The compiler can generate smulbb perfectly well nowadays.

src/core/SkScan_Antihair.cpp

 
 /*
  * Copyright 2011 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 "SkScan.h"
@@ skipping 16 matching lines @@
     to. If we can improve/fix the actual calculations, then we can remove this
     step.
  */
 #define OUTSET_BEFORE_CLIP_TEST     true
 
 #define HLINE_STACK_BUFFER      100
 
 static inline int SmallDot6Scale(int value, int dot6) {
     SkASSERT((int16_t)value == value);
     SkASSERT((unsigned)dot6 <= 64);
-    return SkMulS16(value, dot6) >> 6;
+    return (value * dot6) >> 6;
 }
 
 //#define TEST_GAMMA
 
 #ifdef TEST_GAMMA
     static uint8_t gGammaTable[256];
     #define ApplyGamma(table, alpha)    (table)[alpha]
 
     static void build_gamma_table() {
         static bool gInit = false;
@@ skipping 100 matching lines @@
         }
 
         return fy - SK_Fixed1/2;
     }
 };
 
 class Horish_SkAntiHairBlitter : public SkAntiHairBlitter {
 public:
     SkFixed drawCap(int x, SkFixed fy, SkFixed dy, int mod64) override {
         fy += SK_Fixed1/2;
-        
+
         int lower_y = fy >> 16;
         uint8_t  a = (uint8_t)(fy >> 8);
         unsigned a0 = SmallDot6Scale(255 - a, mod64);
         unsigned a1 = SmallDot6Scale(a, mod64);
         this->getBlitter()->blitAntiV2(x, lower_y - 1, a0, a1);
-        
+
         return fy + dy - SK_Fixed1/2;
     }
-    
+
     SkFixed drawLine(int x, int stopx, SkFixed fy, SkFixed dy) override {
         SkASSERT(x < stopx);
-        
+
         fy += SK_Fixed1/2;
         SkBlitter* blitter = this->getBlitter();
         do {
             int lower_y = fy >> 16;
             uint8_t  a = (uint8_t)(fy >> 8);
             blitter->blitAntiV2(x, lower_y - 1, 255 - a, a);
             fy += dy;
         } while (++x < stopx);
-        
+
         return fy - SK_Fixed1/2;
     }
 };
 
 class VLine_SkAntiHairBlitter : public SkAntiHairBlitter {
 public:
     SkFixed drawCap(int y, SkFixed fx, SkFixed dx, int mod64) override {
         SkASSERT(0 == dx);
         fx += SK_Fixed1/2;
 
@@ skipping 29 matching lines @@
         }
 
         return fx - SK_Fixed1/2;
     }
 };
 
 class Vertish_SkAntiHairBlitter : public SkAntiHairBlitter {
 public:
     SkFixed drawCap(int y, SkFixed fx, SkFixed dx, int mod64) override {
         fx += SK_Fixed1/2;
-        
+
         int x = fx >> 16;
         uint8_t a = (uint8_t)(fx >> 8);
         this->getBlitter()->blitAntiH2(x - 1, y,
                                        SmallDot6Scale(255 - a, mod64), SmallDot6Scale(a, mod64));
-        
+
         return fx + dx - SK_Fixed1/2;
     }
-    
+
     SkFixed drawLine(int y, int stopy, SkFixed fx, SkFixed dx) override {
         SkASSERT(y < stopy);
         fx += SK_Fixed1/2;
         do {
             int x = fx >> 16;
             uint8_t a = (uint8_t)(fx >> 8);
             this->getBlitter()->blitAntiH2(x - 1, y, 255 - a, a);
             fx += dx;
         } while (++y < stopy);
-        
+
         return fx - SK_Fixed1/2;
     }
 };
 
 static inline SkFixed fastfixdiv(SkFDot6 a, SkFDot6 b) {
     SkASSERT((a << 16 >> 16) == a);
     SkASSERT(b != 0);
     return (a << 16) / b;
 }
 
@@ skipping 275 matching lines @@
 #endif
 
     const SkScalar max = SkIntToScalar(32767);
     const SkRect fixedBounds = SkRect::MakeLTRB(-max, -max, max, max);
 
     SkRect clipBounds;
     if (clip) {
         clipBounds.set(clip->getBounds());
         /*  We perform integral clipping later on, but we do a scalar clip first
          to ensure that our coordinates are expressible in fixed/integers.
-         
+
          antialiased hairlines can draw up to 1/2 of a pixel outside of
          their bounds, so we need to outset the clip before calling the
          clipper. To make the numerics safer, we outset by a whole pixel,
          since the 1/2 pixel boundary is important to the antihair blitter,
          we don't want to risk numerical fate by chopping on that edge.
          */
         clipBounds.outset(SK_Scalar1, SK_Scalar1);
     }
 
     for (int i = 0; i < arrayCount - 1; ++i) {
@@ skipping 440 matching lines @@
 
 void SkScan::AntiFrameRect(const SkRect& r, const SkPoint& strokeSize,
                            const SkRasterClip& clip, SkBlitter* blitter) {
     if (clip.isBW()) {
         AntiFrameRect(r, strokeSize, &clip.bwRgn(), blitter);
     } else {
         SkAAClipBlitterWrapper wrap(clip, blitter);
         AntiFrameRect(r, strokeSize, &wrap.getRgn(), wrap.getBlitter());
     }
 }