[turbofan] ARM64: Use zr for zeroing stack slots

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/compilation-info.h"
 #include "src/compiler/code-generator-impl.h"
@@ skipping 1938 matching lines @@
       }
       if (destination->IsStackSlot()) {
         __ Str(dst, g.ToMemOperand(destination, masm()));
       }
     } else if (src.type() == Constant::kFloat32) {
       if (destination->IsFPRegister()) {
         FPRegister dst = g.ToDoubleRegister(destination).S();
         __ Fmov(dst, src.ToFloat32());
       } else {
         DCHECK(destination->IsFPStackSlot());
-        UseScratchRegisterScope scope(masm());
-        FPRegister temp = scope.AcquireS();
-        __ Fmov(temp, src.ToFloat32());
-        __ Str(temp, g.ToMemOperand(destination, masm()));
+        if (bit_cast<int32_t>(src.ToFloat32()) == 0) {
+          __ Str(wzr, g.ToMemOperand(destination, masm()));
+        } else {
+          UseScratchRegisterScope scope(masm());
+          FPRegister temp = scope.AcquireS();
+          __ Fmov(temp, src.ToFloat32());
+          __ Str(temp, g.ToMemOperand(destination, masm()));
+        }
       }
     } else {
       DCHECK_EQ(Constant::kFloat64, src.type());
       if (destination->IsFPRegister()) {
         FPRegister dst = g.ToDoubleRegister(destination);
         __ Fmov(dst, src.ToFloat64());
       } else {
         DCHECK(destination->IsFPStackSlot());
-        UseScratchRegisterScope scope(masm());
-        FPRegister temp = scope.AcquireD();
-        __ Fmov(temp, src.ToFloat64());
-        __ Str(temp, g.ToMemOperand(destination, masm()));
+        if (bit_cast<int64_t>(src.ToFloat64()) == 0) {
+          __ Str(xzr, g.ToMemOperand(destination, masm()));
+        } else {
+          UseScratchRegisterScope scope(masm());
+          FPRegister temp = scope.AcquireD();
+          __ Fmov(temp, src.ToFloat64());
+          __ Str(temp, g.ToMemOperand(destination, masm()));
+        }
       }
     }
   } else if (source->IsFPRegister()) {
     FPRegister src = g.ToDoubleRegister(source);
     if (destination->IsFPRegister()) {
       FPRegister dst = g.ToDoubleRegister(destination);
       __ Fmov(dst, src);
     } else {
       DCHECK(destination->IsFPStackSlot());
       __ Str(src, g.ToMemOperand(destination, masm()));
@@ skipping 97 matching lines @@
       padding_size -= kInstructionSize;
     }
   }
 }
 
 #undef __
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8