feature: dynamically enable the STRHASHCRC32 optimization.

Author: thibaultcha

.travis.yml

@@ -80,8 +80,6 @@ before_install:
   - export CXX=g++-5
 
 install:
-  - if [[ "$(uname -m)" == "x86_64" ]]; then XCFLAGS="$XCFLAGS -msse4.2"; fi
-  - if [[ "$(uname -m)" == "aarch64" ]]; then XCFLAGS="$XCFLAGS -march=armv8-a+crc"; fi
   - make -j$JOBS CCDEBUG=-g Q= PREFIX=$PREFIX XCFLAGS="$XCFLAGS" >build.log 2>&1 || (cat build.log && exit 1)
   - make install PREFIX=$PREFIX >build.log 2>&1 || (cat build.log && exit 1)
   - export PATH="$PREFIX/bin:$PATH"

README.md

@@ -163,10 +163,8 @@ local newstate = jit.prngstate(123456)
 **syntax:** *ok = jit.crc32()*
 
 Returns a boolean value indicating if the current architecture supports a CRC32
-instruction set.
-
-CRC32 support will be checked at runtime if LuaJIT was compiled with `-msse4.2`
-on x64 architectures, or `-march=armv8-a+crc` on ARM64.
+instruction set. CRC32 support will be checked at runtime on x64 and ARM64
+platforms.
 
 CRC32 support allows for this branch to use an optimized string hashing
 algorithm. See the [String hashing](#string-hashing) section for details on
@@ -285,10 +283,8 @@ but makes hash collision attacks harder for strings up to 127 bytes of size
 (see `lj_str_new()`).
 
 This optimization is only available for x64 and ARM64 architectures, and will
-be enabled if:
-
-1. LuaJIT is compiled with `-msse4.2` on x64, or `-march=armv8-a+crc` on ARM64.
-2. A CRC32 instruction set is detected at runtime (see [jit.crc32](#jitcrc32)).
+be enabled if a CRC32 instruction set is detected at runtime (see
+[jit.crc32](#jitcrc32)).
 
 **Note:** This optimization can be disabled by compiling LuaJIT with
 `-DLJ_OR_DISABLE_STRHASHCRC32`.

src/Makefile

@@ -521,6 +521,15 @@ ALL_GEN= $(LJVM_S) $(ALL_HDRGEN) $(LIB_VMDEFP)
 WIN_RM= *.obj *.lib *.exp *.dll *.exe *.manifest *.pdb *.ilk
 ALL_RM= $(ALL_T) $(ALL_GEN) *.o host/*.o $(WIN_RM)
 
+ifeq (x64,$(TARGET_LJARCH))
+  lj_str_hash-CFLAGS = -msse4.2
+endif
+ifeq (arm64,$(TARGET_LJARCH))
+  lj_str_hash-CFLAGS = -march=armv8-a+crc
+endif
+
+F_CFLAGS = $($(patsubst %.c,%-CFLAGS,$<))
+
 ##############################################################################
 # Build mode handling.
 ##############################################################################
@@ -685,8 +694,8 @@ lj_folddef.h: $(BUILDVM_T) lj_opt_fold.c
 
 %.o: %.c
 	$(E) "CC        $@"
-	$(Q)$(TARGET_DYNCC) $(TARGET_ACFLAGS) -c -o $(@:.o=_dyn.o) $<
-	$(Q)$(TARGET_CC) $(TARGET_ACFLAGS) -c -o $@ $<
+	$(Q)$(TARGET_DYNCC) $(TARGET_ACFLAGS) $(F_CFLAGS) -c -o $(@:.o=_dyn.o) $<
+	$(Q)$(TARGET_CC) $(TARGET_ACFLAGS) $(F_CFLAGS) -c -o $@ $<
 
 %.o: %.S
 	$(E) "ASM       $@"

src/lib_jit.c

@@ -159,11 +159,7 @@ LJLIB_CF(jit_prngstate)
 
 LJLIB_CF(jit_crc32)
 {
-#if LJ_OR_STRHASHCRC32
   setboolV(L->top++, lj_check_crc32_support());
-#else
-  setboolV(L->top++, 0);
-#endif
   return 1;
 }
 

src/lj_arch.h

@@ -616,7 +616,7 @@ extern void *LJ_WIN_LOADLIBA(const char *path);
 #endif
 
 /* Optimized string hashing, added by OpenResty. */
-#if (LUAJIT_TARGET == LUAJIT_ARCH_X64 && defined(__SSE4_2__) || LUAJIT_TARGET == LUAJIT_ARCH_ARM64 && __ARM_FEATURE_CRC32) && defined(__GNUC__)
+#if defined(__GNUC__) && (LUAJIT_TARGET == LUAJIT_ARCH_X64 || LUAJIT_TARGET == LUAJIT_ARCH_ARM64)
 #ifndef LJ_OR_DISABLE_STRHASHCRC32
 #define LJ_OR_STRHASHCRC32 	1
 #endif

src/lj_str_hash.c

@@ -13,35 +13,39 @@
 
 #include "lj_str_hash.h"
 
-#if LJ_OR_STRHASHCRC32
+#if LUAJIT_TARGET == LUAJIT_ARCH_X64
+#include "lj_vm.h"
+
+#ifndef F_CPU_SSE4_2
+#define F_CPU_SSE4_2 	(1 << 20)
+#endif
+
+#elif LUAJIT_TARGET == LUAJIT_ARCH_ARM64
+#include <sys/auxv.h>
+#include <errno.h>
+
+#ifndef HWCAP_CRC32
+#define HWCAP_CRC32 	(1 << 7)
+#endif
+#endif
 
+#if LJ_OR_STRHASHCRC32
 #include <sys/types.h>
 #include <unistd.h>
 #include <time.h>
-#include "lj_vm.h"
 
 #if LUAJIT_TARGET == LUAJIT_ARCH_X64
 #include <smmintrin.h>
 
 #define lj_crc32_u32 	_mm_crc32_u32
 #define lj_crc32_u64 	_mm_crc32_u64
 
-#ifndef F_CPU_SSE4_2
-#define F_CPU_SSE4_2 	(1 << 20)
-#endif
-
 #elif LUAJIT_TARGET == LUAJIT_ARCH_ARM64
-#include <sys/auxv.h>
 #include <arm_acle.h>
-#include <errno.h>
 
 #define lj_crc32_u32 	__crc32cw
 #define lj_crc32_u64 	__crc32cd
 
-#ifndef HWCAP_CRC32
-#define HWCAP_CRC32 	(1 << 7)
-#endif
-
 #else
 #error "LJ_OR_STRHASHCRC32 not supported on this architecture"
 #endif
@@ -288,20 +292,6 @@ static void lj_str_hash_init_random(void)
 
 #undef POW2_MASK
 
-LJ_FUNC unsigned char lj_check_crc32_support()
-{
-#if LUAJIT_TARGET == LUAJIT_ARCH_X64
-  uint32_t features[4];
-  if (lj_vm_cpuid(1, features))
-    return (features[2] & F_CPU_SSE4_2) != 0;
-#elif LUAJIT_TARGET == LUAJIT_ARCH_ARM64
-  uint32_t hwcap = getauxval(AT_HWCAP);
-  if (hwcap != ENOENT)
-    return (hwcap & HWCAP_CRC32) != 0;
-#endif
-  return 0;
-}
-
 LJ_FUNC void lj_init_strhashfn(global_State *g)
 {
   static StrHashFunction strhashfn;
@@ -318,6 +308,20 @@ LJ_FUNC void lj_init_strhashfn(global_State *g)
 
 #endif
 
+LJ_FUNC unsigned char lj_check_crc32_support()
+{
+#if LUAJIT_TARGET == LUAJIT_ARCH_X64
+  uint32_t features[4];
+  if (lj_vm_cpuid(1, features))
+    return (features[2] & F_CPU_SSE4_2) != 0;
+#elif LUAJIT_TARGET == LUAJIT_ARCH_ARM64
+  uint32_t hwcap = getauxval(AT_HWCAP);
+  if (hwcap != ENOENT)
+    return (hwcap & HWCAP_CRC32) != 0;
+#endif
+  return 0;
+}
+
 LJ_FUNC MSize lj_str_hash_orig(const char *str, size_t lenx)
 {
   MSize len = (MSize)lenx;

src/lj_str_hash.h

@@ -4,9 +4,9 @@
 #include "lj_obj.h"
 
 LJ_FUNC MSize lj_str_hash_orig(const char *str, size_t lenx);
+LJ_FUNC unsigned char lj_check_crc32_support();
 
 #if LJ_OR_STRHASHCRC32
-LJ_FUNC unsigned char lj_check_crc32_support();
 LJ_FUNC void lj_init_strhashfn(global_State *g);
 #endif
 

t/strhashcrc32.t

@@ -13,7 +13,9 @@ __DATA__
 --- lua
 jit.off()
 
-if jit.crc32() then
+if os.getenv("NO_STRHASHCRC32") == "1" then
+    assert(jit.strhashcrc32() == false, "strhashcrc32 should be disabled (LJ_OR_DISABLE_STRHASHCRC32)")
+elseif jit.crc32() then
     assert(jit.strhashcrc32() == true, "strhashcrc32 should be enabled")
 else
     assert(jit.strhashcrc32() == false, "strhashcrc32 should be disabled")