Improvements for x87 stack handling

BUG=

Review URL: https://codereview.chromium.org/13426006

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@14179 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/hydrogen-instructions.h

@@ -3190,13 +3190,19 @@ class HConstant: public HTemplateInstruction<0> {
 
   bool InOldSpace() const { return !HEAP->InNewSpace(*handle_); }
 
+  bool IsSpecialDouble() const {
+    return has_double_value_ &&
+        (BitCast<int64_t>(double_value_) == BitCast<int64_t>(-0.0) ||
+         FixedDoubleArray::is_the_hole_nan(double_value_) ||
+         isnan(double_value_));
+  }
+
   bool ImmortalImmovable() const {
     if (has_int32_value_) {
       return false;
     }
     if (has_double_value_) {
-      if (BitCast<int64_t>(double_value_) == BitCast<int64_t>(-0.0) ||
-          isnan(double_value_)) {
+      if (IsSpecialDouble()) {
         return true;
       }
       return false;
@@ -3227,7 +3233,9 @@ class HConstant: public HTemplateInstruction<0> {
     return has_int32_value_;
   }
 
-  virtual bool EmitAtUses() { return !representation().IsDouble(); }
+  virtual bool EmitAtUses() {
+    return !representation().IsDouble() || IsSpecialDouble();
+  }
   virtual void PrintDataTo(StringStream* stream);
   virtual HType CalculateInferredType();
   bool IsInteger() { return handle()->IsSmi(); }
@@ -3246,6 +3254,16 @@ class HConstant: public HTemplateInstruction<0> {
     ASSERT(HasDoubleValue());
     return double_value_;
   }
+  bool IsTheHole() const {
+    if (HasDoubleValue() && FixedDoubleArray::is_the_hole_nan(double_value_)) {
+      return true;
+    }
+    Heap* heap = isolate()->heap();
+    if (!handle_.is_null() && *handle_ == heap->the_hole_value()) {
+      return true;
+    }
+    return false;
+  }
   bool HasNumberValue() const { return has_double_value_; }
   int32_t NumberValueAsInteger32() const {
     ASSERT(HasNumberValue());
@@ -5677,6 +5695,10 @@ class HStoreKeyed
   bool IsDehoisted() { return is_dehoisted_; }
   void SetDehoisted(bool is_dehoisted) { is_dehoisted_ = is_dehoisted; }
 
+  bool IsConstantHoleStore() {
+    return value()->IsConstant() && HConstant::cast(value())->IsTheHole();
+  }
+
   virtual void SetSideEffectDominator(GVNFlag side_effect, HValue* dominator) {
     ASSERT(side_effect == kChangesNewSpacePromotion);
     new_space_dominator_ = dominator;

src/ia32/lithium-codegen-ia32.h

@@ -68,6 +68,7 @@ class LCodeGen BASE_EMBEDDED {
         osr_pc_offset_(-1),
         last_lazy_deopt_pc_(0),
         frame_is_built_(false),
+        x87_stack_depth_(0),
         safepoints_(info->zone()),
         resolver_(this),
         expected_safepoint_kind_(Safepoint::kSimple) {
@@ -102,10 +103,17 @@ class LCodeGen BASE_EMBEDDED {
     return Immediate(ToInteger32(LConstantOperand::cast(op)));
   }
 
-  Handle<Object> ToHandle(LConstantOperand* op) const;
+  // Support for non-sse2 (x87) floating point stack handling.
+  // These functions maintain the depth of the stack (either 0 or 1)
+  void PushX87DoubleOperand(Operand src);
+  void PushX87FloatOperand(Operand src);
+  void ReadX87Operand(Operand dst);
+  bool X87StackNonEmpty() const { return x87_stack_depth_ > 0; }
+  void PopX87();
+  void CurrentInstructionReturnsX87Result();
+  void FlushX87StackIfNecessary(LInstruction* instr);
 
-  // A utility for instructions that return floating point values on X87.
-  void HandleX87FPReturnValue(LInstruction* instr);
+  Handle<Object> ToHandle(LConstantOperand* op) const;
 
   // The operand denoting the second word (the one with a higher address) of
   // a double stack slot.
@@ -129,6 +137,7 @@ class LCodeGen BASE_EMBEDDED {
                             IntegerSignedness signedness);
 
   void DoDeferredTaggedToI(LTaggedToI* instr);
+  void DoDeferredTaggedToINoSSE2(LTaggedToINoSSE2* instr);
   void DoDeferredMathAbsTaggedHeapNumber(LUnaryMathOperation* instr);
   void DoDeferredStackCheck(LStackCheck* instr);
   void DoDeferredRandom(LRandom* instr);
@@ -315,6 +324,14 @@ class LCodeGen BASE_EMBEDDED {
       LEnvironment* env,
       NumberUntagDMode mode = NUMBER_CANDIDATE_IS_ANY_TAGGED);
 
+  void EmitNumberUntagDNoSSE2(
+      Register input,
+      Register temp,
+      bool deoptimize_on_undefined,
+      bool deoptimize_on_minus_zero,
+      LEnvironment* env,
+      NumberUntagDMode mode = NUMBER_CANDIDATE_IS_ANY_TAGGED);
+
   // Emits optimized code for typeof x == "y".  Modifies input register.
   // Returns the condition on which a final split to
   // true and false label should be made, to optimize fallthrough.
@@ -404,6 +421,7 @@ class LCodeGen BASE_EMBEDDED {
   int osr_pc_offset_;
   int last_lazy_deopt_pc_;
   bool frame_is_built_;
+  int x87_stack_depth_;
 
   // Builder that keeps track of safepoints in the code. The table
   // itself is emitted at the end of the generated code.

src/ia32/lithium-gap-resolver-ia32.cc

@@ -324,6 +324,7 @@ void LGapResolver::EmitMove(int index) {
     }
 
   } else if (source->IsDoubleRegister()) {
+    if (CpuFeatures::IsSupported(SSE2)) {
       CpuFeatureScope scope(cgen_->masm(), SSE2);
       XMMRegister src = cgen_->ToDoubleRegister(source);
       if (destination->IsDoubleRegister()) {
@@ -334,7 +335,16 @@ void LGapResolver::EmitMove(int index) {
         Operand dst = cgen_->ToOperand(destination);
         __ movdbl(dst, src);
       }
+    } else {
+      // load from the register onto the stack, store in destination, which must
+      // be a double stack slot in the non-SSE2 case.
+      ASSERT(source->index() == 0);  // source is on top of the stack
+      ASSERT(destination->IsDoubleStackSlot());
+      Operand dst = cgen_->ToOperand(destination);
+      cgen_->ReadX87Operand(dst);
+    }
   } else if (source->IsDoubleStackSlot()) {
+    if (CpuFeatures::IsSupported(SSE2)) {
       CpuFeatureScope scope(cgen_->masm(), SSE2);
       ASSERT(destination->IsDoubleRegister() ||
              destination->IsDoubleStackSlot());
@@ -348,6 +358,28 @@ void LGapResolver::EmitMove(int index) {
         __ movdbl(xmm0, src);
         __ movdbl(dst, xmm0);
       }
+    } else {
+      // load from the stack slot on top of the floating point stack, and then
+      // store in destination. If destination is a double register, then it
+      // represents the top of the stack and nothing needs to be done.
+      if (destination->IsDoubleStackSlot()) {
+        Register tmp = EnsureTempRegister();
+        Operand src0 = cgen_->ToOperand(source);
+        Operand src1 = cgen_->HighOperand(source);
+        Operand dst0 = cgen_->ToOperand(destination);
+        Operand dst1 = cgen_->HighOperand(destination);
+        __ mov(tmp, src0);  // Then use tmp to copy source to destination.
+        __ mov(dst0, tmp);
+        __ mov(tmp, src1);
+        __ mov(dst1, tmp);
+      } else {
+        Operand src = cgen_->ToOperand(source);
+        if (cgen_->X87StackNonEmpty()) {
+          cgen_->PopX87();
+        }
+        cgen_->PushX87DoubleOperand(src);
+      }
+    }
   } else {
     UNREACHABLE();
   }
@@ -419,7 +451,6 @@ void LGapResolver::EmitSwap(int index) {
     __ movaps(xmm0, src);
     __ movaps(src, dst);
     __ movaps(dst, xmm0);
-
   } else if (source->IsDoubleRegister() || destination->IsDoubleRegister()) {
     CpuFeatureScope scope(cgen_->masm(), SSE2);
     // XMM register-memory swap.  We rely on having xmm0
@@ -433,7 +464,6 @@ void LGapResolver::EmitSwap(int index) {
     __ movdbl(xmm0, other);
     __ movdbl(other, reg);
     __ movdbl(reg, Operand(xmm0));
-
   } else if (source->IsDoubleStackSlot() && destination->IsDoubleStackSlot()) {
     CpuFeatureScope scope(cgen_->masm(), SSE2);
     // Double-width memory-to-memory.  Spill on demand to use a general

src/ia32/lithium-ia32.cc

@@ -91,6 +91,22 @@ void LInstruction::VerifyCall() {
 #endif
 
 
+bool LInstruction::HasDoubleRegisterResult() {
+  return HasResult() && result()->IsDoubleRegister();
+}
+
+
+bool LInstruction::HasDoubleRegisterInput() {
+  for (int i = 0; i < InputCount(); i++) {
+    LOperand* op = InputAt(i);
+    if (op->IsDoubleRegister()) {
+      return true;
+    }
+  }
+  return false;
+}
+
+
 void LInstruction::PrintTo(StringStream* stream) {
   stream->Add("%s ", this->Mnemonic());
 
@@ -542,6 +558,11 @@ LOperand* LChunkBuilder::UseFixedDouble(HValue* value, XMMRegister reg) {
 }
 
 
+LOperand* LChunkBuilder::UseX87TopOfStack(HValue* value) {
+  return Use(value, ToUnallocated(x87tos));
+}
+
+
 LOperand* LChunkBuilder::UseRegister(HValue* value) {
   return Use(value, new(zone()) LUnallocated(LUnallocated::MUST_HAVE_REGISTER));
 }
@@ -1861,20 +1882,33 @@ LInstruction* LChunkBuilder::DoChange(HChange* instr) {
                        ? TempRegister()
                        : NULL;
       LNumberUntagD* res = new(zone()) LNumberUntagD(value, temp);
+      if (CpuFeatures::IsSafeForSnapshot(SSE2)) {
         return AssignEnvironment(DefineAsRegister(res));
+      } else {
+        return AssignEnvironment(DefineX87TOS(res));
+      }
     } else {
       ASSERT(to.IsInteger32());
-      LOperand* value = UseRegister(instr->value());
       if (instr->value()->type().IsSmi()) {
+        LOperand* value = UseRegister(instr->value());
         return DefineSameAsFirst(new(zone()) LSmiUntag(value, false));
       } else {
         bool truncating = instr->CanTruncateToInt32();
+        if (CpuFeatures::IsSafeForSnapshot(SSE2)) {
+          LOperand* value = UseRegister(instr->value());
           LOperand* xmm_temp =
               (truncating && CpuFeatures::IsSupported(SSE3))
               ? NULL
               : FixedTemp(xmm1);
           LTaggedToI* res = new(zone()) LTaggedToI(value, xmm_temp);
           return AssignEnvironment(DefineSameAsFirst(res));
+        } else {
+          LOperand* value = UseFixed(instr->value(), ecx);
+          LTaggedToINoSSE2* res =
+              new(zone()) LTaggedToINoSSE2(value, TempRegister(),
+                                           TempRegister(), TempRegister());
+          return AssignEnvironment(DefineFixed(res, ecx));
+        }
       }
     }
   } else if (from.IsDouble()) {
@@ -1992,12 +2026,20 @@ LInstruction* LChunkBuilder::DoClampToUint8(HClampToUint8* instr) {
     return DefineFixed(new(zone()) LClampIToUint8(reg), eax);
   } else {
     ASSERT(input_rep.IsTagged());
+    if (CpuFeatures::IsSupported(SSE2)) {
       LOperand* reg = UseFixed(value, eax);
       // Register allocator doesn't (yet) support allocation of double
       // temps. Reserve xmm1 explicitly.
       LOperand* temp = FixedTemp(xmm1);
       LClampTToUint8* result = new(zone()) LClampTToUint8(reg, temp);
       return AssignEnvironment(DefineFixed(result, eax));
+    } else {
+      LOperand* value = UseRegister(instr->value());
+      LClampTToUint8NoSSE2* res =
+          new(zone()) LClampTToUint8NoSSE2(value, TempRegister(),
+                                           TempRegister(), TempRegister());
+      return AssignEnvironment(DefineFixed(res, ecx));
+    }
   }
 }
 
@@ -2018,10 +2060,13 @@ LInstruction* LChunkBuilder::DoConstant(HConstant* instr) {
     return DefineAsRegister(new(zone()) LConstantI);
   } else if (r.IsDouble()) {
     double value = instr->DoubleValue();
-    LOperand* temp = (BitCast<uint64_t, double>(value) != 0)
-        ? TempRegister()
-        : NULL;
+    bool value_is_zero = BitCast<uint64_t, double>(value) == 0;
+    if (CpuFeatures::IsSafeForSnapshot(SSE2)) {
+      LOperand* temp = value_is_zero ? NULL : TempRegister();
       return DefineAsRegister(new(zone()) LConstantD(temp));
+    } else {
+      return DefineX87TOS(new(zone()) LConstantD(NULL));
+    }
   } else if (r.IsTagged()) {
     return DefineAsRegister(new(zone()) LConstantT);
   } else {
@@ -2190,6 +2235,27 @@ LInstruction* LChunkBuilder::DoLoadKeyedGeneric(HLoadKeyedGeneric* instr) {
 }
 
 
+LOperand* LChunkBuilder::GetStoreKeyedValueOperand(HStoreKeyed* instr) {
+  ElementsKind elements_kind = instr->elements_kind();
+
+  // Determine if we need a byte register in this case for the value.
+  bool val_is_fixed_register =
+      elements_kind == EXTERNAL_BYTE_ELEMENTS ||
+      elements_kind == EXTERNAL_UNSIGNED_BYTE_ELEMENTS ||
+      elements_kind == EXTERNAL_PIXEL_ELEMENTS;
+  if (val_is_fixed_register) {
+    return UseFixed(instr->value(), eax);
+  }
+
+  if (!CpuFeatures::IsSafeForSnapshot(SSE2) &&
+      IsDoubleOrFloatElementsKind(elements_kind)) {
+    return UseRegisterAtStart(instr->value());
+  }
+
+  return UseRegister(instr->value());
+}
+
+
 LInstruction* LChunkBuilder::DoStoreKeyed(HStoreKeyed* instr) {
   if (!instr->is_external()) {
     ASSERT(instr->elements()->representation().IsTagged());
@@ -2198,7 +2264,12 @@ LInstruction* LChunkBuilder::DoStoreKeyed(HStoreKeyed* instr) {
 
     if (instr->value()->representation().IsDouble()) {
       LOperand* object = UseRegisterAtStart(instr->elements());
-      LOperand* val = UseTempRegister(instr->value());
+      LOperand* val = NULL;
+      if (CpuFeatures::IsSafeForSnapshot(SSE2)) {
+        val = UseRegisterAtStart(instr->value());
+      } else if (!instr->IsConstantHoleStore()) {
+        val = UseX87TopOfStack(instr->value());
+      }
       LOperand* key = UseRegisterOrConstantAtStart(instr->key());
 
       return new(zone()) LStoreKeyed(object, key, val);
@@ -2228,15 +2299,7 @@ LInstruction* LChunkBuilder::DoStoreKeyed(HStoreKeyed* instr) {
   ASSERT(instr->elements()->representation().IsExternal());
 
   LOperand* external_pointer = UseRegister(instr->elements());
-  // Determine if we need a byte register in this case for the value.
-  bool val_is_fixed_register =
-      elements_kind == EXTERNAL_BYTE_ELEMENTS ||
-      elements_kind == EXTERNAL_UNSIGNED_BYTE_ELEMENTS ||
-      elements_kind == EXTERNAL_PIXEL_ELEMENTS;
-
-  LOperand* val = val_is_fixed_register
-      ? UseFixed(instr->value(), eax)
-      : UseRegister(instr->value());
+  LOperand* val = GetStoreKeyedValueOperand(instr);
   bool clobbers_key = ExternalArrayOpRequiresTemp(
       instr->key()->representation(), elements_kind);
   LOperand* key = clobbers_key

src/ia32/lithium-ia32.h

@@ -74,6 +74,7 @@ class LCodeGen;
   V(ClampDToUint8)                              \
   V(ClampIToUint8)                              \
   V(ClampTToUint8)                              \
+  V(ClampTToUint8NoSSE2)                        \
   V(ClassOfTestAndBranch)                       \
   V(CmpIDAndBranch)                             \
   V(CmpObjectEqAndBranch)                       \
@@ -167,6 +168,7 @@ class LCodeGen;
   V(StringLength)                               \
   V(SubI)                                       \
   V(TaggedToI)                                  \
+  V(TaggedToINoSSE2)                            \
   V(ThisFunction)                               \
   V(Throw)                                      \
   V(ToFastProperties)                           \
@@ -265,6 +267,9 @@ class LInstruction: public ZoneObject {
   virtual bool HasResult() const = 0;
   virtual LOperand* result() = 0;
 
+  bool HasDoubleRegisterResult();
+  bool HasDoubleRegisterInput();
+
   LOperand* FirstInput() { return InputAt(0); }
   LOperand* Output() { return HasResult() ? result() : NULL; }
 
@@ -1088,6 +1093,10 @@ class LConstantD: public LTemplateInstruction<1, 0, 1> {
     temps_[0] = temp;
   }
 
+  virtual bool ClobbersDoubleRegisters() const {
+    return false;
+  }
+
   LOperand* temp() { return temps_[0]; }
 
   DECLARE_CONCRETE_INSTRUCTION(ConstantD, "constant-d")
@@ -2018,6 +2027,31 @@ class LTaggedToI: public LTemplateInstruction<1, 1, 1> {
 };
 
 
+// Truncating conversion from a tagged value to an int32.
+class LTaggedToINoSSE2: public LTemplateInstruction<1, 1, 3> {
+ public:
+  LTaggedToINoSSE2(LOperand* value,
+                   LOperand* temp1,
+                   LOperand* temp2,
+                   LOperand* temp3) {
+    inputs_[0] = value;
+    temps_[0] = temp1;
+    temps_[1] = temp2;
+    temps_[2] = temp3;
+  }
+
+  LOperand* value() { return inputs_[0]; }
+  LOperand* scratch() { return temps_[0]; }
+  LOperand* scratch2() { return temps_[1]; }
+  LOperand* scratch3() { return temps_[2]; }
+
+  DECLARE_CONCRETE_INSTRUCTION(TaggedToINoSSE2, "tagged-to-i-nosse2")
+  DECLARE_HYDROGEN_ACCESSOR(UnaryOperation)
+
+  bool truncating() { return hydrogen()->CanTruncateToInt32(); }
+};
+
+
 class LSmiTag: public LTemplateInstruction<1, 1, 0> {
  public:
   explicit LSmiTag(LOperand* value) {
@@ -2040,6 +2074,10 @@ class LNumberUntagD: public LTemplateInstruction<1, 1, 1> {
   LOperand* value() { return inputs_[0]; }
   LOperand* temp() { return temps_[0]; }
 
+  virtual bool ClobbersDoubleRegisters() const {
+    return false;
+  }
+
   DECLARE_CONCRETE_INSTRUCTION(NumberUntagD, "double-untag")
   DECLARE_HYDROGEN_ACCESSOR(Change);
 };
@@ -2380,6 +2418,30 @@ class LClampTToUint8: public LTemplateInstruction<1, 1, 1> {
 };
 
 
+// Truncating conversion from a tagged value to an int32.
+class LClampTToUint8NoSSE2: public LTemplateInstruction<1, 1, 3> {
+ public:
+  LClampTToUint8NoSSE2(LOperand* unclamped,
+                       LOperand* temp1,
+                       LOperand* temp2,
+                       LOperand* temp3) {
+    inputs_[0] = unclamped;
+    temps_[0] = temp1;
+    temps_[1] = temp2;
+    temps_[2] = temp3;
+  }
+
+  LOperand* unclamped() { return inputs_[0]; }
+  LOperand* scratch() { return temps_[0]; }
+  LOperand* scratch2() { return temps_[1]; }
+  LOperand* scratch3() { return temps_[2]; }
+
+  DECLARE_CONCRETE_INSTRUCTION(ClampTToUint8NoSSE2,
+                               "clamp-t-to-uint8-nosse2")
+  DECLARE_HYDROGEN_ACCESSOR(UnaryOperation)
+};
+
+
 class LCheckNonSmi: public LTemplateInstruction<0, 1, 0> {
  public:
   explicit LCheckNonSmi(LOperand* value) {
@@ -2742,6 +2804,7 @@ class LChunkBuilder BASE_EMBEDDED {
   MUST_USE_RESULT LOperand* UseFixed(HValue* value, Register fixed_register);
   MUST_USE_RESULT LOperand* UseFixedDouble(HValue* value,
                                            XMMRegister fixed_register);
+  MUST_USE_RESULT LOperand* UseX87TopOfStack(HValue* value);
 
   // A value that is guaranteed to be allocated to a register.
   // Operand created by UseRegister is guaranteed to be live until the end of
@@ -2827,6 +2890,8 @@ class LChunkBuilder BASE_EMBEDDED {
   LInstruction* DoArithmeticT(Token::Value op,
                               HArithmeticBinaryOperation* instr);
 
+  LOperand* GetStoreKeyedValueOperand(HStoreKeyed* instr);
+
   LPlatformChunk* chunk_;
   CompilationInfo* info_;
   HGraph* const graph_;

src/ia32/macro-assembler-ia32.cc

@@ -2518,6 +2518,28 @@ void MacroAssembler::Ret(int bytes_dropped, Register scratch) {
 }
 
 
+void MacroAssembler::VerifyX87StackDepth(uint depth) {
+  // Make sure the floating point stack is either empty or has depth items.
+  ASSERT(depth <= 7);
+
+  // The top-of-stack (tos) is 7 if there is one item pushed.
+  int tos = (8 - depth) % 8;
+  const int kTopMask = 0x3800;
+  push(eax);
+  fwait();
+  fnstsw_ax();
+  and_(eax, kTopMask);
+  shr(eax, 11);
+  cmp(eax, Immediate(tos));
+  Label all_ok;
+  j(equal, &all_ok);
+  Check(equal, "Unexpected FPU stack depth after instruction");
+  bind(&all_ok);
+  fnclex();
+  pop(eax);
+}
+
+
 void MacroAssembler::Drop(int stack_elements) {
   if (stack_elements > 0) {
     add(esp, Immediate(stack_elements * kPointerSize));

src/ia32/macro-assembler-ia32.h

@@ -807,6 +807,8 @@ class MacroAssembler: public Assembler {
     return code_object_;
   }
 
+  // Insert code to verify that the x87 stack has the specified depth (0-7)
+  void VerifyX87StackDepth(uint depth);
 
   // ---------------------------------------------------------------------------
   // StatsCounter support

src/lithium-allocator.cc

@@ -1788,7 +1788,7 @@ STATIC_ASSERT(DoubleRegister::kMaxNumAllocatableRegisters >=
 bool LAllocator::TryAllocateFreeReg(LiveRange* current) {
   LifetimePosition free_until_pos[DoubleRegister::kMaxNumAllocatableRegisters];
 
-  for (int i = 0; i < DoubleRegister::kMaxNumAllocatableRegisters; i++) {
+  for (int i = 0; i < num_registers_; i++) {
     free_until_pos[i] = LifetimePosition::MaxPosition();
   }
 
@@ -1880,7 +1880,7 @@ void LAllocator::AllocateBlockedReg(LiveRange* current) {
   LifetimePosition use_pos[DoubleRegister::kMaxNumAllocatableRegisters];
   LifetimePosition block_pos[DoubleRegister::kMaxNumAllocatableRegisters];
 
-  for (int i = 0; i < DoubleRegister::NumAllocatableRegisters(); i++) {
+  for (int i = 0; i < num_registers_; i++) {
     use_pos[i] = block_pos[i] = LifetimePosition::MaxPosition();
   }
 

src/objects.h

@@ -1495,6 +1495,8 @@ class HeapNumber: public HeapObject {
   static const int kExponentBits = 11;
   static const int kExponentBias = 1023;
   static const int kExponentShift = 20;
+  static const int kInfinityOrNanExponent =
+      (kExponentMask >> kExponentShift) - kExponentBias;
   static const int kMantissaBitsInTopWord = 20;
   static const int kNonMantissaBitsInTopWord = 12;
 

test/mjsunit/pixel-array-rounding.js

@@ -27,12 +27,15 @@
 
 // Flags: --allow-natives-syntax
 
-var pixels = new Uint8ClampedArray(8);
+var pixels = new Uint8ClampedArray(11);
 
 function f() {
   for (var i = 0; i < 8; i++) {
     pixels[i] = (i * 1.1);
   }
+  pixels[8] = 255.5;
+  pixels[9] = NaN;
+  pixels[10] = -0.5;
   return pixels[1] + pixels[6];
 }
 
@@ -42,3 +45,6 @@ assertEquals(6, pixels[5]);
 %OptimizeFunctionOnNextCall(f);
 f();
 assertEquals(6, pixels[5]);
+assertEquals(255, pixels[8]);
+assertEquals(0, pixels[9]);
+assertEquals(0, pixels[10]);