Remove DoubleRepresentation from globals.h

The implementation of DoubleRepresentation was based on undefined
behavior, and it can be replaced by bit_casts.

BUG=chromium:623168
R=titzer@chromium.org

Review-Url: https://codereview.chromium.org/2105683006
Cr-Commit-Position: refs/heads/master@{#37390}

src/arm/macro-assembler-arm.cc

@@ -1004,13 +1004,11 @@ void MacroAssembler::VFPCompareAndLoadFlags(const DwVfpRegister src1,
 void MacroAssembler::Vmov(const DwVfpRegister dst,
                           const double imm,
                           const Register scratch) {
-  static const DoubleRepresentation minus_zero(-0.0);
-  static const DoubleRepresentation zero(0.0);
-  DoubleRepresentation value_rep(imm);
+  int64_t imm_bits = bit_cast<int64_t>(imm);
   // Handle special values first.
-  if (value_rep == zero) {
+  if (imm_bits == bit_cast<int64_t>(0.0)) {
     vmov(dst, kDoubleRegZero);
-  } else if (value_rep == minus_zero) {
+  } else if (imm_bits == bit_cast<int64_t>(-0.0)) {
     vneg(dst, kDoubleRegZero);
   } else {
     vmov(dst, imm, scratch);

src/conversions.h

@@ -149,8 +149,7 @@ char* DoubleToRadixCString(double value, int radix);
 
 
 static inline bool IsMinusZero(double value) {
-  static const DoubleRepresentation minus_zero(-0.0);
-  return DoubleRepresentation(value) == minus_zero;
+  return bit_cast<int64_t>(value) == bit_cast<int64_t>(-0.0);
 }
 
 

src/factory.cc

@@ -2161,9 +2161,8 @@ static inline int NumberCacheHash(Handle<FixedArray> cache,
   if (number->IsSmi()) {
     return Handle<Smi>::cast(number)->value() & mask;
   } else {
-    DoubleRepresentation rep(number->Number());
-    return
-        (static_cast<int>(rep.bits) ^ static_cast<int>(rep.bits >> 32)) & mask;
+    int64_t bits = bit_cast<int64_t>(number->Number());
+    return (static_cast<int>(bits) ^ static_cast<int>(bits >> 32)) & mask;
   }
 }
 

src/globals.h

@@ -633,18 +633,6 @@ typedef void (*StoreBufferCallback)(Heap* heap,
                                     MemoryChunk* page,
                                     StoreBufferEvent event);
 
-
-// Union used for fast testing of specific double values.
-union DoubleRepresentation {
-  double  value;
-  int64_t bits;
-  DoubleRepresentation(double x) { value = x; }
-  bool operator==(const DoubleRepresentation& other) const {
-    return bits == other.bits;
-  }
-};
-
-
 // Union used for customized checking of the IEEE double types
 // inlined within v8 runtime, rather than going to the underlying
 // platform headers and libraries

src/mips/macro-assembler-mips.cc

@@ -2304,13 +2304,11 @@ void MacroAssembler::Move(FPURegister dst, float imm) {
 
 
 void MacroAssembler::Move(FPURegister dst, double imm) {
-  static const DoubleRepresentation minus_zero(-0.0);
-  static const DoubleRepresentation zero(0.0);
-  DoubleRepresentation value_rep(imm);
+  int64_t imm_bits = bit_cast<int64_t>(imm);
   // Handle special values first.
-  if (value_rep == zero && has_double_zero_reg_set_) {
+  if (imm_bits == bit_cast<int64_t>(0.0) && has_double_zero_reg_set_) {
     mov_d(dst, kDoubleRegZero);
-  } else if (value_rep == minus_zero && has_double_zero_reg_set_) {
+  } else if (imm_bits == bit_cast<int64_t>(-0.0) && has_double_zero_reg_set_) {
     neg_d(dst, kDoubleRegZero);
   } else {
     uint32_t lo, hi;

src/mips64/macro-assembler-mips64.cc

@@ -2509,13 +2509,11 @@ void MacroAssembler::Move(FPURegister dst, float imm) {
 
 
 void MacroAssembler::Move(FPURegister dst, double imm) {
-  static const DoubleRepresentation minus_zero(-0.0);
-  static const DoubleRepresentation zero(0.0);
-  DoubleRepresentation value_rep(imm);
+  int64_t imm_bits = bit_cast<int64_t>(imm);
   // Handle special values first.
-  if (value_rep == zero && has_double_zero_reg_set_) {
+  if (imm_bits == bit_cast<int64_t>(0.0) && has_double_zero_reg_set_) {
     mov_d(dst, kDoubleRegZero);
-  } else if (value_rep == minus_zero && has_double_zero_reg_set_) {
+  } else if (imm_bits == bit_cast<int64_t>(-0.0) && has_double_zero_reg_set_) {
     neg_d(dst, kDoubleRegZero);
   } else {
     uint32_t lo, hi;