Polyfill BitCount for ARM/ARM64 on MSVC.

Also _WIN64 implies _WIN32.

Bug: angleproject:2858
Change-Id: I63e2ffd2e9e304171ea6adb99836733981cc1813
Reviewed-on: https://chromium-review.googlesource.com/1248441
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>

src/common/mathutil.cpp

@@ -70,4 +70,15 @@ void convert999E5toRGBFloats(unsigned int input, float *red, float *green, float
     *blue = inputData->B * pow(2.0f, (int)inputData->E - g_sharedexp_bias - g_sharedexp_mantissabits);
 }
 
+int BitCountPolyfill(uint32_t bits)
+{
+    int ones = 0;
+    while (bits)
+    {
+        ones += bool(bits & 1);
+        bits >>= 1;
+    }
+    return ones;
+}
+
 }  // namespace gl

src/common/mathutil.h

@@ -929,26 +929,30 @@ inline uint32_t BitfieldReverse(uint32_t value)
 }
 
 // Count the 1 bits.
-#if defined(ANGLE_PLATFORM_WINDOWS)
+#if defined(_M_IX86) || defined(_M_X64)
+#define ANGLE_HAS_BITCOUNT_32
 inline int BitCount(uint32_t bits)
 {
     return static_cast<int>(__popcnt(bits));
 }
-#if defined(ANGLE_IS_64_BIT_CPU)
+#if defined(_M_X64)
+#define ANGLE_HAS_BITCOUNT_64
 inline int BitCount(uint64_t bits)
 {
     return static_cast<int>(__popcnt64(bits));
 }
-#endif  // defined(ANGLE_IS_64_BIT_CPU)
-#endif  // defined(ANGLE_PLATFORM_WINDOWS)
+#endif  // defined(_M_X64)
+#endif  // defined(_M_IX86) || defined(_M_X64)
 
 #if defined(ANGLE_PLATFORM_POSIX)
+#define ANGLE_HAS_BITCOUNT_32
 inline int BitCount(uint32_t bits)
 {
     return __builtin_popcount(bits);
 }
 
 #if defined(ANGLE_IS_64_BIT_CPU)
+#define ANGLE_HAS_BITCOUNT_64
 inline int BitCount(uint64_t bits)
 {
     return __builtin_popcountll(bits);
@@ -956,6 +960,24 @@ inline int BitCount(uint64_t bits)
 #endif  // defined(ANGLE_IS_64_BIT_CPU)
 #endif  // defined(ANGLE_PLATFORM_POSIX)
 
+int BitCountPolyfill(uint32_t bits);
+
+#if !defined(ANGLE_HAS_BITCOUNT_32)
+inline int BitCount(const uint32_t bits)
+{
+    return BitCountPolyfill(bits);
+}
+#endif  // !defined(ANGLE_HAS_BITCOUNT_32)
+
+#if !defined(ANGLE_HAS_BITCOUNT_64)
+inline int BitCount(const uint64_t bits)
+{
+    return BitCount(static_cast<uint32_t>(bits >> 32)) + BitCount(static_cast<uint32_t>(bits));
+}
+#endif  // !defined(ANGLE_HAS_BITCOUNT_64)
+#undef ANGLE_HAS_BITCOUNT_32
+#undef ANGLE_HAS_BITCOUNT_64
+
 inline int BitCount(uint8_t bits)
 {
     return BitCount(static_cast<uint32_t>(bits));

src/common/platform.h

@@ -9,7 +9,7 @@
 #ifndef COMMON_PLATFORM_H_
 #define COMMON_PLATFORM_H_
 
-#if defined(_WIN32) || defined(_WIN64)
+#if defined(_WIN32)
 #   define ANGLE_PLATFORM_WINDOWS 1
 #elif defined(__APPLE__)
 #   define ANGLE_PLATFORM_APPLE 1