Use the optimization level of O2 for the decompression functions on p…

…pc64le with gcc, to avoid harmful unrolling and SIMDization with O3

lib/lz4.c

@@ -117,6 +117,28 @@
 #  endif  /* _MSC_VER */
 #endif /* LZ4_FORCE_INLINE */
 
+/* LZ4_FORCE_O2_GCC_PPC64LE and LZ4_FORCE_O2_INLINE_GCC_PPC64LE
+ * Gcc on ppc64le generates an unrolled SIMDized loop for LZ4_wildCopy,
+ * together with a simple 8-byte copy loop as a fall-back path.
+ * However, this optimization hurts the decompression speed by >30%,
+ * because the execution does not go to the optimized loop
+ * for typical compressible data, and all of the preamble checks
+ * before going to the fall-back path become useless overhead.
+ * This optimization happens only with the -O3 flag, and -O2 generates
+ * a simple 8-byte copy loop.
+ * With gcc on ppc64le, all of the LZ4_decompress_* and LZ4_wildCopy
+ * functions are annotated with __attribute__((optimize("O2"))),
+ * and also LZ4_wildCopy is forcibly inlined, so that the O2 attribute
+ * of LZ4_wildCopy does not affect the compression speed.
+ */
+#if defined(__PPC64__) && defined(__LITTLE_ENDIAN__) && defined(__GNUC__)
+#  define LZ4_FORCE_O2_GCC_PPC64LE __attribute__((optimize("O2")))
+#  define LZ4_FORCE_O2_INLINE_GCC_PPC64LE __attribute__((optimize("O2"))) LZ4_FORCE_INLINE
+#else
+#  define LZ4_FORCE_O2_GCC_PPC64LE
+#  define LZ4_FORCE_O2_INLINE_GCC_PPC64LE static
+#endif
+
 #if (defined(__GNUC__) && (__GNUC__ >= 3)) || (defined(__INTEL_COMPILER) && (__INTEL_COMPILER >= 800)) || defined(__clang__)
 #  define expect(expr,value)    (__builtin_expect ((expr),(value)) )
 #else
@@ -253,7 +275,8 @@ static void LZ4_copy8(void* dst, const void* src)
 }
 
 /* customized variant of memcpy, which can overwrite up to 8 bytes beyond dstEnd */
-static void LZ4_wildCopy(void* dstPtr, const void* srcPtr, void* dstEnd)
+LZ4_FORCE_O2_INLINE_GCC_PPC64LE
+void LZ4_wildCopy(void* dstPtr, const void* srcPtr, void* dstEnd)
 {
     BYTE* d = (BYTE*)dstPtr;
     const BYTE* s = (const BYTE*)srcPtr;
@@ -1112,6 +1135,7 @@ int LZ4_saveDict (LZ4_stream_t* LZ4_dict, char* safeBuffer, int dictSize)
  *  Note that it is important for performance that this function really get inlined,
  *  in order to remove useless branches during compilation optimization.
  */
+LZ4_FORCE_O2_GCC_PPC64LE
 LZ4_FORCE_INLINE int LZ4_decompress_generic(
                  const char* const src,
                  char* const dst,
@@ -1272,16 +1296,19 @@ LZ4_FORCE_INLINE int LZ4_decompress_generic(
 }
 
 
+LZ4_FORCE_O2_GCC_PPC64LE
 int LZ4_decompress_safe(const char* source, char* dest, int compressedSize, int maxDecompressedSize)
 {
     return LZ4_decompress_generic(source, dest, compressedSize, maxDecompressedSize, endOnInputSize, full, 0, noDict, (BYTE*)dest, NULL, 0);
 }
 
+LZ4_FORCE_O2_GCC_PPC64LE
 int LZ4_decompress_safe_partial(const char* source, char* dest, int compressedSize, int targetOutputSize, int maxDecompressedSize)
 {
     return LZ4_decompress_generic(source, dest, compressedSize, maxDecompressedSize, endOnInputSize, partial, targetOutputSize, noDict, (BYTE*)dest, NULL, 0);
 }
 
+LZ4_FORCE_O2_GCC_PPC64LE
 int LZ4_decompress_fast(const char* source, char* dest, int originalSize)
 {
     return LZ4_decompress_generic(source, dest, 0, originalSize, endOnOutputSize, full, 0, withPrefix64k, (BYTE*)(dest - 64 KB), NULL, 64 KB);
@@ -1327,6 +1354,7 @@ int LZ4_setStreamDecode (LZ4_streamDecode_t* LZ4_streamDecode, const char* dicti
     If it's not possible, save the relevant part of decoded data into a safe buffer,
     and indicate where it stands using LZ4_setStreamDecode()
 */
+LZ4_FORCE_O2_GCC_PPC64LE
 int LZ4_decompress_safe_continue (LZ4_streamDecode_t* LZ4_streamDecode, const char* source, char* dest, int compressedSize, int maxOutputSize)
 {
     LZ4_streamDecode_t_internal* lz4sd = &LZ4_streamDecode->internal_donotuse;
@@ -1353,6 +1381,7 @@ int LZ4_decompress_safe_continue (LZ4_streamDecode_t* LZ4_streamDecode, const ch
     return result;
 }
 
+LZ4_FORCE_O2_GCC_PPC64LE
 int LZ4_decompress_fast_continue (LZ4_streamDecode_t* LZ4_streamDecode, const char* source, char* dest, int originalSize)
 {
     LZ4_streamDecode_t_internal* lz4sd = &LZ4_streamDecode->internal_donotuse;
@@ -1387,6 +1416,7 @@ Advanced decoding functions :
     the dictionary must be explicitly provided within parameters
 */
 
+LZ4_FORCE_O2_GCC_PPC64LE
 LZ4_FORCE_INLINE int LZ4_decompress_usingDict_generic(const char* source, char* dest, int compressedSize, int maxOutputSize, int safe, const char* dictStart, int dictSize)
 {
     if (dictSize==0)
@@ -1399,17 +1429,20 @@ LZ4_FORCE_INLINE int LZ4_decompress_usingDict_generic(const char* source, char*
     return LZ4_decompress_generic(source, dest, compressedSize, maxOutputSize, safe, full, 0, usingExtDict, (BYTE*)dest, (const BYTE*)dictStart, dictSize);
 }
 
+LZ4_FORCE_O2_GCC_PPC64LE
 int LZ4_decompress_safe_usingDict(const char* source, char* dest, int compressedSize, int maxOutputSize, const char* dictStart, int dictSize)
 {
     return LZ4_decompress_usingDict_generic(source, dest, compressedSize, maxOutputSize, 1, dictStart, dictSize);
 }
 
+LZ4_FORCE_O2_GCC_PPC64LE
 int LZ4_decompress_fast_usingDict(const char* source, char* dest, int originalSize, const char* dictStart, int dictSize)
 {
     return LZ4_decompress_usingDict_generic(source, dest, 0, originalSize, 0, dictStart, dictSize);
 }
 
 /* debug function */
+LZ4_FORCE_O2_GCC_PPC64LE
 int LZ4_decompress_safe_forceExtDict(const char* source, char* dest, int compressedSize, int maxOutputSize, const char* dictStart, int dictSize)
 {
     return LZ4_decompress_generic(source, dest, compressedSize, maxOutputSize, endOnInputSize, full, 0, usingExtDict, (BYTE*)dest, (const BYTE*)dictStart, dictSize);