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Author: daniilavdeev

llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp

@@ -3372,6 +3372,12 @@ emitRangeList(DwarfDebug &DD, AsmPrinter *Asm, MCSymbol *Sym, const Ranges &R,
           Asm->emitLabelDifference(End, Base, Size);
         }
       } else if (UseDwarf5) {
+        // NOTE: We can't use absoluteSymbolDiff here instead of
+        // isRangeRelaxable. While isRangeRelaxable only checks that the offset
+        // between labels won't change at link time (which is exactly what we
+        // need), absoluteSymbolDiff also requires that the offset remain
+        // unchanged at assembly time, imposing a much stricter condition.
+        // Consequently, this would lead to less optimal debug info emission.
         if (DD.useSplitDwarf() && llvm::isRangeRelaxable(Begin, End)) {
           Asm->OutStreamer->AddComment(StringifyEnum(StartxEndx));
           Asm->emitInt8(StartxEndx);

llvm/lib/MC/MCSymbol.cpp

@@ -87,6 +87,10 @@ void MCSymbol::print(raw_ostream &OS, const MCAsmInfo *MAI) const {
 LLVM_DUMP_METHOD void MCSymbol::dump() const { dbgs() << *this; }
 #endif
 
+// Determine whether the offset between two labels can change at link time.
+// Currently, this function is used only in DWARF info emission logic, where it
+// helps generate more optimal debug info when the offset between labels is
+// constant at link time.
 bool llvm::isRangeRelaxable(const MCSymbol *Begin, const MCSymbol *End) {
   assert(Begin && "Range without a begin symbol?");
   assert(End && "Range without an end symbol?");