Prefer loading Smi 0 instead of null into a runtime call result slot.

runtime/vm/stub_code_arm64.cc

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/globals.h"
 #if defined(TARGET_ARCH_ARM64)
 
 #include "vm/assembler.h"
 #include "vm/code_generator.h"
 #include "vm/compiler.h"
@@ skipping 306 matching lines @@
 
 
 // Input parameters:
 //   R4: arguments descriptor array.
 void StubCode::GenerateCallStaticFunctionStub(Assembler* assembler) {
   // Create a stub frame as we are pushing some objects on the stack before
   // calling into the runtime.
   __ EnterStubFrame();
   // Setup space on stack for return value and preserve arguments descriptor.
   __ Push(R4);
-  __ PushObject(Object::null_object());
+  __ Push(ZR);
   __ CallRuntime(kPatchStaticCallRuntimeEntry, 0);
   // Get Code object result and restore arguments descriptor array.
   __ Pop(CODE_REG);
   __ Pop(R4);
   // Remove the stub frame.
   __ LeaveStubFrame();
   // Jump to the dart function.
   __ LoadFieldFromOffset(R0, CODE_REG, Code::entry_point_offset());
   __ br(R0);
 }
 
 
 // Called from a static call only when an invalid code has been entered
 // (invalid because its function was optimized or deoptimized).
 // R4: arguments descriptor array.
 void StubCode::GenerateFixCallersTargetStub(Assembler* assembler) {
   // Load code pointer to this stub from the thread:
   // The one that is passed in, is not correct - it points to the code object
   // that needs to be replaced.
   __ ldr(CODE_REG, Address(THR, Thread::fix_callers_target_code_offset()));
   // Create a stub frame as we are pushing some objects on the stack before
   // calling into the runtime.
   __ EnterStubFrame();
   // Setup space on stack for return value and preserve arguments descriptor.
   __ Push(R4);
-  __ PushObject(Object::null_object());
+  __ Push(ZR);
   __ CallRuntime(kFixCallersTargetRuntimeEntry, 0);
   // Get Code object result and restore arguments descriptor array.
   __ Pop(CODE_REG);
   __ Pop(R4);
   // Remove the stub frame.
   __ LeaveStubFrame();
   // Jump to the dart function.
   __ LoadFieldFromOffset(R0, CODE_REG, Code::entry_point_offset());
   __ br(R0);
 }
 
 
 // Called from object allocate instruction when the allocation stub has been
 // disabled.
 void StubCode::GenerateFixAllocationStubTargetStub(Assembler* assembler) {
   // Load code pointer to this stub from the thread:
   // The one that is passed in, is not correct - it points to the code object
   // that needs to be replaced.
   __ ldr(CODE_REG, Address(THR, Thread::fix_allocation_stub_code_offset()));
   __ EnterStubFrame();
   // Setup space on stack for return value.
-  __ PushObject(Object::null_object());
+  __ Push(ZR);
   __ CallRuntime(kFixAllocationStubTargetRuntimeEntry, 0);
   // Get Code object result.
   __ Pop(CODE_REG);
   // Remove the stub frame.
   __ LeaveStubFrame();
   // Jump to the dart function.
   __ LoadFieldFromOffset(R0, CODE_REG, Code::entry_point_offset());
   __ br(R0);
 }
 
@@ skipping 170 matching lines @@
   // When lazily generated invocation dispatchers are disabled, the
   // miss-handler may return null.
   __ CompareObject(R0, Object::null_object());
   __ b(call_target_function, NE);
   __ EnterStubFrame();
 
   // Load the receiver.
   __ LoadFieldFromOffset(R2, R4, ArgumentsDescriptor::count_offset());
   __ add(TMP, FP, Operand(R2, LSL, 2));  // R2 is Smi.
   __ LoadFromOffset(R6, TMP, kParamEndSlotFromFp * kWordSize);
-  __ PushObject(Object::null_object());
+  __ Push(ZR);  // Result slot.
   __ Push(R6);  // Receiver.
   __ Push(R5);  // ICData/MegamorphicCache.
   __ Push(R4);  // Arguments descriptor.
   // R2: Smi-tagged arguments array length.
   PushArgumentsArray(assembler);
   const intptr_t kNumArgs = 4;
   __ CallRuntime(kInvokeNoSuchMethodDispatcherRuntimeEntry, kNumArgs);
   __ Drop(4);
   __ Pop(R0);  // Return value.
   __ LeaveStubFrame();
@@ skipping 10 matching lines @@
   __ LoadFromOffset(R6, TMP, kParamEndSlotFromFp * kWordSize);
 
   // Preserve IC data and arguments descriptor.
   __ Push(R5);
   __ Push(R4);
 
   // Push space for the return value.
   // Push the receiver.
   // Push IC data object.
   // Push arguments descriptor array.
-  __ PushObject(Object::null_object());
+  __ Push(ZR);
   __ Push(R6);
   __ Push(R5);
   __ Push(R4);
   __ CallRuntime(kMegamorphicCacheMissHandlerRuntimeEntry, 3);
   // Remove arguments.
   __ Drop(3);
   __ Pop(R0);  // Get result into R0 (target function).
 
   // Restore IC data and arguments descriptor.
   __ Pop(R4);
@@ skipping 141 matching lines @@
   __ ret();
 
   // Unable to allocate the array using the fast inline code, just call
   // into the runtime.
   __ Bind(&slow_case);
   // Create a stub frame as we are pushing some objects on the stack before
   // calling into the runtime.
   __ EnterStubFrame();
   // Setup space on stack for return value.
   // Push array length as Smi and element type.
-  __ PushObject(Object::null_object());
+  __ Push(ZR);
   __ Push(R2);
   __ Push(R1);
   __ CallRuntime(kAllocateArrayRuntimeEntry, 2);
   // Pop arguments; result is popped in IP.
   __ Pop(R1);
   __ Pop(R2);
   __ Pop(R0);
   __ LeaveStubFrame();
   __ ret();
 }
@@ skipping 412 matching lines @@
     // R0: new object.
     __ ret();
 
     __ Bind(&slow_case);
   }
   // If is_cls_parameterized:
   // R1: new object type arguments.
   // Create a stub frame as we are pushing some objects on the stack before
   // calling into the runtime.
   __ EnterStubFrame();  // Uses pool pointer to pass cls to runtime.
-  // Setup space on stack for return value.
-  __ PushObject(Object::null_object());
+  __ Push(ZR);  // Result slot.
   __ PushObject(cls);  // Push class of object to be allocated.
   if (is_cls_parameterized) {
     // Push type arguments.
     __ Push(R1);
   } else {
     // Push null type arguments.
     __ PushObject(Object::null_object());
   }
   __ CallRuntime(kAllocateObjectRuntimeEntry, 2);  // Allocate object.
   __ Drop(2);  // Pop arguments.
@@ skipping 16 matching lines @@
   __ EnterStubFrame();
 
   // Load the receiver.
   __ LoadFieldFromOffset(R2, R4, ArgumentsDescriptor::count_offset());
   __ add(TMP, FP, Operand(R2, LSL, 2));  // R2 is Smi.
   __ LoadFromOffset(R6, TMP, kParamEndSlotFromFp * kWordSize);
 
   // Push space for the return value.
   // Push the receiver.
   // Push arguments descriptor array.
-  __ PushObject(Object::null_object());
+  __ Push(ZR);
   __ Push(R6);
   __ Push(R4);
 
   // R2: Smi-tagged arguments array length.
   PushArgumentsArray(assembler);
 
   const intptr_t kNumArgs = 3;
   __ CallRuntime(kInvokeClosureNoSuchMethodRuntimeEntry, kNumArgs);
   // noSuchMethod on closures always throws an error, so it will never return.
   __ brk(0);
@@ skipping 234 matching lines @@
   __ add(R7, SP, Operand(R7, UXTX, 3));  // R7 is Untagged.
   // R7: address of receiver.
   // Create a stub frame as we are pushing some objects on the stack before
   // calling into the runtime.
   __ EnterStubFrame();
   // Preserve IC data object and arguments descriptor array and
   // setup space on stack for result (target code object).
   __ Push(R4);  // Preserve arguments descriptor array.
   __ Push(R5);  // Preserve IC Data.
   // Setup space on stack for the result (target code object).
-  __ PushObject(Object::null_object());
+  __ Push(ZR);
   // Push call arguments.
   for (intptr_t i = 0; i < num_args; i++) {
     __ LoadFromOffset(TMP, R7, -i * kWordSize);
     __ Push(TMP);
   }
   // Pass IC data object.
   __ Push(R5);
   __ CallRuntime(handle_ic_miss, num_args + 1);
   // Remove the call arguments pushed earlier, including the IC data object.
   __ Drop(num_args + 1);
@@ skipping 210 matching lines @@
   __ LoadFieldFromOffset(CODE_REG, R0, Function::code_offset());
   __ LoadFieldFromOffset(R2, R0, Function::entry_point_offset());
   __ br(R2);
 }
 
 
 // R5: Contains an ICData.
 void StubCode::GenerateICCallBreakpointStub(Assembler* assembler) {
   __ EnterStubFrame();
   __ Push(R5);
-  __ PushObject(Object::null_object());  // Space for result.
+  __ Push(ZR);  // Space for result.
   __ CallRuntime(kBreakpointRuntimeHandlerRuntimeEntry, 0);
   __ Pop(CODE_REG);
   __ Pop(R5);
   __ LeaveStubFrame();
   __ LoadFieldFromOffset(R0, CODE_REG, Code::entry_point_offset());
   __ br(R0);
 }
 
 
 void StubCode::GenerateRuntimeCallBreakpointStub(Assembler* assembler) {
   __ EnterStubFrame();
-  __ PushObject(Object::null_object());  // Space for result.
+  __ Push(ZR);  // Space for result.
   __ CallRuntime(kBreakpointRuntimeHandlerRuntimeEntry, 0);
   __ Pop(CODE_REG);
   __ LeaveStubFrame();
   __ LoadFieldFromOffset(R0, CODE_REG, Code::entry_point_offset());
   __ br(R0);
 }
 
 // Called only from unoptimized code. All relevant registers have been saved.
 void StubCode::GenerateDebugStepCheckStub(
     Assembler* assembler) {
@@ skipping 160 matching lines @@
 }
 
 
 // Calls to the runtime to optimize the given function.
 // R6: function to be re-optimized.
 // R4: argument descriptor (preserved).
 void StubCode::GenerateOptimizeFunctionStub(Assembler* assembler) {
   __ EnterStubFrame();
   __ Push(R4);
   // Setup space on stack for the return value.
-  __ PushObject(Object::null_object());
+  __ Push(ZR);
   __ Push(R6);
   __ CallRuntime(kOptimizeInvokedFunctionRuntimeEntry, 1);
   __ Pop(R0);  // Discard argument.
   __ Pop(CODE_REG);  // Get Code object
   __ Pop(R4);  // Restore argument descriptor.
   __ LoadFieldFromOffset(R0, CODE_REG, Code::entry_point_offset());
   __ LeaveStubFrame();
   __ br(R0);
   __ brk(0);
 }
@@ skipping 265 matching lines @@
 
 // Called from switchable IC calls.
 //  R0: receiver
 //  R5: SingleTargetCache
 void StubCode::GenerateUnlinkedCallStub(Assembler* assembler) {
   __ NoMonomorphicCheckedEntry();
 
   __ EnterStubFrame();
   __ Push(R0);  // Preserve receiver.
 
-  __ PushObject(Object::null_object());  // Result.
-  __ Push(R0);                           // Arg0: Receiver
-  __ Push(R5);                           // Arg1: UnlinkedCall
+  __ Push(ZR);  // Result slot.
+  __ Push(R0);  // Arg0: Receiver
+  __ Push(R5);  // Arg1: UnlinkedCall
   __ CallRuntime(kUnlinkedCallRuntimeEntry, 2);
   __ Drop(2);
   __ Pop(R5);  // result = IC
 
   __ Pop(R0);  // Restore receiver.
   __ LeaveStubFrame();
 
   __ ldr(CODE_REG, Address(THR, Thread::ic_lookup_through_code_stub_offset()));
   __ ldr(R1, FieldAddress(CODE_REG, Code::checked_entry_point_offset()));
   __ br(R1);
@@ skipping 22 matching lines @@
   __ b(&miss, GT);
 
   __ ldr(R1, FieldAddress(R5, SingleTargetCache::entry_point_offset()));
   __ ldr(CODE_REG, FieldAddress(R5, SingleTargetCache::target_offset()));
   __ br(R1);
 
   __ Bind(&miss);
   __ EnterStubFrame();
   __ Push(R0);  // Preserve receiver.
 
-  __ PushObject(Object::null_object());  // Result.
-  __ Push(R0);                           // Arg0: Receiver
+  __ Push(ZR);  // Result slot.
+  __ Push(R0);  // Arg0: Receiver
   __ CallRuntime(kSingleTargetMissRuntimeEntry, 1);
   __ Drop(1);
   __ Pop(R5);  // result = IC
 
   __ Pop(R0);  // Restore receiver.
   __ LeaveStubFrame();
 
   __ ldr(CODE_REG, Address(THR, Thread::ic_lookup_through_code_stub_offset()));
   __ ldr(R1, FieldAddress(CODE_REG, Code::checked_entry_point_offset()));
   __ br(R1);
 }
 
 
 // Called from the monomorphic checked entry.
 //  R0: receiver
 void StubCode::GenerateMonomorphicMissStub(Assembler* assembler) {
   __ EnterStubFrame();
   __ Push(R0);  // Preserve receiver.
 
-  __ PushObject(Object::null_object());  // Result.
-  __ Push(R0);                           // Arg0: Receiver
+  __ Push(ZR);  // Result slot.
+  __ Push(R0);  // Arg0: Receiver
   __ CallRuntime(kMonomorphicMissRuntimeEntry, 1);
   __ Drop(1);
   __ Pop(R5);  // result = IC
 
   __ Pop(R0);  // Restore receiver.
   __ LeaveStubFrame();
 
   __ ldr(CODE_REG, Address(THR, Thread::ic_lookup_through_code_stub_offset()));
   __ ldr(R1, FieldAddress(CODE_REG, Code::checked_entry_point_offset()));
   __ br(R1);
 }
 
 
 void StubCode::GenerateFrameAwaitingMaterializationStub(Assembler* assembler) {
   __ brk(0);
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_ARM64