From d9d2f187759d0154574657c195068d367c338473 Mon Sep 17 00:00:00 2001
From: "Michael J. Spencer" <bigcheesegs@gmail.com>
Date: Sun, 3 Feb 2013 10:48:31 +0000
Subject: [PATCH] [Support] Add LLVM_IS_UNALIGNED_ACCESS_FAST.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@174271 91177308-0d34-0410-b5e6-96231b3b80d8
---
 include/llvm/Support/Compiler.h | 13 +++++++++++++
 lib/Object/ELFObjectFile.cpp    | 20 ++++++++++++++++----
 2 files changed, 29 insertions(+), 4 deletions(-)

diff --git a/include/llvm/Support/Compiler.h b/include/llvm/Support/Compiler.h
index 36539f6d346..6ca86bdd502 100644
--- a/include/llvm/Support/Compiler.h
+++ b/include/llvm/Support/Compiler.h
@@ -311,4 +311,17 @@
 # define LLVM_MEMORY_SANITIZER_BUILD 0
 #endif
 
+/// \macro LLVM_IS_UNALIGNED_ACCESS_FAST
+/// \brief Is unaligned memory access fast on the host machine.
+///
+/// Don't specialize on alignment for platforms where unaligned memory accesses
+/// generates the same code as aligned memory accesses for common types.
+#if defined(_M_AMD64) || defined(_M_IX86) || defined(__amd64) || \
+    defined(__amd64__) || defined(__x86_64) || defined(__x86_64__) || \
+    defined(_X86_) || defined(__i386) || defined(__i386__)
+# define LLVM_IS_UNALIGNED_ACCESS_FAST 1
+#else
+# define LLVM_IS_UNALIGNED_ACCESS_FAST 0
+#endif
+
 #endif
diff --git a/lib/Object/ELFObjectFile.cpp b/lib/Object/ELFObjectFile.cpp
index 160053dabd8..cfe0eb467e5 100644
--- a/lib/Object/ELFObjectFile.cpp
+++ b/lib/Object/ELFObjectFile.cpp
@@ -27,30 +27,42 @@ ObjectFile *ObjectFile::createELFObjectFile(MemoryBuffer *Object) {
     1ULL << CountTrailingZeros_64(uintptr_t(Object->getBufferStart()));
 
   if (Ident.first == ELF::ELFCLASS32 && Ident.second == ELF::ELFDATA2LSB)
+#if !LLVM_IS_UNALIGNED_ACCESS_FAST
     if (MaxAlignment >= 4)
       return new ELFObjectFile<ELFType<support::little, 4, false> >(Object, ec);
-    else if (MaxAlignment >= 2)
+    else
+#endif
+    if (MaxAlignment >= 2)
       return new ELFObjectFile<ELFType<support::little, 2, false> >(Object, ec);
     else
       llvm_unreachable("Invalid alignment for ELF file!");
   else if (Ident.first == ELF::ELFCLASS32 && Ident.second == ELF::ELFDATA2MSB)
+#if !LLVM_IS_UNALIGNED_ACCESS_FAST
     if (MaxAlignment >= 4)
       return new ELFObjectFile<ELFType<support::big, 4, false> >(Object, ec);
-    else if (MaxAlignment >= 2)
+    else
+#endif
+    if (MaxAlignment >= 2)
       return new ELFObjectFile<ELFType<support::big, 2, false> >(Object, ec);
     else
       llvm_unreachable("Invalid alignment for ELF file!");
   else if (Ident.first == ELF::ELFCLASS64 && Ident.second == ELF::ELFDATA2MSB)
+#if !LLVM_IS_UNALIGNED_ACCESS_FAST
     if (MaxAlignment >= 8)
       return new ELFObjectFile<ELFType<support::big, 8, true> >(Object, ec);
-    else if (MaxAlignment >= 2)
+    else
+#endif
+    if (MaxAlignment >= 2)
       return new ELFObjectFile<ELFType<support::big, 2, true> >(Object, ec);
     else
       llvm_unreachable("Invalid alignment for ELF file!");
   else if (Ident.first == ELF::ELFCLASS64 && Ident.second == ELF::ELFDATA2LSB) {
+#if !LLVM_IS_UNALIGNED_ACCESS_FAST
     if (MaxAlignment >= 8)
       return new ELFObjectFile<ELFType<support::little, 8, true> >(Object, ec);
-    else if (MaxAlignment >= 2)
+    else
+#endif
+    if (MaxAlignment >= 2)
       return new ELFObjectFile<ELFType<support::little, 2, true> >(Object, ec);
     else
       llvm_unreachable("Invalid alignment for ELF file!");