I feel like my clang is especially sensitive to unused variables.

src/core/SkMatrix.cpp

 /*
  * 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.
  */
 
 #include "SkMatrix.h"
 #include "Sk64.h"
 #include "SkFloatBits.h"
@@ skipping 30 matching lines @@
 enum {
     kTranslate_Shift,
     kScale_Shift,
     kAffine_Shift,
     kPerspective_Shift,
     kRectStaysRect_Shift
 };
 
 #ifdef SK_SCALAR_IS_FLOAT
     static const int32_t kScalar1Int = 0x3f800000;
-    static const int32_t kPersp1Int  = 0x3f800000;
 #else
     #define scalarAsInt(x)  (x)
     static const int32_t kScalar1Int = (1 << 16);
     static const int32_t kPersp1Int  = (1 << 30);
 #endif
 
+#ifdef SK_SCALAR_SLOW_COMPARES
+    static const int32_t kPersp1Int  = 0x3f800000;
+#endif
+
 uint8_t SkMatrix::computePerspectiveTypeMask() const {
 #ifdef SK_SCALAR_SLOW_COMPARES
     if (SkScalarAs2sCompliment(fMat[kMPersp0]) |
             SkScalarAs2sCompliment(fMat[kMPersp1]) |
             (SkScalarAs2sCompliment(fMat[kMPersp2]) - kPersp1Int)) {
         return SkToU8(kORableMasks);
     }
 #else
     // Benchmarking suggests that replacing this set of SkScalarAs2sCompliment
     // is a win, but replacing those below is not. We don't yet understand
@@ skipping 2041 matching lines @@
         rotation1->fX = cos1;
         rotation1->fY = sin1;
     }
     if (NULL != rotation2) {
         rotation2->fX = cos2;
         rotation2->fY = sin2;
     }
 
     return true;
 }