Avoid recording unnecessary deoptimization environments in a couple of places.

src/x64/lithium-x64.cc

Index: src/x64/lithium-x64.cc
===================================================================
--- src/x64/lithium-x64.cc	(revision 10324)
+++ src/x64/lithium-x64.cc	(working copy)
@@ -1033,16 +1033,25 @@
 
 
 LInstruction* LChunkBuilder::DoBranch(HBranch* instr) {
-  HValue* v = instr->value();
-  if (v->EmitAtUses()) {
-    ASSERT(v->IsConstant());
-    ASSERT(!v->representation().IsDouble());
-    HBasicBlock* successor = HConstant::cast(v)->ToBoolean()
+  HValue* value = instr->value();
+  if (value->EmitAtUses()) {
+    ASSERT(value->IsConstant());
+    ASSERT(!value->representation().IsDouble());
+    HBasicBlock* successor = HConstant::cast(value)->ToBoolean()
         ? instr->FirstSuccessor()
         : instr->SecondSuccessor();
     return new LGoto(successor->block_id());
   }
-  return AssignEnvironment(new LBranch(UseRegister(v)));
+
+  LBranch* result = new LBranch(UseRegister(value));
+  // Tagged values that are not known smis or booleans require a
+  // deoptimization environment.
+  Representation rep = value->representation();
+  HType type = value->type();
+  if (rep.IsTagged() && !type.IsSmi() && !type.IsBoolean()) {
+    return AssignEnvironment(result);
+  }
+  return result;
 }
 
 
@@ -1329,7 +1338,11 @@
     LOperand* left = UseRegisterAtStart(instr->LeastConstantOperand());
     LOperand* right = UseOrConstant(instr->MostConstantOperand());
     LMulI* mul = new LMulI(left, right);
-    return AssignEnvironment(DefineSameAsFirst(mul));
+    if (instr->CheckFlag(HValue::kCanOverflow) ||
+        instr->CheckFlag(HValue::kBailoutOnMinusZero)) {
+      AssignEnvironment(mul);
+    }
+    return DefineSameAsFirst(mul);
   } else if (instr->representation().IsDouble()) {
     return DoArithmeticD(Token::MUL, instr);
   } else {
@@ -1553,7 +1566,7 @@
 LInstruction* LChunkBuilder::DoValueOf(HValueOf* instr) {
   LOperand* object = UseRegister(instr->value());
   LValueOf* result = new LValueOf(object);
-  return AssignEnvironment(DefineSameAsFirst(result));
+  return DefineSameAsFirst(result);
 }
 
 
@@ -1866,7 +1879,8 @@
   LOperand* obj = UseRegisterAtStart(instr->object());
   LOperand* key = UseRegisterOrConstantAtStart(instr->key());
   LLoadKeyedFastElement* result = new LLoadKeyedFastElement(obj, key);
-  return AssignEnvironment(DefineAsRegister(result));
+  if (instr->RequiresHoleCheck()) AssignEnvironment(result);
+  return DefineAsRegister(result);
 }