[Object] Provide operator< for ELFSymbolRef (#89861)

Normally, operator< accepting DataRefImpl is used when comparing
SymbolRef/ELFSymbolRef. However, it uses std::memcmp which interprets
DataRefImpl union as char string so that the result depends on host
endianness.
For ELFSymbolRef a specialized operator< can be used instead to produce
consistent ordering regardless of endianness by comparing the symbol
table index and symbol index fields separately.

llvm/include/llvm/Object/ELFObjectFile.h

@@ -199,6 +199,14 @@ class ELFSymbolRef : public SymbolRef {
   }
 };
 
+inline bool operator<(const ELFSymbolRef &A, const ELFSymbolRef &B) {
+  const DataRefImpl &DRIA = A.getRawDataRefImpl();
+  const DataRefImpl &DRIB = B.getRawDataRefImpl();
+  if (DRIA.d.a == DRIB.d.a)
+    return DRIA.d.b < DRIB.d.b;
+  return DRIA.d.a < DRIB.d.a;
+}
+
 class elf_symbol_iterator : public symbol_iterator {
 public:
   elf_symbol_iterator(const basic_symbol_iterator &B)

llvm/unittests/Object/ELFObjectFileTest.cpp

@@ -1504,3 +1504,46 @@ TEST(ELFObjectFileTest, GetSectionAndRelocations) {
                "SHT_RELA section with index 1: failed to get a "
                "relocated section: invalid section index: 255");
 }
+
+TEST(ELFObjectFileTest, ELFSymbolRefLess) {
+  SmallString<0> Storage;
+  Expected<ELFObjectFile<ELF64LE>> ElfOrErr = toBinary<ELF64LE>(Storage, R"(
+--- !ELF
+FileHeader:
+  Class:   ELFCLASS64
+  Data:    ELFDATA2LSB
+  Type:    ET_DYN
+  Machine: EM_X86_64
+)");
+
+  ASSERT_THAT_EXPECTED(ElfOrErr, Succeeded());
+  const ELFObjectFile<ELF64LE> &Obj = *ElfOrErr;
+
+  const uint32_t ValLow = 0x00000001;
+  const uint32_t ValHigh = 0x00000100;
+
+  auto MakeSymbol = [&Obj](size_t SymtabIndex, size_t SymbolIndex) {
+    DataRefImpl Data;
+    Data.d.a = SymtabIndex;
+    Data.d.b = SymbolIndex;
+    SymbolRef Sym(Data, &Obj);
+    return ELFSymbolRef(Sym);
+  };
+
+  ELFSymbolRef ELFSymLowLow = MakeSymbol(ValLow, ValLow);
+  ELFSymbolRef ELFSymLowHigh = MakeSymbol(ValLow, ValHigh);
+  ELFSymbolRef ELFSymHighLow = MakeSymbol(ValHigh, ValLow);
+  ELFSymbolRef ELFSymHighHigh = MakeSymbol(ValHigh, ValHigh);
+
+  EXPECT_TRUE(ELFSymLowLow < ELFSymLowHigh);
+  EXPECT_FALSE(ELFSymLowHigh < ELFSymLowLow);
+  EXPECT_FALSE(ELFSymLowLow < ELFSymLowLow);
+
+  EXPECT_TRUE(ELFSymLowLow < ELFSymHighHigh);
+  EXPECT_TRUE(ELFSymLowHigh < ELFSymHighLow);
+  EXPECT_TRUE(ELFSymLowLow < ELFSymHighLow);
+
+  EXPECT_FALSE(ELFSymHighLow < ELFSymLowHigh);
+  EXPECT_FALSE(ELFSymHighHigh < ELFSymLowLow);
+  EXPECT_FALSE(ELFSymHighLow < ELFSymLowLow);
+}