arm: First step towards dynamic NEON support.

This patch adds minimal support for dynamic ARM NEON support,
i.e. the ability to probe the CPU at runtime for NEON and
provide alternate code paths when it is available.

- Add include/core/SkUtilsArm.h, which declares a few helper
  macros (e.g. SK_NEON_ARM_IS_DYNAMIC), plus the handy
  function 'sk_cpu_arm_has_neon()' which returns true if
  the target CPU supports the ARM NEON instruction set.

  Note that the header is in include/core/ because it will
  have to be included from NEON-specific code under src/code/

  It would probably be more logical to put it under include/opts/
  instead, but this would require moving all the NEON-specific
  stuff under src/code/ into src/opts/, which is not trivial
  due to the way the code is currently architected.

- Add src/core/SkUtilsArm.cpp which implements
  'sk_cpu_arm_has_neon' for ARM-based Linux systems, only
  when SK_NEON_ARM_IS_DYNAMIC is true.

  (For other cases, 'sk_cpu_arm_has_neon' is an inline function
   that returns a constant 'true' or 'false' value).

  There is no user-level accessible CPUID instruction on ARM,
  so do all CPU feature probing by parsing /proc/cpuinfo.
  This is Linux-specific.

  For Debug build types, the CPU probing result is printed
  to the Android log (or Linux command-line) for easier
  debugging.

- Create a new 'opts_neon' target (static library) which shall
  contain all the NEON-specific code paths for the library.

  This is necessary because -mfpu=neon impacts also non-scalar
  code. Just like with -mssse3 on x86, we can't build the rest
  of the library with this flag.

  Note that for now, we only include memset16_neon and
  memset32_neon in this library.

- Modify opts_check_arm.cpp to implement SK_ARM_NEON_IS_DYNAMIC
  properly.

Compared to a 'xoom' build, the only difference is the use of
NEON-optimized memset16/32 functions. Later patches will move
more NEON-specific code paths to 'opts_neon'.
Review URL: https://codereview.appspot.com/6247058

git-svn-id: http://skia.googlecode.com/svn/trunk@4069 2bbb7eff-a529-9590-31e7-b0007b416f81

1 files changed, 178 insertions, 0 deletions

diff --git a/src/core/SkUtilsArm.cpp b/src/core/SkUtilsArm.cpp
new file mode 100644
index 0000000000..4f6ef3a76a
--- /dev/null
+++ b/src/core/SkUtilsArm.cpp
@@ -0,0 +1,178 @@
+
+/*
+ * Copyright 2012 The Android Open Source Project
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "SkUtilsArm.h"
+
+#if SK_ARM_NEON_IS_DYNAMIC
+
+#include <unistd.h>
+#include <fcntl.h>
+#include <errno.h>
+#include <string.h>
+#include <pthread.h>
+
+// Set NEON_DEBUG to 1 to allow debugging of the CPU features probing.
+// For now, we always set it for SK_DEBUG builds.
+#ifdef SK_DEBUG
+#  define NEON_DEBUG  1
+#else
+#  define NEON_DEBUG 0
+#endif
+
+#if NEON_DEBUG
+#  ifdef SK_BUILD_FOR_ANDROID
+     // used to declare PROP_VALUE_MAX and __system_property_get()
+#    include <sys/system_properties.h>
+#  endif
+#endif
+
+// A function used to determine at runtime if the target CPU supports
+// the ARM NEON instruction set. This implementation is Linux-specific.
+static bool sk_cpu_arm_check_neon(void)
+{
+    bool result = false;
+
+#if NEON_DEBUG
+    // Allow forcing the mode through the environment during debugging.
+#  ifdef SK_BUILD_FOR_ANDROID
+    // On Android, we use a system property
+#   define PROP_NAME  "debug.skia.arm_neon_mode"
+    char prop[PROP_VALUE_MAX];
+    if (__system_property_get(PROP_NAME, prop) > 0) {
+#  else
+#   define PROP_NAME   "SKIA_ARM_NEON_MODE"
+    // On ARM Linux, we use an environment variable
+    const char* prop = getenv(PROP_NAME);
+    if (prop != NULL) {
+#  endif
+        SkDebugf("%s: %s", PROP_NAME, prop);
+        if (!strcmp(prop, "1")) {
+            SkDebugf("Forcing ARM Neon mode to full!\n");
+            return true;
+        }
+        if (!strcmp(prop, "0")) {
+            SkDebugf("Disabling ARM NEON mode\n");
+            return false;
+        }
+    }
+    SkDebugf("Running dynamic CPU feature detection\n");
+#endif
+
+    // There is no user-accessible CPUID instruction on ARM that we can use.
+    // Instead, we must parse /proc/cpuinfo and look for the 'neon' feature.
+    // For example, here's a typical output (Nexus S running ICS 4.0.3):
+    /*
+    Processor       : ARMv7 Processor rev 2 (v7l)
+    BogoMIPS        : 994.65
+    Features        : swp half thumb fastmult vfp edsp thumbee neon vfpv3 
+    CPU implementer : 0x41
+    CPU architecture: 7
+    CPU variant     : 0x2
+    CPU part        : 0xc08
+    CPU revision    : 2
+
+    Hardware        : herring
+    Revision        : 000b
+    Serial          : 3833c77d6dc000ec
+    */
+    char   buffer[4096];
+
+    // If we fail any of the following, assume we don't have NEON instructions
+    // This allows us to return immediately in case of error.
+    result = false;
+
+    do {
+        // open /proc/cpuinfo
+        int fd = TEMP_FAILURE_RETRY(open("/proc/cpuinfo", O_RDONLY));
+        if (fd < 0) {
+            SkDebugf("Could not open /proc/cpuinfo: %s\n", strerror(errno));
+            break;
+        }
+
+        // Read the file. To simplify our search, we're going to place two
+        // sentinel '\n' characters: one at the start of the buffer, and one at
+        // the end. This means we reserve the first and last buffer bytes.
+        buffer[0] = '\n';
+        int size = TEMP_FAILURE_RETRY(read(fd, buffer+1, sizeof(buffer)-2));
+        close(fd);
+
+        if (size < 0) {  // should not happen
+            SkDebugf("Could not read /proc/cpuinfo: %s\n", strerror(errno));
+            break;
+        }
+
+        SkDebugf("START /proc/cpuinfo:\n%.*s\nEND /proc/cpuinfo\n",
+                 size, buffer+1);
+
+        // Compute buffer limit, and place final sentinel
+        char* buffer_end = buffer + 1 + size;
+        buffer_end[0] = '\n';
+
+        // Now, find a line that starts with "Features", i.e. look for
+        // '\nFeatures ' in our buffer.
+        const char features[] = "\nFeatures\t";
+        const size_t features_len = sizeof(features)-1;
+
+        char*  line = (char*) memmem(buffer, buffer_end - buffer,
+                                     features, features_len);
+        if (line == NULL) {  // Weird, no Features line, bad kernel?
+            SkDebugf("Could not find a line starting with 'Features'"
+              "in /proc/cpuinfo ?\n");
+            break;
+        }
+
+        line += features_len;  // Skip the "\nFeatures\t" prefix
+
+        // Find the end of the current line
+        char* line_end = (char*) memchr(line, '\n', buffer_end - line);
+        if (line_end == NULL)
+            line_end = buffer_end;
+
+        // Now find an instance of 'neon' in the flags list. We want to
+        // ensure it's only 'neon' and not something fancy like 'noneon'
+        // so check that it follows a space.
+        const char neon[] = " neon";
+        const size_t neon_len = sizeof(neon)-1;
+        const char* flag = (const char*) memmem(line, line_end - line,
+                                                neon, neon_len);
+        if (flag == NULL)
+            break;
+
+        // Ensure it is followed by a space or a newline.
+        if (flag[neon_len] != ' ' && flag[neon_len] != '\n')
+            break;
+
+        // Fine, we support Arm NEON !
+        result = true;
+
+    } while (0);
+
+    if (result) {
+        SkDebugf("Device supports ARM NEON instructions!\n");
+    } else {
+        SkDebugf("Device does NOT support ARM NEON instructions!\n");
+    }
+    return result;
+}
+
+static pthread_once_t  sOnce;
+static bool            sHasArmNeon;
+
+// called through pthread_once()
+void sk_cpu_arm_probe_features(void)
+{
+    sHasArmNeon = sk_cpu_arm_check_neon();
+}
+
+bool sk_cpu_arm_has_neon(void)
+{
+    pthread_once(&sOnce, sk_cpu_arm_probe_features);
+    return sHasArmNeon;
+}
+
+#endif // SK_ARM_NEON_IS_DYNAMIC