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

[Amir Ayupov via llvm-commits]

https://github.com/aaupov updated https://github.com/llvm/llvm-project/pull/89861

>From b6630e85ff5d4a35cf8d77fad63ba93791ffa806 Mon Sep 17 00:00:00 2001
From: Amir Ayupov <aaupov at fb.com>
Date: Tue, 23 Apr 2024 19:34:12 -0700
Subject: [PATCH 1/3] [Object] Provide operator< for ELFSymbolRef

Normally, operator< accepting DataRefImpl is used when comparing
SymbolRef/ELFSymbolRef. However, it uses std::memcmp which interprets
DataRefImpl union as char string. For ELFSymbolRef it's known that it
uses the struct view of the union, therefore a specialized operator< can
be used instead.
---
 llvm/include/llvm/Object/ELFObjectFile.h | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/llvm/include/llvm/Object/ELFObjectFile.h b/llvm/include/llvm/Object/ELFObjectFile.h
index 1d457be93741f2..8ec0e3fe15dc9d 100644
--- a/llvm/include/llvm/Object/ELFObjectFile.h
+++ b/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.b;
+}
+
 class elf_symbol_iterator : public symbol_iterator {
 public:
   elf_symbol_iterator(const basic_symbol_iterator &B)

>From f7e44cfd100904bfd1ea87312a1576f4f4c1524c Mon Sep 17 00:00:00 2001
From: Amir Ayupov <aaupov at fb.com>
Date: Wed, 24 Apr 2024 11:08:50 -0700
Subject: [PATCH 2/3] Use std::tie instead

---
 llvm/include/llvm/Object/ELFObjectFile.h | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/llvm/include/llvm/Object/ELFObjectFile.h b/llvm/include/llvm/Object/ELFObjectFile.h
index 8ec0e3fe15dc9d..11464f317ccd96 100644
--- a/llvm/include/llvm/Object/ELFObjectFile.h
+++ b/llvm/include/llvm/Object/ELFObjectFile.h
@@ -200,11 +200,8 @@ 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.b;
+  auto make_tie = [](DataRefImpl DRI) { return std::tie(DRI.d.a, DRI.d.b); };
+  return make_tie(A.getRawDataRefImpl()) < make_tie(B.getRawDataRefImpl());
 }
 
 class elf_symbol_iterator : public symbol_iterator {

>From 6e6905330cad0562b8a5e95f51b48f919cfffc39 Mon Sep 17 00:00:00 2001
From: Amir Ayupov <aaupov at fb.com>
Date: Wed, 24 Apr 2024 11:39:09 -0700
Subject: [PATCH 3/3] Add ELFObjectFileTest::ELFSymbolRefLess

---
 llvm/unittests/Object/ELFObjectFileTest.cpp | 36 +++++++++++++++++++++
 1 file changed, 36 insertions(+)

diff --git a/llvm/unittests/Object/ELFObjectFileTest.cpp b/llvm/unittests/Object/ELFObjectFileTest.cpp
index c4d2b4ae8b9acd..a4a0f6d4a7276d 100644
--- a/llvm/unittests/Object/ELFObjectFileTest.cpp
+++ b/llvm/unittests/Object/ELFObjectFileTest.cpp
@@ -1504,3 +1504,39 @@ 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;
+
+  llvm::object::DataRefImpl Data1;
+  Data1.d.a = 0x00000000;
+  Data1.d.b = 0x00000001;
+  SymbolRef Symbol1(Data1, &Obj);
+  ELFSymbolRef ELFSymbol1(Symbol1);
+
+  llvm::object::DataRefImpl Data2;
+  Data2.d.a = 0x00000000;
+  Data2.d.b = 0x00000100;
+  SymbolRef Symbol2(Data2, &Obj);
+  ELFSymbolRef ELFSymbol2(Symbol2);
+
+  // SymbolRef operator< uses std::memcmp treating the union as char string.
+  if (llvm::sys::IsLittleEndianHost)
+    EXPECT_FALSE(Symbol1 < Symbol2);
+  else
+    EXPECT_TRUE(Symbol1 < Symbol2);
+
+  // ELFSymbolRef operator< compares struct fields.
+  EXPECT_TRUE(ELFSymbol1 < ELFSymbol2);
+}