[turbofan] Implemented the optional Float32RoundDown operator.

src/compiler/arm64/code-generator-arm64.cc

 // Copyright 2014 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/arm64/frames-arm64.h"
 #include "src/arm64/macro-assembler-arm64.h"
 #include "src/compiler/code-generator-impl.h"
 #include "src/compiler/gap-resolver.h"
@@ skipping 605 matching lines @@
       Register scratch1 = i.TempRegister(1);
       auto ool = new (zone()) OutOfLineRecordWrite(this, object, index, value,
                                                    scratch0, scratch1, mode);
       __ Str(value, MemOperand(object, index));
       __ CheckPageFlagSet(object, scratch0,
                           MemoryChunk::kPointersFromHereAreInterestingMask,
                           ool->entry());
       __ Bind(ool->exit());
       break;
     }
+    case kArm64Float32RoundDown:
+      __ Frintm(i.OutputFloat32Register(), i.InputFloat32Register(0));
+      break;
     case kArm64Float64RoundDown:
       __ Frintm(i.OutputDoubleRegister(), i.InputDoubleRegister(0));
       break;
     case kArm64Float64RoundUp:
       __ Frintp(i.OutputDoubleRegister(), i.InputDoubleRegister(0));
       break;
     case kArm64Float64RoundTiesAway:
       __ Frinta(i.OutputDoubleRegister(), i.InputDoubleRegister(0));
       break;
     case kArm64Float64RoundTruncate:
@@ skipping 910 matching lines @@
       padding_size -= kInstructionSize;
     }
   }
 }
 
 #undef __
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8