RISCVAsmBackend: Simplify relaxDwarfLineAddr and remove getRelocPairForSize

Instead of creating two separate fixups, create a single one. Leverage
RISCVAsmBackend::addReloc to generate ADD/SUB relocation pairs.
In a future change MCFragment::setVarFixup may be restricted to a single
fixup.

Author: MaskRay

llvm/lib/Target/RISCV/MCTargetDesc/RISCVAsmBackend.cpp

@@ -331,15 +331,13 @@ bool RISCVAsmBackend::relaxDwarfLineAddr(MCFragment &F,
 
   int64_t LineDelta = F.getDwarfLineDelta();
   const MCExpr &AddrDelta = F.getDwarfAddrDelta();
-  SmallVector<MCFixup, 1> Fixups;
   size_t OldSize = F.getVarSize();
 
   int64_t Value;
   [[maybe_unused]] bool IsAbsolute =
       AddrDelta.evaluateKnownAbsolute(Value, *Asm);
   assert(IsAbsolute && "CFA with invalid expression");
 
-  Fixups.clear();
   SmallVector<char> Data;
   raw_svector_ostream OS(Data);
 
@@ -349,33 +347,23 @@ bool RISCVAsmBackend::relaxDwarfLineAddr(MCFragment &F,
     encodeSLEB128(LineDelta, OS);
   }
 
-  unsigned Offset;
-  std::pair<MCFixupKind, MCFixupKind> Fixup;
-
   // According to the DWARF specification, the `DW_LNS_fixed_advance_pc` opcode
   // takes a single unsigned half (unencoded) operand. The maximum encodable
   // value is therefore 65535.  Set a conservative upper bound for relaxation.
+  unsigned PCBytes;
   if (Value > 60000) {
     unsigned PtrSize = C.getAsmInfo()->getCodePointerSize();
-
-    OS << uint8_t(dwarf::DW_LNS_extended_op);
-    encodeULEB128(PtrSize + 1, OS);
-
-    OS << uint8_t(dwarf::DW_LNE_set_address);
-    Offset = OS.tell();
     assert((PtrSize == 4 || PtrSize == 8) && "Unexpected pointer size");
-    Fixup = RISCV::getRelocPairForSize(PtrSize);
+    PCBytes = PtrSize;
+    OS << uint8_t(dwarf::DW_LNS_extended_op) << uint8_t(PtrSize + 1)
+       << uint8_t(dwarf::DW_LNE_set_address);
     OS.write_zeros(PtrSize);
   } else {
+    PCBytes = 2;
     OS << uint8_t(dwarf::DW_LNS_fixed_advance_pc);
-    Offset = OS.tell();
-    Fixup = RISCV::getRelocPairForSize(2);
     support::endian::write<uint16_t>(OS, 0, llvm::endianness::little);
   }
-
-  const MCBinaryExpr &MBE = cast<MCBinaryExpr>(AddrDelta);
-  Fixups.push_back(MCFixup::create(Offset, MBE.getLHS(), std::get<0>(Fixup)));
-  Fixups.push_back(MCFixup::create(Offset, MBE.getRHS(), std::get<1>(Fixup)));
+  auto Offset = OS.tell() - PCBytes;
 
   if (LineDelta == INT64_MAX) {
     OS << uint8_t(dwarf::DW_LNS_extended_op);
@@ -386,7 +374,8 @@ bool RISCVAsmBackend::relaxDwarfLineAddr(MCFragment &F,
   }
 
   F.setVarContents(Data);
-  F.setVarFixups(Fixups);
+  F.setVarFixups({MCFixup::create(Offset, &AddrDelta,
+                                  MCFixup::getDataKindForSize(PCBytes))});
   WasRelaxed = OldSize != Data.size();
   return true;
 }

llvm/lib/Target/RISCV/MCTargetDesc/RISCVFixupKinds.h

@@ -68,27 +68,6 @@ enum Fixups {
   fixup_riscv_invalid,
   NumTargetFixupKinds = fixup_riscv_invalid - FirstTargetFixupKind
 };
-
-static inline std::pair<MCFixupKind, MCFixupKind>
-getRelocPairForSize(unsigned Size) {
-  switch (Size) {
-  default:
-    llvm_unreachable("unsupported fixup size");
-  case 1:
-    return std::make_pair(FirstLiteralRelocationKind + ELF::R_RISCV_ADD8,
-                          FirstLiteralRelocationKind + ELF::R_RISCV_SUB8);
-  case 2:
-    return std::make_pair(FirstLiteralRelocationKind + ELF::R_RISCV_ADD16,
-                          FirstLiteralRelocationKind + ELF::R_RISCV_SUB16);
-  case 4:
-    return std::make_pair(FirstLiteralRelocationKind + ELF::R_RISCV_ADD32,
-                          FirstLiteralRelocationKind + ELF::R_RISCV_SUB32);
-  case 8:
-    return std::make_pair(FirstLiteralRelocationKind + ELF::R_RISCV_ADD64,
-                          FirstLiteralRelocationKind + ELF::R_RISCV_SUB64);
-  }
-}
-
 } // end namespace llvm::RISCV
 
 #endif