Fixed crashes exposed though fuzzing.

src/x64/full-codegen-x64.cc

Index: src/x64/full-codegen-x64.cc
diff --git a/src/x64/full-codegen-x64.cc b/src/x64/full-codegen-x64.cc
index d5fa5e5a7ca250543ce1645959151350f0b102cf..c32e8a0bbd150d4f68170d5e48fdcb47feed563f 100644
--- a/src/x64/full-codegen-x64.cc
+++ b/src/x64/full-codegen-x64.cc
@@ -3407,30 +3407,6 @@ void FullCodeGenerator::EmitDateField(CallRuntime* expr) {
 }
 
 
-void FullCodeGenerator::EmitSeqStringSetCharCheck(Register string,
-                                                  Register index,
-                                                  Register value,
-                                                  uint32_t encoding_mask) {
-  __ Check(masm()->CheckSmi(index), kNonSmiIndex);
-  __ Check(masm()->CheckSmi(value), kNonSmiValue);
-
-  __ SmiCompare(index, FieldOperand(string, String::kLengthOffset));
-  __ Check(less, kIndexIsTooLarge);
-
-  __ SmiCompare(index, Smi::FromInt(0));
-  __ Check(greater_equal, kIndexIsNegative);
-
-  __ push(value);
-  __ movq(value, FieldOperand(string, HeapObject::kMapOffset));
-  __ movzxbq(value, FieldOperand(value, Map::kInstanceTypeOffset));
-
-  __ andb(value, Immediate(kStringRepresentationMask | kStringEncodingMask));
-  __ cmpq(value, Immediate(encoding_mask));
-  __ Check(equal, kUnexpectedStringType);
-  __ pop(value);
-}
-
-
 void FullCodeGenerator::EmitOneByteSeqStringSetChar(CallRuntime* expr) {
   ZoneList<Expression*>* args = expr->arguments();
   ASSERT_EQ(3, args->length());
@@ -3446,12 +3422,18 @@ void FullCodeGenerator::EmitOneByteSeqStringSetChar(CallRuntime* expr) {
   VisitForAccumulatorValue(args->at(0));  // string
 
   if (FLAG_debug_code) {
-    static const uint32_t one_byte_seq_type = kSeqStringTag | kOneByteStringTag;
-    EmitSeqStringSetCharCheck(string, index, value, one_byte_seq_type);
+    __ ThrowIf(NegateCondition(__ CheckSmi(value)), kNonSmiValue);
+    __ ThrowIf(NegateCondition(__ CheckSmi(index)), kNonSmiValue);
   }
 
   __ SmiToInteger32(value, value);
   __ SmiToInteger32(index, index);
+
+  if (FLAG_debug_code) {
+    static const uint32_t one_byte_seq_type = kSeqStringTag | kOneByteStringTag;
+    __ EmitSeqStringSetCharCheck(string, index, value, one_byte_seq_type);
+  }
+
   __ movb(FieldOperand(string, index, times_1, SeqOneByteString::kHeaderSize),
           value);
   context()->Plug(string);
@@ -3473,12 +3455,18 @@ void FullCodeGenerator::EmitTwoByteSeqStringSetChar(CallRuntime* expr) {
   VisitForAccumulatorValue(args->at(0));  // string
 
   if (FLAG_debug_code) {
-    static const uint32_t two_byte_seq_type = kSeqStringTag | kTwoByteStringTag;
-    EmitSeqStringSetCharCheck(string, index, value, two_byte_seq_type);
+    __ ThrowIf(NegateCondition(__ CheckSmi(value)), kNonSmiValue);
+    __ ThrowIf(NegateCondition(__ CheckSmi(index)), kNonSmiValue);
   }
 
   __ SmiToInteger32(value, value);
   __ SmiToInteger32(index, index);
+
+  if (FLAG_debug_code) {
+    static const uint32_t two_byte_seq_type = kSeqStringTag | kTwoByteStringTag;
+    __ EmitSeqStringSetCharCheck(string, index, value, two_byte_seq_type);
+  }
+
   __ movw(FieldOperand(string, index, times_2, SeqTwoByteString::kHeaderSize),
           value);
   context()->Plug(rax);