X87: [TurboFan] enable the Float64RoundDown and Float64RoundTruncate operators in x87.

src/compiler/x87/code-generator-x87.cc

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/compiler/code-generator.h"
 
 #include "src/ast/scopes.h"
 #include "src/compiler/code-generator-impl.h"
 #include "src/compiler/gap-resolver.h"
 #include "src/compiler/node-matchers.h"
@@ skipping 1073 matching lines @@
       __ fstp(0);
       __ fld_d(MemOperand(esp, 0));
       __ fsqrt();
       __ lea(esp, Operand(esp, kDoubleSize));
       __ X87SetFPUCW(0x037F);
       break;
     }
     case kX87Float64Round: {
       RoundingMode mode =
           static_cast<RoundingMode>(MiscField::decode(instr->opcode()));
-      if (mode == MiscField::encode(kRoundDown)) {
-        __ X87SetRC(0x0400);
-      } else {
-        __ X87SetRC(0x0c00);
-      }
+      // Set the correct round mode in x87 control register
+      __ X87SetRC((mode << 10));
 
       if (!instr->InputAt(0)->IsDoubleRegister()) {
         InstructionOperand* input = instr->InputAt(0);
         USE(input);
         DCHECK(input->IsDoubleStackSlot());
         __ fstp(0);
         __ fld_d(i.InputOperand(0));
       }
       __ frndint();
       __ X87SetRC(0x0000);
@@ skipping 882 matching lines @@
     int padding_size = last_lazy_deopt_pc_ + space_needed - current_pc;
     __ Nop(padding_size);
   }
 }
 
 #undef __
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8