Fix UB in SkDivBits

include/core/SkFixed.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 SkFixed_DEFINED
 #define SkFixed_DEFINED
 
@@ skipping 64 matching lines @@
 #define SkFixedCeilToInt(x)     (((x) + SK_Fixed1 - 1) >> 16)
 #define SkFixedFloorToInt(x)    ((x) >> 16)
 
 #define SkFixedRoundToFixed(x)  (((x) + SK_FixedHalf) & 0xFFFF0000)
 #define SkFixedCeilToFixed(x)   (((x) + SK_Fixed1 - 1) & 0xFFFF0000)
 #define SkFixedFloorToFixed(x)  ((x) & 0xFFFF0000)
 
 #define SkFixedAbs(x)       SkAbs32(x)
 #define SkFixedAve(a, b)    (((a) + (b)) >> 1)
 
-#define SkFixedDiv(numer, denom)    SkDivBits(numer, denom, 16)
+// Blink layout tests are baselined to Clang optimizing through undefined behavior in SkDivBits.
+#if defined(SK_SUPPORT_LEGACY_DIVBITS_UB)
+    #define SkFixedDiv(numer, denom) SkDivBits(numer, denom, 16)
+#else
+    // TODO(reed): this clamp shouldn't be needed.  Use SkToS32().
+    #define SkFixedDiv(numer, denom) \
+        SkTPin<int32_t>(((int64_t)numer << 16) / denom, SK_MinS32, SK_MaxS32)
+#endif
 
 //////////////////////////////////////////////////////////////////////////////////////////////////////
 // Now look for ASM overrides for our portable versions (should consider putting this in its own file)
 
 inline SkFixed SkFixedMul_longlong(SkFixed a, SkFixed b) {
     return (SkFixed)((int64_t)a * b >> 16);
 }
 #define SkFixedMul(a,b)     SkFixedMul_longlong(a,b)
 
 
@@ skipping 59 matching lines @@
 #define Sk48Dot16FloorToInt(x)    static_cast<int>((x) >> 16)
 
 static inline float Sk48Dot16ToScalar(Sk48Dot16 x) {
     return static_cast<float>(x * 1.5258789e-5);  // x * (1.0f / (1 << 16))
 }
 #define SkFloatTo48Dot16(x)       (static_cast<Sk48Dot16>((x) * (1 << 16)))
 
 #define SkScalarTo48Dot16(x)      SkFloatTo48Dot16(x)
 
 #endif