LLD: ELF: Simplify CreateELF.

[ruiu]

Summary

CreateELF was a combination of templates and C preprocessor macros.
This patch removes uses of macros.

Previously, we checked alignments based on the host environment.
It doesn't seem to make sense to me because we can use the linker
for cross compilation. So I relaxed the check in this patch.

[Bigcheese]

The alignment check is for the actual file location in memory. It has nothing to do with the target machine, only the machine running lld. However, because of archives, we always have to use an alignment of 2 anyway, so this patch is fine.

lib/ReaderWriter/ELF/CreateELF.h

 /// \param Traits
 /// Traits::create must be a template function which takes an ELFType and
 /// returns an ErrorOr<std::unique_ptr<lld::File>>.
 ///
 /// \param ident pair of EI_CLASS and EI_DATA.
 /// \param maxAlignment the maximum alignment of the file.
 /// \param args arguments forwarded to CreateELFTraits<T>::create.
 
-#define LLVM_CREATE_ELF_CreateELFTraits(endian, align, is64, ...) \
-  Traits::template create<ELFType<llvm::support::endian, align, is64>>( \
-      __VA_ARGS__);
-
-#if !LLVM_IS_UNALIGNED_ACCESS_FAST
-# define LLVM_CREATE_ELF_Create(normal, low, endian, is64, ...) \
-  if (maxAlignment >= normal) \
-    return LLVM_CREATE_ELF_CreateELFTraits(endian, normal, is64, __VA_ARGS__) \
-  else if (maxAlignment >= low) \
-    return LLVM_CREATE_ELF_CreateELFTraits(endian, low, is64, __VA_ARGS__) \
-  else \
-    llvm_unreachable("Invalid alignment for ELF file!");
-#else
-# define LLVM_CREATE_ELF_Create(normal, low, endian, is64, ...) \
-  if (maxAlignment >= low) \
-    return LLVM_CREATE_ELF_CreateELFTraits(endian, low, is64, __VA_ARGS__) \
-  else \
-    llvm_unreachable("Invalid alignment for ELF file!");
-#endif
-
 template <class Traits, class... Args>
 llvm::ErrorOr<std::unique_ptr<lld::File>>
 createELF(std::pair<unsigned char, unsigned char> ident,
           std::size_t maxAlignment, Args &&... args) {
-  if (ident.first == llvm::ELF::ELFCLASS32 &&
-      ident.second == llvm::ELF::ELFDATA2LSB) {
-    LLVM_CREATE_ELF_Create(4, 2, little, false, std::forward<Args>(args)...)
-  } else if (ident.first == llvm::ELF::ELFCLASS32 &&
-             ident.second == llvm::ELF::ELFDATA2MSB) {
-    LLVM_CREATE_ELF_Create(4, 2, big, false, std::forward<Args>(args)...)
-  } else if (ident.first == llvm::ELF::ELFCLASS64 &&
-             ident.second == llvm::ELF::ELFDATA2MSB) {
-    LLVM_CREATE_ELF_Create(8, 2, big, true, std::forward<Args>(args)...)
-  } else if (ident.first == llvm::ELF::ELFCLASS64 &&
-             ident.second == llvm::ELF::ELFDATA2LSB) {
-    LLVM_CREATE_ELF_Create(8, 2, little, true, std::forward<Args>(args)...)
+  using namespace llvm::ELF;
+  using namespace llvm::support;
+  unsigned char size = ident.first;
+  unsigned char endian = ident.second;
+
+  if (maxAlignment < 2)
+    llvm_unreachable("Invalid alignment for ELF file!");
+
+  if (size == ELFCLASS32 && endian == ELFDATA2LSB) {
+    return Traits::template create<ELFType<little, 2, false>>(
+        std::forward<Args>(args)...);
+  }
+  if (size == ELFCLASS32 && endian == ELFDATA2MSB) {
+    return Traits::template create<ELFType<big, 2, false>>(
+        std::forward<Args>(args)...);
+  }
+  if (size == ELFCLASS64 && endian == ELFDATA2LSB) {
+    return Traits::template create<ELFType<little, 2, true>>(
+        std::forward<Args>(args)...);
+  }
+  if (size == ELFCLASS64 && endian == ELFDATA2MSB) {
+    return Traits::template create<ELFType<big, 2, true>>(
+        std::forward<Args>(args)...);
   }
   llvm_unreachable("Invalid ELF type!");
 }
-} // end anon namespace
 
-#undef LLVM_CREATE_ELF_CreateELFTraits
-#undef LLVM_CREATE_ELF_Create
+} // end anon namespace
 
 #endif