[clang] [llvm] [dwarf] make dwarf fission compatible with RISCV relaxations (PR #164128)

[David Blaikie via llvm-commits]

================
@@ -3290,34 +3275,70 @@ static MCSymbol *emitLoclistsTableHeader(AsmPrinter *Asm,
   return TableEnd;
 }
 
-template <typename Ranges, typename PayloadEmitter>
-static void emitRangeList(
-    DwarfDebug &DD, AsmPrinter *Asm, MCSymbol *Sym, const Ranges &R,
-    const DwarfCompileUnit &CU, unsigned BaseAddressx, unsigned OffsetPair,
-    unsigned StartxLength, unsigned EndOfList,
-    StringRef (*StringifyEnum)(unsigned),
-    bool ShouldUseBaseAddress,
-    PayloadEmitter EmitPayload) {
+namespace {
+
+struct DebugLocSpanList {
+  MCSymbol *Label;
+  const DwarfCompileUnit *CU;
+  llvm::ArrayRef<llvm::DebugLocStream::Entry> Ranges;
+};
+
+template <typename DWARFSpanList> struct DwarfRangeListTraits {};
+
+template <> struct DwarfRangeListTraits<DebugLocSpanList> {
+  static constexpr unsigned BaseAddressx = dwarf::DW_LLE_base_addressx;
+  static constexpr unsigned OffsetPair = dwarf::DW_LLE_offset_pair;
+  static constexpr unsigned StartxLength = dwarf::DW_LLE_startx_length;
+  static constexpr unsigned StartxEndx = dwarf::DW_LLE_startx_endx;
+  static constexpr unsigned EndOfList = dwarf::DW_LLE_end_of_list;
+
+  static StringRef StringifyRangeKind(unsigned Encoding) {
+    return llvm::dwarf::LocListEncodingString(Encoding);
+  }
+};
+
+template <> struct DwarfRangeListTraits<RangeSpanList> {
+  static constexpr unsigned BaseAddressx = dwarf::DW_RLE_base_addressx;
+  static constexpr unsigned OffsetPair = dwarf::DW_RLE_offset_pair;
+  static constexpr unsigned StartxLength = dwarf::DW_RLE_startx_length;
+  static constexpr unsigned StartxEndx = dwarf::DW_RLE_startx_endx;
+  static constexpr unsigned EndOfList = dwarf::DW_RLE_end_of_list;
+
+  static StringRef StringifyRangeKind(unsigned Encoding) {
+    return llvm::dwarf::RangeListEncodingString(Encoding);
+  }
+};
+
+} // namespace
+
+template <
+    typename Ranges, typename PayloadEmitter,
+    std::enable_if_t<DwarfRangeListTraits<Ranges>::BaseAddressx, bool> = true>
----------------
dwblaikie wrote:

Probably doesn't need the enable_if SFINAE? (emitRangeList isn't overloaded, right? So it can just fail to compile if someone passes in a range that doesn't have matching traits?)

& could you split this change out - do the trait-based change as NFC (but still send it for review) then do the relaxation stuff on top of that, would help isolate the changes?

https://github.com/llvm/llvm-project/pull/164128