Add static analysis to AST expressions that records whether a negative zero w...

src/ia32/codegen-ia32.cc

 // Copyright 2010 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 1084 matching lines @@
     default:
       UNREACHABLE();
   }
   UNREACHABLE();
   return NumberInfo::Unknown();
 }
 
 
 void CodeGenerator::GenericBinaryOperation(Token::Value op,
                                            StaticType* type,
-                                           OverwriteMode overwrite_mode) {
+                                           OverwriteMode overwrite_mode,
+                                           bool no_negative_zero) {
   Comment cmnt(masm_, "[ BinaryOperation");
   Comment cmnt_token(masm_, Token::String(op));
 
   if (op == Token::COMMA) {
     // Simply discard left value.
     frame_->Nip(1);
     return;
   }
 
   Result right = frame_->Pop();
@@ skipping 47 matching lines @@
   Result answer;
   if (left_is_non_smi_constant || right_is_non_smi_constant) {
     // Go straight to the slow case, with no smi code.
     GenericBinaryOpStub stub(op,
                              overwrite_mode,
                              NO_SMI_CODE_IN_STUB,
                              operands_type);
     answer = stub.GenerateCall(masm_, frame_, &left, &right);
   } else if (right_is_smi_constant) {
     answer = ConstantSmiBinaryOperation(op, &left, right.handle(),
-                                        type, false, overwrite_mode);
+                                        type, false, overwrite_mode,
+                                        no_negative_zero);
   } else if (left_is_smi_constant) {
     answer = ConstantSmiBinaryOperation(op, &right, left.handle(),
-                                        type, true, overwrite_mode);
+                                        type, true, overwrite_mode,
+                                        no_negative_zero);
   } else {
     // Set the flags based on the operation, type and loop nesting level.
     // Bit operations always assume they likely operate on Smis. Still only
     // generate the inline Smi check code if this operation is part of a loop.
     // For all other operations only inline the Smi check code for likely smis
     // if the operation is part of a loop.
     if (loop_nesting() > 0 &&
         (Token::IsBitOp(op) ||
          operands_type.IsInteger32() ||
          type->IsLikelySmi())) {
-      answer = LikelySmiBinaryOperation(op, &left, &right, overwrite_mode);
+      answer = LikelySmiBinaryOperation(op, &left, &right,
+                                        overwrite_mode, no_negative_zero);
     } else {
       GenericBinaryOpStub stub(op,
                                overwrite_mode,
                                NO_GENERIC_BINARY_FLAGS,
                                operands_type);
       answer = stub.GenerateCall(masm_, frame_, &left, &right);
     }
   }
 
   answer.set_number_info(result_type);
@@ skipping 86 matching lines @@
                                Register left, Register right, Register scratch,
                                NumberInfo left_info, NumberInfo right_info,
                                DeferredInlineBinaryOperation* deferred);
 
 
 // Implements a binary operation using a deferred code object and some
 // inline code to operate on smis quickly.
 Result CodeGenerator::LikelySmiBinaryOperation(Token::Value op,
                                                Result* left,
                                                Result* right,
-                                               OverwriteMode overwrite_mode) {
+                                               OverwriteMode overwrite_mode,
+                                               bool no_negative_zero) {
   Result answer;
   // Special handling of div and mod because they use fixed registers.
   if (op == Token::DIV || op == Token::MOD) {
     // We need eax as the quotient register, edx as the remainder
     // register, neither left nor right in eax or edx, and left copied
     // to eax.
     Result quotient;
     Result remainder;
     bool left_is_in_eax = false;
     // Step 1: get eax for quotient.
@@ skipping 83 matching lines @@
     __ test(right->reg(), Operand(right->reg()));
     deferred->Branch(zero);
     // Divide edx:eax by the right operand.
     __ idiv(right->reg());
 
     // Complete the operation.
     if (op == Token::DIV) {
       // Check for negative zero result.  If result is zero, and divisor
       // is negative, return a floating point negative zero.  The
       // virtual frame is unchanged in this block, so local control flow
-      // can use a Label rather than a JumpTarget.
-      Label non_zero_result;
-      __ test(left->reg(), Operand(left->reg()));
-      __ j(not_zero, &non_zero_result);
-      __ test(right->reg(), Operand(right->reg()));
-      deferred->Branch(negative);
-      __ bind(&non_zero_result);
+      // can use a Label rather than a JumpTarget.  If the context of this
+      // expression will treat -0 like 0, do not do this test.
+      if (!no_negative_zero) {
+        Label non_zero_result;
+        __ test(left->reg(), Operand(left->reg()));
+        __ j(not_zero, &non_zero_result);
+        __ test(right->reg(), Operand(right->reg()));
+        deferred->Branch(negative);
+        __ bind(&non_zero_result);
+      }
       // Check for the corner case of dividing the most negative smi by
       // -1. We cannot use the overflow flag, since it is not set by
       // idiv instruction.
       ASSERT(kSmiTag == 0 && kSmiTagSize == 1);
       __ cmp(eax, 0x40000000);
       deferred->Branch(equal);
       // Check that the remainder is zero.
       __ test(edx, Operand(edx));
       deferred->Branch(not_zero);
       // Tag the result and store it in the quotient register.
       __ SmiTag(eax);
       deferred->BindExit();
       left->Unuse();
       right->Unuse();
       answer = quotient;
     } else {
       ASSERT(op == Token::MOD);
       // Check for a negative zero result.  If the result is zero, and
       // the dividend is negative, return a floating point negative
       // zero.  The frame is unchanged in this block, so local control
       // flow can use a Label rather than a JumpTarget.
-      Label non_zero_result;
-      __ test(edx, Operand(edx));
-      __ j(not_zero, &non_zero_result, taken);
-      __ test(left->reg(), Operand(left->reg()));
-      deferred->Branch(negative);
-      __ bind(&non_zero_result);
+      if (!no_negative_zero) {
+        Label non_zero_result;
+        __ test(edx, Operand(edx));
+        __ j(not_zero, &non_zero_result, taken);
+        __ test(left->reg(), Operand(left->reg()));
+        deferred->Branch(negative);
+        __ bind(&non_zero_result);
+      }
       deferred->BindExit();
       left->Unuse();
       right->Unuse();
       answer = remainder;
     }
     ASSERT(answer.is_valid());
     return answer;
   }
 
   // Special handling of shift operations because they use fixed
@@ skipping 122 matching lines @@
       // Left-hand operand has been copied into answer.
       __ SmiUntag(answer.reg());
       // Do multiplication of smis, leaving result in answer.
       __ imul(answer.reg(), Operand(right->reg()));
       // Go slow on overflows.
       deferred->Branch(overflow);
       // Check for negative zero result.  If product is zero, and one
       // argument is negative, go to slow case.  The frame is unchanged
       // in this block, so local control flow can use a Label rather
       // than a JumpTarget.
-      Label non_zero_result;
-      __ test(answer.reg(), Operand(answer.reg()));
-      __ j(not_zero, &non_zero_result, taken);
-      __ mov(answer.reg(), left->reg());
-      __ or_(answer.reg(), Operand(right->reg()));
-      deferred->Branch(negative);
-      __ xor_(answer.reg(), Operand(answer.reg()));  // Positive 0 is correct.
-      __ bind(&non_zero_result);
+      if (!no_negative_zero) {
+        Label non_zero_result;
+        __ test(answer.reg(), Operand(answer.reg()));
+        __ j(not_zero, &non_zero_result, taken);
+        __ mov(answer.reg(), left->reg());
+        __ or_(answer.reg(), Operand(right->reg()));
+        deferred->Branch(negative);
+        __ xor_(answer.reg(), Operand(answer.reg()));  // Positive 0 is correct.
+        __ bind(&non_zero_result);
+      }
       break;
     }
 
     case Token::BIT_OR:
       __ or_(answer.reg(), Operand(right->reg()));
       break;
 
     case Token::BIT_AND:
       __ and_(answer.reg(), Operand(right->reg()));
       break;
@@ skipping 218 matching lines @@
   igostub.GenerateCall(masm_, dst_, value_);
   if (!dst_.is(eax)) __ mov(dst_, eax);
 }
 
 
 Result CodeGenerator::ConstantSmiBinaryOperation(Token::Value op,
                                                  Result* operand,
                                                  Handle<Object> value,
                                                  StaticType* type,
                                                  bool reversed,
-                                                 OverwriteMode overwrite_mode) {
+                                                 OverwriteMode overwrite_mode,
+                                                 bool no_negative_zero) {
   // NOTE: This is an attempt to inline (a bit) more of the code for
   // some possible smi operations (like + and -) when (at least) one
   // of the operands is a constant smi.
   // Consumes the argument "operand".
   // TODO(199): Optimize some special cases of operations involving a
   // smi literal (multiply by 2, shift by 0, etc.).
   if (IsUnsafeSmi(value)) {
     Result unsafe_operand(value);
     if (reversed) {
       return LikelySmiBinaryOperation(op, &unsafe_operand, operand,
-                                      overwrite_mode);
+                                      overwrite_mode, no_negative_zero);
     } else {
       return LikelySmiBinaryOperation(op, operand, &unsafe_operand,
-                                      overwrite_mode);
+                                      overwrite_mode, no_negative_zero);
     }
   }
 
   // Get the literal value.
   Smi* smi_value = Smi::cast(*value);
   int int_value = smi_value->value();
 
   Result answer;
   switch (op) {
     case Token::ADD: {
@@ skipping 59 matching lines @@
       }
       deferred->BindExit();
       operand->Unuse();
       break;
     }
 
     case Token::SAR:
       if (reversed) {
         Result constant_operand(value);
         answer = LikelySmiBinaryOperation(op, &constant_operand, operand,
-                                          overwrite_mode);
+                                          overwrite_mode, no_negative_zero);
       } else {
         // Only the least significant 5 bits of the shift value are used.
         // In the slow case, this masking is done inside the runtime call.
         int shift_value = int_value & 0x1f;
         operand->ToRegister();
         frame_->Spill(operand->reg());
         if (!operand->number_info().IsSmi()) {
           DeferredInlineSmiOperation* deferred =
               new DeferredInlineSmiOperation(op,
                                              operand->reg(),
@@ skipping 15 matching lines @@
           }
         }
         answer = *operand;
       }
       break;
 
     case Token::SHR:
       if (reversed) {
         Result constant_operand(value);
         answer = LikelySmiBinaryOperation(op, &constant_operand, operand,
-                                          overwrite_mode);
+                                          overwrite_mode, no_negative_zero);
       } else {
         // Only the least significant 5 bits of the shift value are used.
         // In the slow case, this masking is done inside the runtime call.
         int shift_value = int_value & 0x1f;
         operand->ToRegister();
         answer = allocator()->Allocate();
         ASSERT(answer.is_valid());
         DeferredInlineSmiOperation* deferred =
             new DeferredInlineSmiOperation(op,
                                            answer.reg(),
@@ skipping 172 matching lines @@
         deferred->Branch(not_zero);  // Branch if non-smi or odd smi.
         __ sar(operand->reg(), 1);
         deferred->BindExit();
         answer = *operand;
       } else {
         // Cannot fall through MOD to default case, so we duplicate the
         // default case here.
         Result constant_operand(value);
         if (reversed) {
           answer = LikelySmiBinaryOperation(op, &constant_operand, operand,
-                                            overwrite_mode);
+                                            overwrite_mode, no_negative_zero);
         } else {
           answer = LikelySmiBinaryOperation(op, operand, &constant_operand,
-                                            overwrite_mode);
+                                            overwrite_mode, no_negative_zero);
         }
       }
       break;
     // Generate inline code for mod of powers of 2 and negative powers of 2.
     case Token::MOD:
       if (!reversed &&
           int_value != 0 &&
           (IsPowerOf2(int_value) || IsPowerOf2(-int_value))) {
         operand->ToRegister();
         frame_->Spill(operand->reg());
@@ skipping 16 matching lines @@
         deferred->BindExit();
         answer = *operand;
         break;
       }
       // Fall through if we did not find a power of 2 on the right hand side!
 
     default: {
       Result constant_operand(value);
       if (reversed) {
         answer = LikelySmiBinaryOperation(op, &constant_operand, operand,
-                                          overwrite_mode);
+                                          overwrite_mode, no_negative_zero);
       } else {
         answer = LikelySmiBinaryOperation(op, operand, &constant_operand,
-                                          overwrite_mode);
+                                          overwrite_mode, no_negative_zero);
       }
       break;
     }
   }
   ASSERT(answer.is_valid());
   return answer;
 }
 
 
 static bool CouldBeNaN(const Result& result) {
@@ skipping 2746 matching lines @@
   if (node->is_compound()) {
     Result result = LoadFromSlotCheckForArguments(slot, NOT_INSIDE_TYPEOF);
     frame()->Push(&result);
     Load(node->value());
 
     bool overwrite_value =
         (node->value()->AsBinaryOperation() != NULL &&
          node->value()->AsBinaryOperation()->ResultOverwriteAllowed());
     GenericBinaryOperation(node->binary_op(),
                            node->type(),
-                           overwrite_value ? OVERWRITE_RIGHT : NO_OVERWRITE);
+                           overwrite_value ? OVERWRITE_RIGHT : NO_OVERWRITE,
+                           node->no_negative_zero());
   } else {
     Load(node->value());
   }
 
   // Perform the assignment.
   if (var->mode() != Variable::CONST || node->op() == Token::INIT_CONST) {
     CodeForSourcePosition(node->position());
     StoreToSlot(slot,
                 node->op() == Token::INIT_CONST ? CONST_INIT : NOT_CONST_INIT);
   }
@@ skipping 56 matching lines @@
     }
     Result value = EmitNamedLoad(name, var != NULL);
     frame()->Push(&value);
     Load(node->value());
 
     bool overwrite_value =
         (node->value()->AsBinaryOperation() != NULL &&
          node->value()->AsBinaryOperation()->ResultOverwriteAllowed());
     GenericBinaryOperation(node->binary_op(),
                            node->type(),
-                           overwrite_value ? OVERWRITE_RIGHT : NO_OVERWRITE);
+                           overwrite_value ? OVERWRITE_RIGHT : NO_OVERWRITE,
+                           node->no_negative_zero());
   } else {
     Load(node->value());
   }
 
   // Perform the assignment.  It is safe to ignore constants here.
   ASSERT(var == NULL || var->mode() != Variable::CONST);
   ASSERT_NE(Token::INIT_CONST, node->op());
   if (is_trivial_receiver) {
     Result value = frame()->Pop();
     frame()->Push(prop->obj());
@@ skipping 58 matching lines @@
     frame()->PushElementAt(1);
     Result value = EmitKeyedLoad();
     frame()->Push(&value);
     Load(node->value());
 
     bool overwrite_value =
         (node->value()->AsBinaryOperation() != NULL &&
          node->value()->AsBinaryOperation()->ResultOverwriteAllowed());
     GenericBinaryOperation(node->binary_op(),
                            node->type(),
-                           overwrite_value ? OVERWRITE_RIGHT : NO_OVERWRITE);
+                           overwrite_value ? OVERWRITE_RIGHT : NO_OVERWRITE,
+                           node->no_negative_zero());
   } else {
     Load(node->value());
   }
 
   // Perform the assignment.  It is safe to ignore constants here.
   ASSERT(node->op() != Token::INIT_CONST);
   CodeForSourcePosition(node->position());
   Result answer = EmitKeyedStore(prop->key()->type());
   frame()->Push(&answer);
 
@@ skipping 1741 matching lines @@
 
     if (node->left()->IsTrivial()) {
       Load(node->right());
       Result right = frame_->Pop();
       frame_->Push(node->left());
       frame_->Push(&right);
     } else {
       Load(node->left());
       Load(node->right());
     }
-    GenericBinaryOperation(node->op(), node->type(), overwrite_mode);
+    GenericBinaryOperation(node->op(), node->type(),
+                           overwrite_mode, node->no_negative_zero());
   }
 }
 
 
 void CodeGenerator::VisitThisFunction(ThisFunction* node) {
   frame_->PushFunction();
 }
 
 
 void CodeGenerator::VisitCompareOperation(CompareOperation* node) {
@@ skipping 4932 matching lines @@
 
   // Call the runtime; it returns -1 (less), 0 (equal), or 1 (greater)
   // tagged as a small integer.
   __ bind(&runtime);
   __ TailCallRuntime(Runtime::kStringCompare, 2, 1);
 }
 
 #undef __
 
 } }  // namespace v8::internal