V8: remove V8_HOST_CAN_READ_UNALIGNED and its uses

Fixes segfault in 32bit SmartOS when built with GCC 4.9.

This is the second of two backports from upstream v8:
1. v8/v8@90dc5c9
2. v8/v8@7cb82a7

Original commit message:

  Reland "Remove V8_HOST_CAN_READ_UNALIGNED and its uses."

  BUG=chromium:412967
  LOG=N
  R=jkummerow@chromium.org

  Review URL: https://codereview.chromium.org/571903002

  git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23938 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

V8 issue: https://code.google.com/p/chromium/issues/detail?id=412967

Fixes #25281

Reviewed-By: Julien Gilli <julien.gilli@joyent.com>
PR-URL: #25556

Author: hashseed

deps/v8/src/base/build_config.h

@@ -21,24 +21,20 @@
 // V8_HOST_ARCH_IA32 on both 32- and 64-bit x86.
 #define V8_HOST_ARCH_IA32 1
 #define V8_HOST_ARCH_32_BIT 1
-#define V8_HOST_CAN_READ_UNALIGNED 1
 #else
 #define V8_HOST_ARCH_X64 1
 #if defined(__x86_64__) && !defined(__LP64__)
 #define V8_HOST_ARCH_32_BIT 1
 #else
 #define V8_HOST_ARCH_64_BIT 1
 #endif
-#define V8_HOST_CAN_READ_UNALIGNED 1
 #endif  // __native_client__
 #elif defined(_M_IX86) || defined(__i386__)
 #define V8_HOST_ARCH_IA32 1
 #define V8_HOST_ARCH_32_BIT 1
-#define V8_HOST_CAN_READ_UNALIGNED 1
 #elif defined(__AARCH64EL__)
 #define V8_HOST_ARCH_ARM64 1
 #define V8_HOST_ARCH_64_BIT 1
-#define V8_HOST_CAN_READ_UNALIGNED 1
 #elif defined(__ARMEL__)
 #define V8_HOST_ARCH_ARM 1
 #define V8_HOST_ARCH_32_BIT 1

deps/v8/src/deoptimizer.h

@@ -17,19 +17,17 @@ namespace internal {
 
 
 static inline double read_double_value(Address p) {
-#ifdef V8_HOST_CAN_READ_UNALIGNED
-  return Memory::double_at(p);
-#else  // V8_HOST_CAN_READ_UNALIGNED
   // Prevent gcc from using load-double (mips ldc1) on (possibly)
   // non-64-bit aligned address.
+  // We assume that the address is 32-bit aligned.
+  DCHECK(IsAligned(reinterpret_cast<intptr_t>(p), kInt32Size));
   union conversion {
     double d;
     uint32_t u[2];
   } c;
-  c.u[0] = *reinterpret_cast<uint32_t*>(p);
-  c.u[1] = *reinterpret_cast<uint32_t*>(p + 4);
+  c.u[0] = Memory::uint32_at(p);
+  c.u[1] = Memory::uint32_at(p + 4);
   return c.d;
-#endif  // V8_HOST_CAN_READ_UNALIGNED
 }
 
 

deps/v8/src/objects.cc

@@ -9026,36 +9026,7 @@ template <typename Char>
 static inline bool CompareRawStringContents(const Char* const a,
                                             const Char* const b,
                                             int length) {
-  int i = 0;
-#ifndef V8_HOST_CAN_READ_UNALIGNED
-  // If this architecture isn't comfortable reading unaligned ints
-  // then we have to check that the strings are aligned before
-  // comparing them blockwise.
-  const int kAlignmentMask = sizeof(uint32_t) - 1;  // NOLINT
-  uintptr_t pa_addr = reinterpret_cast<uintptr_t>(a);
-  uintptr_t pb_addr = reinterpret_cast<uintptr_t>(b);
-  if (((pa_addr & kAlignmentMask) | (pb_addr & kAlignmentMask)) == 0) {
-#endif
-    const int kStepSize = sizeof(int) / sizeof(Char);  // NOLINT
-    int endpoint = length - kStepSize;
-    // Compare blocks until we reach near the end of the string.
-    for (; i <= endpoint; i += kStepSize) {
-      uint32_t wa = *reinterpret_cast<const uint32_t*>(a + i);
-      uint32_t wb = *reinterpret_cast<const uint32_t*>(b + i);
-      if (wa != wb) {
-        return false;
-      }
-    }
-#ifndef V8_HOST_CAN_READ_UNALIGNED
-  }
-#endif
-  // Compare the remaining characters that didn't fit into a block.
-  for (; i < length; i++) {
-    if (a[i] != b[i]) {
-      return false;
-    }
-  }
-  return true;
+  return CompareChars(a, b, length) == 0;
 }
 
 

deps/v8/src/objects.h

@@ -9313,22 +9313,33 @@ class String: public Name {
   static inline int NonAsciiStart(const char* chars, int length) {
     const char* start = chars;
     const char* limit = chars + length;
-#ifdef V8_HOST_CAN_READ_UNALIGNED
-    DCHECK(unibrow::Utf8::kMaxOneByteChar == 0x7F);
-    const uintptr_t non_ascii_mask = kUintptrAllBitsSet / 0xFF * 0x80;
-    while (chars + sizeof(uintptr_t) <= limit) {
-      if (*reinterpret_cast<const uintptr_t*>(chars) & non_ascii_mask) {
-        return static_cast<int>(chars - start);
+
+    if (length >= kIntptrSize) {
+      // Check unaligned bytes.
+      while (!IsAligned(reinterpret_cast<intptr_t>(chars), sizeof(uintptr_t))) {
+        if (static_cast<uint8_t>(*chars) > unibrow::Utf8::kMaxOneByteChar) {
+          return static_cast<int>(chars - start);
+        }
+        ++chars;
+      }
+      // Check aligned words.
+      DCHECK(unibrow::Utf8::kMaxOneByteChar == 0x7F);
+      const uintptr_t non_ascii_mask = kUintptrAllBitsSet / 0xFF * 0x80;
+      while (chars + sizeof(uintptr_t) <= limit) {
+        if (*reinterpret_cast<const uintptr_t*>(chars) & non_ascii_mask) {
+          return static_cast<int>(chars - start);
+        }
+        chars += sizeof(uintptr_t);
       }
-      chars += sizeof(uintptr_t);
     }
-#endif
+    // Check remaining unaligned bytes.
     while (chars < limit) {
       if (static_cast<uint8_t>(*chars) > unibrow::Utf8::kMaxOneByteChar) {
         return static_cast<int>(chars - start);
       }
       ++chars;
     }
+
     return static_cast<int>(chars - start);
   }
 

deps/v8/src/regexp-macro-assembler-irregexp.h

@@ -31,6 +31,7 @@ class RegExpMacroAssemblerIrregexp: public RegExpMacroAssembler {
   virtual ~RegExpMacroAssemblerIrregexp();
   // The byte-code interpreter checks on each push anyway.
   virtual int stack_limit_slack() { return 1; }
+  virtual bool CanReadUnaligned() { return false; }
   virtual void Bind(Label* label);
   virtual void AdvanceCurrentPosition(int by);  // Signed cp change.
   virtual void PopCurrentPosition();

deps/v8/src/regexp-macro-assembler.cc

@@ -24,15 +24,6 @@ RegExpMacroAssembler::~RegExpMacroAssembler() {
 }
 
 
-bool RegExpMacroAssembler::CanReadUnaligned() {
-#ifdef V8_HOST_CAN_READ_UNALIGNED
-  return true;
-#else
-  return false;
-#endif
-}
-
-
 #ifndef V8_INTERPRETED_REGEXP  // Avoid unused code, e.g., on ARM.
 
 NativeRegExpMacroAssembler::NativeRegExpMacroAssembler(Zone* zone)

deps/v8/src/regexp-macro-assembler.h

@@ -48,7 +48,7 @@ class RegExpMacroAssembler {
   // kCheckStackLimit flag to push operations (instead of kNoStackLimitCheck)
   // at least once for every stack_limit() pushes that are executed.
   virtual int stack_limit_slack() = 0;
-  virtual bool CanReadUnaligned();
+  virtual bool CanReadUnaligned() = 0;
   virtual void AdvanceCurrentPosition(int by) = 0;  // Signed cp change.
   virtual void AdvanceRegister(int reg, int by) = 0;  // r[reg] += by.
   // Continues execution from the position pushed on the top of the backtrack

deps/v8/src/runtime.cc

@@ -6491,34 +6491,38 @@ static bool FastAsciiConvert(char* dst,
   bool changed = false;
   uintptr_t or_acc = 0;
   const char* const limit = src + length;
-#ifdef V8_HOST_CAN_READ_UNALIGNED
-  // Process the prefix of the input that requires no conversion one
-  // (machine) word at a time.
-  while (src <= limit - sizeof(uintptr_t)) {
-    const uintptr_t w = *reinterpret_cast<const uintptr_t*>(src);
-    or_acc |= w;
-    if (AsciiRangeMask(w, lo, hi) != 0) {
-      changed = true;
-      break;
+
+  // dst is newly allocated and always aligned.
+  DCHECK(IsAligned(reinterpret_cast<intptr_t>(dst), sizeof(uintptr_t)));
+  // Only attempt processing one word at a time if src is also aligned.
+  if (IsAligned(reinterpret_cast<intptr_t>(src), sizeof(uintptr_t))) {
+    // Process the prefix of the input that requires no conversion one aligned
+    // (machine) word at a time.
+    while (src <= limit - sizeof(uintptr_t)) {
+      const uintptr_t w = *reinterpret_cast<const uintptr_t*>(src);
+      or_acc |= w;
+      if (AsciiRangeMask(w, lo, hi) != 0) {
+        changed = true;
+        break;
+      }
+      *reinterpret_cast<uintptr_t*>(dst) = w;
+      src += sizeof(uintptr_t);
+      dst += sizeof(uintptr_t);
+    }
+    // Process the remainder of the input performing conversion when
+    // required one word at a time.
+    while (src <= limit - sizeof(uintptr_t)) {
+      const uintptr_t w = *reinterpret_cast<const uintptr_t*>(src);
+      or_acc |= w;
+      uintptr_t m = AsciiRangeMask(w, lo, hi);
+      // The mask has high (7th) bit set in every byte that needs
+      // conversion and we know that the distance between cases is
+      // 1 << 5.
+      *reinterpret_cast<uintptr_t*>(dst) = w ^ (m >> 2);
+      src += sizeof(uintptr_t);
+      dst += sizeof(uintptr_t);
     }
-    *reinterpret_cast<uintptr_t*>(dst) = w;
-    src += sizeof(uintptr_t);
-    dst += sizeof(uintptr_t);
-  }
-  // Process the remainder of the input performing conversion when
-  // required one word at a time.
-  while (src <= limit - sizeof(uintptr_t)) {
-    const uintptr_t w = *reinterpret_cast<const uintptr_t*>(src);
-    or_acc |= w;
-    uintptr_t m = AsciiRangeMask(w, lo, hi);
-    // The mask has high (7th) bit set in every byte that needs
-    // conversion and we know that the distance between cases is
-    // 1 << 5.
-    *reinterpret_cast<uintptr_t*>(dst) = w ^ (m >> 2);
-    src += sizeof(uintptr_t);
-    dst += sizeof(uintptr_t);
   }
-#endif
   // Process the last few bytes of the input (or the whole input if
   // unaligned access is not supported).
   while (src < limit) {
@@ -6532,9 +6536,8 @@ static bool FastAsciiConvert(char* dst,
     ++src;
     ++dst;
   }
-  if ((or_acc & kAsciiMask) != 0) {
-    return false;
-  }
+
+  if ((or_acc & kAsciiMask) != 0) return false;
 
   DCHECK(CheckFastAsciiConvert(
              saved_dst, saved_src, length, changed, Converter::kIsToLower));

deps/v8/src/snapshot-source-sink.cc

@@ -24,14 +24,10 @@ SnapshotByteSource::~SnapshotByteSource() { }
 
 int32_t SnapshotByteSource::GetUnalignedInt() {
   DCHECK(position_ < length_);  // Require at least one byte left.
-#if defined(V8_HOST_CAN_READ_UNALIGNED) &&  __BYTE_ORDER == __LITTLE_ENDIAN
-  int32_t answer = *reinterpret_cast<const int32_t*>(data_ + position_);
-#else
   int32_t answer = data_[position_];
   answer |= data_[position_ + 1] << 8;
   answer |= data_[position_ + 2] << 16;
   answer |= data_[position_ + 3] << 24;
-#endif
   return answer;
 }
 

deps/v8/src/utils.h

@@ -673,20 +673,11 @@ inline int CompareCharsUnsigned(const lchar* lhs,
                                 const rchar* rhs,
                                 int chars) {
   const lchar* limit = lhs + chars;
-#ifdef V8_HOST_CAN_READ_UNALIGNED
-  if (sizeof(*lhs) == sizeof(*rhs)) {
-    // Number of characters in a uintptr_t.
-    static const int kStepSize = sizeof(uintptr_t) / sizeof(*lhs);  // NOLINT
-    while (lhs <= limit - kStepSize) {
-      if (*reinterpret_cast<const uintptr_t*>(lhs) !=
-          *reinterpret_cast<const uintptr_t*>(rhs)) {
-        break;
-      }
-      lhs += kStepSize;
-      rhs += kStepSize;
-    }
+  if (sizeof(*lhs) == sizeof(char) && sizeof(*rhs) == sizeof(char)) {
+    // memcmp compares byte-by-byte, yielding wrong results for two-byte
+    // strings on little-endian systems.
+    return memcmp(lhs, rhs, chars);
   }
-#endif
   while (lhs < limit) {
     int r = static_cast<int>(*lhs) - static_cast<int>(*rhs);
     if (r != 0) return r;
@@ -1350,15 +1341,11 @@ void CopyChars(sinkchar* dest, const sourcechar* src, int chars) {
 template <typename sourcechar, typename sinkchar>
 void CopyCharsUnsigned(sinkchar* dest, const sourcechar* src, int chars) {
   sinkchar* limit = dest + chars;
-#ifdef V8_HOST_CAN_READ_UNALIGNED
   if ((sizeof(*dest) == sizeof(*src)) &&
       (chars >= static_cast<int>(kMinComplexMemCopy / sizeof(*dest)))) {
     MemCopy(dest, src, chars * sizeof(*dest));
-    return;
-  }
-#endif
-  while (dest < limit) {
-    *dest++ = static_cast<sinkchar>(*src++);
+  } else {
+    while (dest < limit) *dest++ = static_cast<sinkchar>(*src++);
   }
 }