[llvm] [nfc][InstrProf]Remove 'offsetOf' when parsing indexed profiles (PR #93346)

[Kazu Hirata via llvm-commits]

================
@@ -1627,66 +1627,46 @@ void OverlapStats::dump(raw_fd_ostream &OS) const {
 }
 
 namespace IndexedInstrProf {
-// A C++14 compatible version of the offsetof macro.
-template <typename T1, typename T2>
-inline size_t constexpr offsetOf(T1 T2::*Member) {
-  constexpr T2 Object{};
-  return size_t(&(Object.*Member)) - size_t(&Object);
-}
-
-// Read a uint64_t from the specified buffer offset, and swap the bytes in
-// native endianness if necessary.
-static inline uint64_t read(const unsigned char *Buffer, size_t Offset) {
-  using namespace ::support;
-  return endian::read<uint64_t, llvm::endianness::little, unaligned>(Buffer +
-                                                                     Offset);
-}
-
 Expected<Header> Header::readFromBuffer(const unsigned char *Buffer) {
   using namespace support;
   static_assert(std::is_standard_layout_v<Header>,
-                "The header should be standard layout type since we use offset "
-                "of fields to read.");
+                "Use standard layout for Header for simplicity");
   Header H;
 
-  H.Magic = read(Buffer, offsetOf(&Header::Magic));
+  H.Magic =
+      endian::readNext<uint64_t, llvm::endianness::little, unaligned>(Buffer);
   // Check the magic number.
   if (H.Magic != IndexedInstrProf::Magic)
     return make_error<InstrProfError>(instrprof_error::bad_magic);
 
   // Read the version.
-  H.Version = read(Buffer, offsetOf(&Header::Version));
+  H.Version =
+      endian::readNext<uint64_t, llvm::endianness::little, unaligned>(Buffer);
   if (H.getIndexedProfileVersion() >
       IndexedInstrProf::ProfVersion::CurrentVersion)
     return make_error<InstrProfError>(instrprof_error::unsupported_version);
 
-  switch (H.getIndexedProfileVersion()) {
-    // When a new field is added in the header add a case statement here to
-    // populate it.
-    static_assert(
-        IndexedInstrProf::ProfVersion::CurrentVersion == Version12,
-        "Please update the reading code below if a new field has been added, "
-        "if not add a case statement to fall through to the latest version.");
-  case 12ull:
-    H.VTableNamesOffset = read(Buffer, offsetOf(&Header::VTableNamesOffset));
-    [[fallthrough]];
-  case 11ull:
-    [[fallthrough]];
-  case 10ull:
+  static_assert(IndexedInstrProf::ProfVersion::CurrentVersion == Version12,
+                "Please update the reading as needed when a new field is added "
----------------
kazutakahirata wrote:

```suggestion
                "Please update the reader as needed when a new field is added "
```

https://github.com/llvm/llvm-project/pull/93346