MathSqrt and MathPowHalf do not cause any promotion.

src/hydrogen-instructions.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 2591 matching lines @@
     SetOperandAt(1, value);
     switch (op) {
       case kMathFloor:
       case kMathRound:
       case kMathCeil:
         set_representation(Representation::Integer32());
         break;
       case kMathAbs:
         // Not setting representation here: it is None intentionally.
         SetFlag(kFlexibleRepresentation);
+        // TODO(svenpanne) This flag is actually only needed if representation()
+        // is tagged, and not when it is an unboxed double or unboxed integer.
         SetGVNFlag(kChangesNewSpacePromotion);
         break;
-      case kMathSqrt:
-      case kMathPowHalf:
       case kMathLog:
       case kMathSin:
       case kMathCos:
       case kMathTan:
         set_representation(Representation::Double());
+        // These operations use the TranscendentalCache, so they may allocate.
         SetGVNFlag(kChangesNewSpacePromotion);
         break;
       case kMathExp:
+      case kMathSqrt:
+      case kMathPowHalf:
         set_representation(Representation::Double());
         break;
       default:
         UNREACHABLE();
     }
     SetFlag(kUseGVN);
   }
 
   virtual bool IsDeletable() const { return true; }
 
@@ skipping 3910 matching lines @@
   virtual bool IsDeletable() const { return true; }
 };
 
 
 #undef DECLARE_INSTRUCTION
 #undef DECLARE_CONCRETE_INSTRUCTION
 
 } }  // namespace v8::internal
 
 #endif  // V8_HYDROGEN_INSTRUCTIONS_H_