSubprogram();
+
+  bool NoDebug =
+      !SP || SP->getUnit()->getEmissionKind() == DICompileUnit::NoDebug;
+
+  if (NoDebug)
+    return;
+
+  auto PrevLoc = Asm->OutStreamer->getContext().getCurrentDwarfLoc();
+  Asm->OutStreamer->emitDwarfLocDirective(
+      PrevLoc.getFileNum(), 0, PrevLoc.getColumn(), 0, 0, 0, StringRef());
+  MCDwarfLineEntry::make(Asm->OutStreamer.get(),
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pogo59 wrote:

OK, so because in this case we're looking at a .align directive rather than a real instruction, it won't be passing through `emitInstructionImpl()` so we need to call `MCDwarfLineEntry::make()` directly. Sounds reasonable.

https://github.com/llvm/llvm-project/pull/99496