Restructure DwarfDebug::beginInstruction (NFC).

[probinson]

Summary

Based on discussion in D24180, redo the method with less indentation which should help make the other patch easier to understand.

[dblaikie]

lib/CodeGen/AsmPrinter/DwarfDebug.cpp

1016–1037

Would it help to reverse these two and early return from the UnknownLocations case - so the major "if (DL)" case could be non-indented? (but if the way you've got it works best for your other patch, that's cool)

[probinson]

lib/CodeGen/AsmPrinter/DwarfDebug.cpp

1016–1037

Yes, thanks, it does help a bit. That one is still the biggest case, even with the other patch.

lib/CodeGen/AsmPrinter/DwarfDebug.cpp

 }
 
 // Process beginning of an instruction.
 void DwarfDebug::beginInstruction(const MachineInstr *MI) {
   DebugHandlerBase::beginInstruction(MI);
   assert(CurMI);
 
   // Check if source location changes, but ignore DBG_VALUE locations.
-  if (!MI->isDebugValue()) {
-    const DebugLoc &DL = MI->getDebugLoc();
-    if (DL != PrevInstLoc) {
-      if (DL) {
-        unsigned Flags = 0;
-        PrevInstLoc = DL;
-        if (DL == PrologEndLoc) {
-          Flags |= DWARF2_FLAG_PROLOGUE_END;
-          PrologEndLoc = DebugLoc();
-          Flags |= DWARF2_FLAG_IS_STMT;
-        }
-        if (DL.getLine() !=
-            Asm->OutStreamer->getContext().getCurrentDwarfLoc().getLine())
-          Flags |= DWARF2_FLAG_IS_STMT;
+  if (MI->isDebugValue())
+    return;
+  if (DL == PrevInstLoc)
+    return;
+
+    // We have a new, explicit location.
 
-        const MDNode *Scope = DL.getScope();
-        recordSourceLine(DL.getLine(), DL.getCol(), Scope, Flags);
-      } else if (UnknownLocations) {
-        PrevInstLoc = DL;
-        recordSourceLine(0, 0, nullptr, 0);
-      }
-    }
-  }
-}
+    return;
+  }
+  // We have an unspecified location.
+  if (UnknownLocations) {
 
 static DebugLoc findPrologueEndLoc(const MachineFunction *MF) {
   // First known non-DBG_VALUE and non-frame setup location marks
   // the beginning of the function body.
   for (const auto &MBB : *MF)
     for (const auto &MI : MBB)
       if (!MI.isDebugValue() && !MI.getFlag(MachineInstr::FrameSetup) &&
           MI.getDebugLoc())