The compiler can generate smulbb perfectly well nowadays.

include/core/SkColorPriv.h

 /*
  * Copyright 2006 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.
  */
 
 #ifndef SkColorPriv_DEFINED
 #define SkColorPriv_DEFINED
 
@@ skipping 175 matching lines @@
  *  This is slightly more accurate than SkAlpha255To256.
  */
 static inline unsigned Sk255To256(U8CPU value) {
     SkASSERT(SkToU8(value) == value);
     return value + (value >> 7);
 }
 
 /** Multiplify value by 0..256, and shift the result down 8
     (i.e. return (value * alpha256) >> 8)
  */
-#define SkAlphaMul(value, alpha256)     (SkMulS16(value, alpha256) >> 8)
+#define SkAlphaMul(value, alpha256)     (((value) * (alpha256)) >> 8)
 
 //  The caller may want negative values, so keep all params signed (int)
 //  so we don't accidentally slip into unsigned math and lose the sign
 //  extension when we shift (in SkAlphaMul)
 static inline int SkAlphaBlend(int src, int dst, int scale256) {
     SkASSERT((unsigned)scale256 <= 256);
     return dst + SkAlphaMul(src - dst, scale256);
 }
 
 /**
  *  Returns (src * alpha + dst * (255 - alpha)) / 255
  *
  *  This is more accurate than SkAlphaBlend, but slightly slower
  */
 static inline int SkAlphaBlend255(S16CPU src, S16CPU dst, U8CPU alpha) {
     SkASSERT((int16_t)src == src);
     SkASSERT((int16_t)dst == dst);
     SkASSERT((uint8_t)alpha == alpha);
 
-    int prod = SkMulS16(src - dst, alpha) + 128;
+    int prod = (src - dst) * alpha + 128;
     prod = (prod + (prod >> 8)) >> 8;
     return dst + prod;
 }
 
 #define SK_R16_BITS     5
 #define SK_G16_BITS     6
 #define SK_B16_BITS     5
 
 #define SK_R16_SHIFT    (SK_B16_BITS + SK_G16_BITS)
 #define SK_G16_SHIFT    (SK_B16_BITS)
@@ skipping 816 matching lines @@
     int srcG = SkColorGetG(src);
     int srcB = SkColorGetB(src);
 
     for (int i = 0; i < width; i++) {
         dst[i] = SkBlendLCD16Opaque(srcR, srcG, srcB, dst[i], mask[i],
                                     opaqueDst);
     }
 }
 
 #endif