[turbofan] Implemented the optional Float32RoundDown operator.

src/compiler/arm64/instruction-codes-arm64.h

 // 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.
 
 #ifndef V8_COMPILER_ARM64_INSTRUCTION_CODES_ARM64_H_
 #define V8_COMPILER_ARM64_INSTRUCTION_CODES_ARM64_H_
 
 namespace v8 {
 namespace internal {
 namespace compiler {
@@ skipping 70 matching lines @@
   V(Arm64PokePair)                 \
   V(Arm64Float32Cmp)               \
   V(Arm64Float32Add)               \
   V(Arm64Float32Sub)               \
   V(Arm64Float32Mul)               \
   V(Arm64Float32Div)               \
   V(Arm64Float32Max)               \
   V(Arm64Float32Min)               \
   V(Arm64Float32Abs)               \
   V(Arm64Float32Sqrt)              \
+  V(Arm64Float32RoundDown)         \
   V(Arm64Float64Cmp)               \
   V(Arm64Float64Add)               \
   V(Arm64Float64Sub)               \
   V(Arm64Float64Mul)               \
   V(Arm64Float64Div)               \
   V(Arm64Float64Mod)               \
   V(Arm64Float64Max)               \
   V(Arm64Float64Min)               \
   V(Arm64Float64Abs)               \
   V(Arm64Float64Neg)               \
@@ skipping 60 matching lines @@
   V(Operand2_R_UXTB)  /* %r0 UXTB (unsigned extend byte) */     \
   V(Operand2_R_UXTH)  /* %r0 UXTH (unsigned extend halfword) */ \
   V(Operand2_R_SXTB)  /* %r0 SXTB (signed extend byte) */       \
   V(Operand2_R_SXTH)  /* %r0 SXTH (signed extend halfword) */
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_ARM64_INSTRUCTION_CODES_ARM64_H_