ARM: Create configure option --enable-arm-simd to govern assembly optimizations

configure.ac

@@ -1303,6 +1303,42 @@ AS_HELP_STRING([--enable-libsamplerate-shared], [dynamically load libsamplerate
     fi
 }
 
+dnl Check for ARM instruction support using gas syntax
+CheckARM()
+{
+    AC_ARG_ENABLE(arm-simd,
+AC_HELP_STRING([--enable-arm-simd], [use SIMD assembly blitters on ARM [[default=yes]]]),
+                  enable_arm_simd=$enableval, enable_arm_simd=yes)
+    if test x$enable_video = xyes -a x$enable_assembly = xyes -a x$enable_arm_simd = xyes; then
+        save_CFLAGS="$CFLAGS"
+        have_arm_simd=no
+        CFLAGS="-x assembler-with-cpp $CFLAGS"
+        
+        AC_MSG_CHECKING(for ARM SIMD)
+        AC_COMPILE_IFELSE([AC_LANG_SOURCE([[
+        .text
+        .arch armv6
+        .object_arch armv4
+        .arm
+        .altmacro
+        #ifndef __ARM_EABI__
+        #error EABI is required (to be sure that calling conventions are compatible)
+        #endif
+        pld [r0]
+        uqadd8 r0, r0, r0
+        ]])], have_arm_simd=yes)
+        AC_MSG_RESULT($have_arm_simd)
+        
+        CFLAGS="$save_CFLAGS"
+        
+        if test x$have_arm_simd = xyes; then
+            AC_DEFINE(SDL_ARM_SIMD_BLITTERS)
+dnl            SOURCES="$SOURCES $srcdir/src/video/arm/pixman-arm-simd*.c"
+            SOURCES="$SOURCES $srcdir/src/video/arm/pixman-arm-simd*.S"
+        fi
+    fi
+}
+
 dnl See if GCC's -fvisibility=hidden is supported (gcc4 and later, usually).
 dnl  Details of this flag are here: http://gcc.gnu.org/wiki/Visibility
 CheckVisibilityHidden()
@@ -3396,6 +3432,7 @@ case "$host" in
         CheckDiskAudio
         CheckDummyAudio
         CheckDLOPEN
+        CheckARM
         CheckOSS
         CheckALSA
         CheckPulseAudio

include/SDL_config.h.in

@@ -407,6 +407,7 @@
 /* Enable assembly routines */
 #undef SDL_ASSEMBLY_ROUTINES
 #undef SDL_ALTIVEC_BLITTERS
+#undef SDL_ARM_SIMD_BLITTERS
 
 /* Enable ime support */
 #undef SDL_USE_IME

include/SDL_cpuinfo.h

@@ -186,6 +186,11 @@ extern DECLSPEC SDL_bool SDLCALL SDL_HasAVX2(void);
  */
 extern DECLSPEC SDL_bool SDLCALL SDL_HasAVX512F(void);
 
+/**
+ *  This function returns true if the CPU has ARM SIMD (ARMv6) features.
+ */
+extern DECLSPEC SDL_bool SDLCALL SDL_HasARMSIMD(void);
+
 /**
  *  This function returns true if the CPU has NEON (ARM SIMD) features.
  */

src/cpuinfo/SDL_cpuinfo.c

@@ -96,6 +96,7 @@
 #define CPU_HAS_AVX2    (1 << 10)
 #define CPU_HAS_NEON    (1 << 11)
 #define CPU_HAS_AVX512F (1 << 12)
+#define CPU_HAS_ARM_SIMD (1 << 13)
 
 #if SDL_ALTIVEC_BLITTERS && HAVE_SETJMP && !__MACOSX__ && !__OpenBSD__
 /* This is the brute force way of detecting instruction sets...
@@ -325,7 +326,50 @@ CPU_haveAltiVec(void)
     return altivec;
 }
 
-#if defined(__LINUX__) && defined(__ARM_ARCH) && !defined(HAVE_GETAUXVAL)
+#ifdef __linux__
+
+#include <unistd.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <elf.h>
+
+static SDL_bool
+CPU_haveARMSIMD(void)
+{
+    int arm_simd = 0;
+    int fd;
+
+    fd = open("/proc/self/auxv", O_RDONLY);
+    if (fd >= 0)
+    {
+        Elf32_auxv_t aux;
+        while (read(fd, &aux, sizeof aux) == sizeof aux)
+        {
+            if (aux.a_type == AT_PLATFORM)
+            {
+                const char *plat = (const char *) aux.a_un.a_val;
+                arm_simd = strncmp(plat, "v6l", 3) == 0 ||
+                           strncmp(plat, "v7l", 3) == 0;
+            }
+        }
+        close(fd);
+    }
+    return arm_simd;
+}
+
+#else
+
+static SDL_bool
+CPU_haveARMSIMD(void)
+{
+#warning SDL_HasARMSIMD is not implemented for this ARM platform. Write me.
+    return 0;
+}
+
+#endif
+
+#if (defined(__LINUX__) || defined(__ANDROID__)) && defined(__ARM_ARCH) && !defined(HAVE_GETAUXVAL)
 static int
 readProcAuxvForNeon(void)
 {
@@ -668,6 +712,10 @@ SDL_GetCPUFeatures(void)
             SDL_CPUFeatures |= CPU_HAS_AVX512F;
             SDL_SIMDAlignment = SDL_max(SDL_SIMDAlignment, 64);
         }
+        if (CPU_haveARMSIMD()) {
+            SDL_CPUFeatures |= CPU_HAS_ARM_SIMD;
+            SDL_SIMDAlignment = SDL_max(SDL_SIMDAlignment, 16);
+        }
         if (CPU_haveNEON()) {
             SDL_CPUFeatures |= CPU_HAS_NEON;
             SDL_SIMDAlignment = SDL_max(SDL_SIMDAlignment, 16);
@@ -749,6 +797,12 @@ SDL_HasAVX512F(void)
     return CPU_FEATURE_AVAILABLE(CPU_HAS_AVX512F);
 }
 
+SDL_bool
+SDL_HasARMSIMD(void)
+{
+    return CPU_FEATURE_AVAILABLE(CPU_HAS_ARM_SIMD);
+}
+
 SDL_bool
 SDL_HasNEON(void)
 {
@@ -870,6 +924,7 @@ main()
     printf("AVX: %d\n", SDL_HasAVX());
     printf("AVX2: %d\n", SDL_HasAVX2());
     printf("AVX-512F: %d\n", SDL_HasAVX512F());
+    printf("ARM SIMD: %d\n", SDL_HasARMSIMD());
     printf("NEON: %d\n", SDL_HasNEON());
     printf("RAM: %d MB\n", SDL_GetSystemRAM());
     return 0;