Convert String array index/length hash to BitField

R=verwaest@chromium.org

Review URL: https://codereview.chromium.org/300023011

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21533 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

diff --git a/src/arm/macro-assembler-arm.cc b/src/arm/macro-assembler-arm.cc
index d1bbe7e..5b649e3 100644 (file)
--- a/src/arm/macro-assembler-arm.cc
+++ b/src/arm/macro-assembler-arm.cc
@@ -2439,10 +2439,7 @@ void MacroAssembler::IndexFromHash(Register hash, Register index) {
   // conflict.
   ASSERT(TenToThe(String::kMaxCachedArrayIndexLength) <
          (1 << String::kArrayIndexValueBits));
-  // We want the smi-tagged index in key.  kArrayIndexValueMask has zeros in
-  // the low kHashShift bits.
-  Ubfx(hash, hash, String::kHashShift, String::kArrayIndexValueBits);
-  SmiTag(index, hash);
+  DecodeFieldToSmi<String::ArrayIndexValueBits>(index, hash);
 }
 
 

diff --git a/src/arm/macro-assembler-arm.h b/src/arm/macro-assembler-arm.h
index 4000478..5f77be6 100644 (file)
--- a/src/arm/macro-assembler-arm.h
+++ b/src/arm/macro-assembler-arm.h
@@ -1357,17 +1357,33 @@ class MacroAssembler: public Assembler {
 
   template<typename Field>
   void DecodeField(Register dst, Register src) {
+    Ubfx(dst, src, Field::kShift, Field::kSize);
+  }
+
+  template<typename Field>
+  void DecodeField(Register reg) {
+    DecodeField<Field>(reg, reg);
+  }
+
+  template<typename Field>
+  void DecodeFieldToSmi(Register dst, Register src) {
     static const int shift = Field::kShift;
-    static const int mask = Field::kMask >> shift;
-    static const int size = Field::kSize;
-    mov(dst, Operand(src, LSR, shift));
-    if (shift + size != 32) {
+    static const int mask = Field::kMask >> shift << kSmiTagSize;
+    STATIC_ASSERT((mask & (0x80000000u >> (kSmiTagSize - 1))) == 0);
+    STATIC_ASSERT(kSmiTag == 0);
+    if (shift < kSmiTagSize) {
+      mov(dst, Operand(src, LSL, kSmiTagSize - shift));
+      and_(dst, dst, Operand(mask));
+    } else if (shift > kSmiTagSize) {
+      mov(dst, Operand(src, LSR, shift - kSmiTagSize));
       and_(dst, dst, Operand(mask));
+    } else {
+      and_(dst, src, Operand(mask));
     }
   }
 
   template<typename Field>
-  void DecodeField(Register reg) {
+  void DecodeFieldToSmi(Register reg) {
     DecodeField<Field>(reg, reg);
   }
 

diff --git a/src/arm64/macro-assembler-arm64.cc b/src/arm64/macro-assembler-arm64.cc
index cd7f0ae..ff85931 100644 (file)
--- a/src/arm64/macro-assembler-arm64.cc
+++ b/src/arm64/macro-assembler-arm64.cc
@@ -3975,11 +3975,8 @@ void MacroAssembler::IndexFromHash(Register hash, Register index) {
   // conflict.
   ASSERT(TenToThe(String::kMaxCachedArrayIndexLength) <
          (1 << String::kArrayIndexValueBits));
-  // We want the smi-tagged index in key.  kArrayIndexValueMask has zeros in
-  // the low kHashShift bits.
-  STATIC_ASSERT(kSmiTag == 0);
-  Ubfx(hash, hash, String::kHashShift, String::kArrayIndexValueBits);
-  SmiTag(index, hash);
+  DecodeField<String::ArrayIndexValueBits>(index, hash);
+  SmiTag(index, index);
 }
 
 

diff --git a/src/ia32/macro-assembler-ia32.cc b/src/ia32/macro-assembler-ia32.cc
index a405c63..9674ef1 100644 (file)
--- a/src/ia32/macro-assembler-ia32.cc
+++ b/src/ia32/macro-assembler-ia32.cc
@@ -2047,16 +2047,10 @@ void MacroAssembler::IndexFromHash(Register hash, Register index) {
   // reserved for it does not conflict.
   ASSERT(TenToThe(String::kMaxCachedArrayIndexLength) <
          (1 << String::kArrayIndexValueBits));
-  // We want the smi-tagged index in key.  kArrayIndexValueMask has zeros in
-  // the low kHashShift bits.
-  and_(hash, String::kArrayIndexValueMask);
-  STATIC_ASSERT(String::kHashShift >= kSmiTagSize && kSmiTag == 0);
-  if (String::kHashShift > kSmiTagSize) {
-    shr(hash, String::kHashShift - kSmiTagSize);
-  }
   if (!index.is(hash)) {
     mov(index, hash);
   }
+  DecodeFieldToSmi<String::ArrayIndexValueBits>(index);
 }
 
 

diff --git a/src/ia32/macro-assembler-ia32.h b/src/ia32/macro-assembler-ia32.h
index 41c0ea6..fc6a5a0 100644 (file)
--- a/src/ia32/macro-assembler-ia32.h
+++ b/src/ia32/macro-assembler-ia32.h
@@ -497,9 +497,26 @@ class MacroAssembler: public Assembler {
   void DecodeField(Register reg) {
     static const int shift = Field::kShift;
     static const int mask = Field::kMask >> Field::kShift;
-    sar(reg, shift);
+    if (shift != 0) {
+      sar(reg, shift);
+    }
     and_(reg, Immediate(mask));
   }
+
+  template<typename Field>
+  void DecodeFieldToSmi(Register reg) {
+    static const int shift = Field::kShift;
+    static const int mask = (Field::kMask >> Field::kShift) << kSmiTagSize;
+    STATIC_ASSERT((mask & (0x80000000u >> (kSmiTagSize - 1))) == 0);
+    STATIC_ASSERT(kSmiTag == 0);
+    if (shift < kSmiTagSize) {
+      shl(reg, kSmiTagSize - shift);
+    } else if (shift > kSmiTagSize) {
+      sar(reg, shift - kSmiTagSize);
+    }
+    and_(reg, Immediate(mask));
+  }
+
   void LoadPowerOf2(XMMRegister dst, Register scratch, int power);
 
   // Abort execution if argument is not a number, enabled via --debug-code.

diff --git a/src/objects.cc b/src/objects.cc
index 277d320..a7b880e 100644 (file)
--- a/src/objects.cc
+++ b/src/objects.cc
@@ -9668,7 +9668,7 @@ bool String::SlowAsArrayIndex(uint32_t* index) {
     uint32_t field = hash_field();
     if ((field & kIsNotArrayIndexMask) != 0) return false;
     // Isolate the array index form the full hash field.
-    *index = (kArrayIndexHashMask & field) >> kHashShift;
+    *index = ArrayIndexValueBits::decode(field);
     return true;
   } else {
     return ComputeArrayIndex(index);
@@ -9726,8 +9726,8 @@ uint32_t StringHasher::MakeArrayIndexHash(uint32_t value, int length) {
   ASSERT(TenToThe(String::kMaxCachedArrayIndexLength) <
          (1 << String::kArrayIndexValueBits));
 
-  value <<= String::kHashShift;
-  value |= length << String::kArrayIndexHashLengthShift;
+  value <<= String::ArrayIndexValueBits::kShift;
+  value |= length << String::ArrayIndexLengthBits::kShift;
 
   ASSERT((value & String::kIsNotArrayIndexMask) == 0);
   ASSERT((length > String::kMaxCachedArrayIndexLength) ||

diff --git a/src/objects.h b/src/objects.h
index d42ebca..9059eda 100644 (file)
--- a/src/objects.h
+++ b/src/objects.h
@@ -8793,13 +8793,11 @@ class Name: public HeapObject {
 
   STATIC_ASSERT((kArrayIndexLengthBits > 0));
 
-  static const int kArrayIndexHashLengthShift =
-      kArrayIndexValueBits + kNofHashBitFields;
-
-  static const int kArrayIndexHashMask = (1 << kArrayIndexHashLengthShift) - 1;
-
-  static const int kArrayIndexValueMask =
-      ((1 << kArrayIndexValueBits) - 1) << kHashShift;
+  class ArrayIndexValueBits : public BitField<unsigned int, kNofHashBitFields,
+      kArrayIndexValueBits> {};
+  class ArrayIndexLengthBits : public BitField<unsigned int,
+      kNofHashBitFields + kArrayIndexValueBits,
+      kArrayIndexLengthBits> {};
 
   // Check that kMaxCachedArrayIndexLength + 1 is a power of two so we
   // could use a mask to test if the length of string is less than or equal to
@@ -8807,7 +8805,7 @@ class Name: public HeapObject {
   STATIC_ASSERT(IS_POWER_OF_TWO(kMaxCachedArrayIndexLength + 1));
 
   static const unsigned int kContainsCachedArrayIndexMask =
-      (~kMaxCachedArrayIndexLength << kArrayIndexHashLengthShift) |
+      (~kMaxCachedArrayIndexLength << ArrayIndexLengthBits::kShift) |
       kIsNotArrayIndexMask;
 
   // Value of empty hash field indicating that the hash is not computed.

diff --git a/src/x64/macro-assembler-x64.cc b/src/x64/macro-assembler-x64.cc
index acff185..521b10f 100644 (file)
--- a/src/x64/macro-assembler-x64.cc
+++ b/src/x64/macro-assembler-x64.cc
@@ -548,16 +548,10 @@ void MacroAssembler::IndexFromHash(Register hash, Register index) {
   // reserved for it does not conflict.
   ASSERT(TenToThe(String::kMaxCachedArrayIndexLength) <
          (1 << String::kArrayIndexValueBits));
-  // We want the smi-tagged index in key. Even if we subsequently go to
-  // the slow case, converting the key to a smi is always valid.
-  // key: string key
-  // hash: key's hash field, including its array index value.
-  andp(hash, Immediate(String::kArrayIndexValueMask));
-  shrp(hash, Immediate(String::kHashShift));
-  // Here we actually clobber the key which will be used if calling into
-  // runtime later. However as the new key is the numeric value of a string key
-  // there is no difference in using either key.
-  Integer32ToSmi(index, hash);
+  if (!hash.is(index)) {
+    movl(index, hash);
+  }
+  DecodeFieldToSmi<String::ArrayIndexValueBits>(index);
 }
 
 

diff --git a/src/x64/macro-assembler-x64.h b/src/x64/macro-assembler-x64.h
index 34d034a..ae5a959 100644 (file)
--- a/src/x64/macro-assembler-x64.h
+++ b/src/x64/macro-assembler-x64.h
@@ -1014,10 +1014,18 @@ class MacroAssembler: public Assembler {
   void DecodeField(Register reg) {
     static const int shift = Field::kShift;
     static const int mask = Field::kMask >> Field::kShift;
-    shrp(reg, Immediate(shift));
+    if (shift != 0) {
+      shrp(reg, Immediate(shift));
+    }
     andp(reg, Immediate(mask));
   }
 
+  template<typename Field>
+  void DecodeFieldToSmi(Register reg) {
+    andp(reg, Immediate(Field::kMask));
+    shlp(reg, Immediate(kSmiShift - Field::kShift));
+  }
+
   // Abort execution if argument is not a number, enabled via --debug-code.
   void AssertNumber(Register object);