Make the host endianness check an integer constant expression.

I will remove the isBigEndianHost function once I update clang.

The ifdef logic is designed to
* not use configure/cmake to avoid breaking -arch i686 -arch ppc.
* default to little endian
* be as small as possible

It looks like sys/endian.h is the preferred header on most modern BSD systems,
but it is better to change this in a followup patch as machine/endian.h is
available on FreeBSD, OpenBSD, NetBSD and OS X.

llvm-svn: 179527

include/llvm/ADT/Hashing.h

@@ -151,7 +151,7 @@ namespace detail {
 inline uint64_t fetch64(const char *p) {
   uint64_t result;
   memcpy(&result, p, sizeof(result));
-  if (sys::isBigEndianHost())
+  if (sys::IsBigEndianHost)
     return sys::SwapByteOrder(result);
   return result;
 }
@@ -159,7 +159,7 @@ inline uint64_t fetch64(const char *p) {
 inline uint32_t fetch32(const char *p) {
   uint32_t result;
   memcpy(&result, p, sizeof(result));
-  if (sys::isBigEndianHost())
+  if (sys::IsBigEndianHost)
     return sys::SwapByteOrder(result);
   return result;
 }

include/llvm/Support/Endian.h

@@ -37,7 +37,7 @@ namespace detail {
 namespace endian {
 template<typename value_type, endianness endian>
 inline value_type byte_swap(value_type value) {
-  if (endian != native && sys::isBigEndianHost() != (endian == big))
+  if (endian != native && sys::IsBigEndianHost != (endian == big))
     return sys::SwapByteOrder(value);
   return value;
 }

include/llvm/Support/Host.h

@@ -15,22 +15,30 @@
 #define LLVM_SUPPORT_HOST_H
 
 #include "llvm/ADT/StringMap.h"
+
+#if defined(__linux__)
+#include <endian.h>
+#else
+#ifndef _MSC_VER
+#include <machine/endian.h>
+#endif
+#endif
+
 #include <string>
 
 namespace llvm {
 namespace sys {
 
-  inline bool isLittleEndianHost() {
-    union {
-      int i;
-      char c;
-    };
-    i = 1;
-    return c;
-  }
+#if BYTE_ORDER == BIG_ENDIAN
+  static const bool IsBigEndianHost = true;
+#else
+  static const bool IsBigEndianHost = false;
+#endif
+
+  static const bool IsLittleEndianHost = !IsBigEndianHost;
 
   inline bool isBigEndianHost() {
-    return !isLittleEndianHost();
+    return IsBigEndianHost;
   }
 
   /// getDefaultTargetTriple() - Return the default target triple the compiler

lib/ExecutionEngine/ExecutionEngine.cpp

@@ -948,7 +948,7 @@ static void StoreIntToMemory(const APInt &IntVal, uint8_t *Dst,
   assert((IntVal.getBitWidth()+7)/8 >= StoreBytes && "Integer too small!");
   const uint8_t *Src = (const uint8_t *)IntVal.getRawData();
 
-  if (sys::isLittleEndianHost()) {
+  if (sys::IsLittleEndianHost) {
     // Little-endian host - the source is ordered from LSB to MSB.  Order the
     // destination from LSB to MSB: Do a straight copy.
     memcpy(Dst, Src, StoreBytes);
@@ -1009,7 +1009,7 @@ void ExecutionEngine::StoreValueToMemory(const GenericValue &Val,
     break;
   }
 
-  if (sys::isLittleEndianHost() != getDataLayout()->isLittleEndian())
+  if (sys::IsLittleEndianHost != getDataLayout()->isLittleEndian())
     // Host and target are different endian - reverse the stored bytes.
     std::reverse((uint8_t*)Ptr, StoreBytes + (uint8_t*)Ptr);
 }
@@ -1021,7 +1021,7 @@ static void LoadIntFromMemory(APInt &IntVal, uint8_t *Src, unsigned LoadBytes) {
   uint8_t *Dst = reinterpret_cast<uint8_t *>(
                    const_cast<uint64_t *>(IntVal.getRawData()));
 
-  if (sys::isLittleEndianHost())
+  if (sys::IsLittleEndianHost)
     // Little-endian host - the destination must be ordered from LSB to MSB.
     // The source is ordered from LSB to MSB: Do a straight copy.
     memcpy(Dst, Src, LoadBytes);

lib/ExecutionEngine/RuntimeDyld/RuntimeDyldImpl.h

@@ -202,14 +202,14 @@ protected:
 
 
   void writeInt16BE(uint8_t *Addr, uint16_t Value) {
-    if (sys::isLittleEndianHost())
+    if (sys::IsLittleEndianHost)
       Value = sys::SwapByteOrder(Value);
     *Addr     = (Value >> 8) & 0xFF;
     *(Addr+1) = Value & 0xFF;
   }
 
   void writeInt32BE(uint8_t *Addr, uint32_t Value) {
-    if (sys::isLittleEndianHost())
+    if (sys::IsLittleEndianHost)
       Value = sys::SwapByteOrder(Value);
     *Addr     = (Value >> 24) & 0xFF;
     *(Addr+1) = (Value >> 16) & 0xFF;
@@ -218,7 +218,7 @@ protected:
   }
 
   void writeInt64BE(uint8_t *Addr, uint64_t Value) {
-    if (sys::isLittleEndianHost())
+    if (sys::IsLittleEndianHost)
       Value = sys::SwapByteOrder(Value);
     *Addr     = (Value >> 56) & 0xFF;
     *(Addr+1) = (Value >> 48) & 0xFF;

lib/Object/MachOObject.cpp

@@ -61,7 +61,7 @@ static void ReadInMemoryStruct(const MachOObject &MOO,
 MachOObject::MachOObject(MemoryBuffer *Buffer_, bool IsLittleEndian_,
                          bool Is64Bit_)
   : Buffer(Buffer_), IsLittleEndian(IsLittleEndian_), Is64Bit(Is64Bit_),
-    IsSwappedEndian(IsLittleEndian != sys::isLittleEndianHost()),
+    IsSwappedEndian(IsLittleEndian != sys::IsLittleEndianHost),
     HasStringTable(false), LoadCommands(0), NumLoadedCommands(0) {
   // Load the common header.
   memcpy(&Header, Buffer->getBuffer().data(), sizeof(Header));

lib/Support/DataExtractor.cpp

@@ -20,7 +20,7 @@ static T getU(uint32_t *offset_ptr, const DataExtractor *de,
   uint32_t offset = *offset_ptr;
   if (de->isValidOffsetForDataOfSize(offset, sizeof(val))) {
     std::memcpy(&val, &Data[offset], sizeof(val));
-    if (sys::isLittleEndianHost() != isLittleEndian)
+    if (sys::IsLittleEndianHost != isLittleEndian)
       val = sys::SwapByteOrder(val);
 
     // Advance the offset

lib/Support/FoldingSet.cpp

@@ -101,7 +101,7 @@ void FoldingSetNodeID::AddString(StringRef String) {
     // Otherwise do it the hard way.
     // To be compatible with above bulk transfer, we need to take endianness
     // into account.
-    if (sys::isBigEndianHost()) {
+    if (sys::IsBigEndianHost) {
       for (Pos += 4; Pos <= Size; Pos += 4) {
         unsigned V = ((unsigned char)String[Pos - 4] << 24) |
                      ((unsigned char)String[Pos - 3] << 16) |
@@ -110,7 +110,7 @@ void FoldingSetNodeID::AddString(StringRef String) {
         Bits.push_back(V);
       }
     } else {
-      assert(sys::isLittleEndianHost() && "Unexpected host endianness");
+      assert(sys::IsLittleEndianHost && "Unexpected host endianness");
       for (Pos += 4; Pos <= Size; Pos += 4) {
         unsigned V = ((unsigned char)String[Pos - 1] << 24) |
                      ((unsigned char)String[Pos - 2] << 16) |