[turbofan] Add the RoundInt32ToFloat32 operator to turbofan.

src/compiler/wasm-compiler.cc

 // Copyright 2015 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/wasm-compiler.h"
 
 #include "src/isolate-inl.h"
 
 #include "src/base/platform/platform.h"
 
@@ skipping 678 matching lines @@
     case wasm::kExprF32ConvertF64:
       op = m->TruncateFloat64ToFloat32();
       break;
     case wasm::kExprF64SConvertI32:
       op = m->ChangeInt32ToFloat64();
       break;
     case wasm::kExprF64UConvertI32:
       op = m->ChangeUint32ToFloat64();
       break;
     case wasm::kExprF32SConvertI32:
-      op = m->ChangeInt32ToFloat64();  // TODO(titzer): two conversions
-      input = graph()->NewNode(op, input);
-      op = m->TruncateFloat64ToFloat32();
+      op = m->RoundInt32ToFloat32();
       break;
     case wasm::kExprF32UConvertI32:
       op = m->ChangeUint32ToFloat64();
       input = graph()->NewNode(op, input);
       op = m->TruncateFloat64ToFloat32();
       break;
     case wasm::kExprI32SConvertF32:
       return BuildI32SConvertF32(input);
     case wasm::kExprI32UConvertF32:
       return BuildI32UConvertF32(input);
@@ skipping 1310 matching lines @@
     code->Disassemble(buffer.start(), os);
   }
 #endif
   return code;
 }
 
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8