[builtins] Avoid reloading undefined value in InterpreterEntryTrampoline

Since we were already loading the undefined value a few lines above,
we could avoid loading it again.

Bug: v8:9771
Change-Id: Id05a77494c06a212612a365b5c0dcba4803ba756
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1817609
Commit-Queue: Santiago Aboy Solanes <solanes@chromium.org>
Reviewed-by: Dan Elphick <delphick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#63935}

src/builtins/arm/builtins-arm.cc

@@ -1138,11 +1138,11 @@ void Builtins::Generate_InterpreterEntryTrampoline(MacroAssembler* masm) {
     // If ok, push undefined as the initial value for all register file entries.
     Label loop_header;
     Label loop_check;
-    __ LoadRoot(r9, RootIndex::kUndefinedValue);
+    __ LoadRoot(kInterpreterAccumulatorRegister, RootIndex::kUndefinedValue);
     __ b(&loop_check, al);
     __ bind(&loop_header);
     // TODO(rmcilroy): Consider doing more than one push per loop iteration.
-    __ push(r9);
+    __ push(kInterpreterAccumulatorRegister);
     // Continue loop if not done.
     __ bind(&loop_check);
     __ sub(r4, r4, Operand(kPointerSize), SetCC);
@@ -1157,8 +1157,7 @@ void Builtins::Generate_InterpreterEntryTrampoline(MacroAssembler* masm) {
   __ cmp(r9, Operand::Zero());
   __ str(r3, MemOperand(fp, r9, LSL, kPointerSizeLog2), ne);
 
-  // Load accumulator with undefined.
-  __ LoadRoot(kInterpreterAccumulatorRegister, RootIndex::kUndefinedValue);
+  // The accumulator is already loaded with undefined.
 
   // Load the dispatch table into a register and dispatch to the bytecode
   // handler at the current bytecode offset.

src/builtins/arm64/builtins-arm64.cc

@@ -1270,13 +1270,13 @@ void Builtins::Generate_InterpreterEntryTrampoline(MacroAssembler* masm) {
     // Note: there should always be at least one stack slot for the return
     // register in the register file.
     Label loop_header;
-    __ LoadRoot(x10, RootIndex::kUndefinedValue);
+    __ LoadRoot(kInterpreterAccumulatorRegister, RootIndex::kUndefinedValue);
     __ Lsr(x11, x11, kSystemPointerSizeLog2);
     // Round up the number of registers to a multiple of 2, to align the stack
     // to 16 bytes.
     __ Add(x11, x11, 1);
     __ Bic(x11, x11, 1);
-    __ PushMultipleTimes(x10, x11);
+    __ PushMultipleTimes(kInterpreterAccumulatorRegister, x11);
     __ Bind(&loop_header);
   }
 
@@ -1291,8 +1291,7 @@ void Builtins::Generate_InterpreterEntryTrampoline(MacroAssembler* masm) {
   __ Str(x3, MemOperand(fp, x10, LSL, kSystemPointerSizeLog2));
   __ Bind(&no_incoming_new_target_or_generator_register);
 
-  // Load accumulator with undefined.
-  __ LoadRoot(kInterpreterAccumulatorRegister, RootIndex::kUndefinedValue);
+  // The accumulator is already loaded with undefined.
 
   // Load the dispatch table into a register and dispatch to the bytecode
   // handler at the current bytecode offset.

src/builtins/x64/builtins-x64.cc

@@ -1154,11 +1154,11 @@ void Builtins::Generate_InterpreterEntryTrampoline(MacroAssembler* masm) {
     // If ok, push undefined as the initial value for all register file entries.
     Label loop_header;
     Label loop_check;
-    __ LoadRoot(rax, RootIndex::kUndefinedValue);
+    __ LoadRoot(kInterpreterAccumulatorRegister, RootIndex::kUndefinedValue);
     __ j(always, &loop_check, Label::kNear);
     __ bind(&loop_header);
     // TODO(rmcilroy): Consider doing more than one push per loop iteration.
-    __ Push(rax);
+    __ Push(kInterpreterAccumulatorRegister);
     // Continue loop if not done.
     __ bind(&loop_check);
     __ subq(rcx, Immediate(kSystemPointerSize));
@@ -1169,16 +1169,15 @@ void Builtins::Generate_InterpreterEntryTrampoline(MacroAssembler* masm) {
   // register, initialize it with incoming value which was passed in rdx.
   Label no_incoming_new_target_or_generator_register;
   __ movsxlq(
-      rax,
+      rcx,
       FieldOperand(kInterpreterBytecodeArrayRegister,
                    BytecodeArray::kIncomingNewTargetOrGeneratorRegisterOffset));
-  __ testl(rax, rax);
+  __ testl(rcx, rcx);
   __ j(zero, &no_incoming_new_target_or_generator_register, Label::kNear);
-  __ movq(Operand(rbp, rax, times_system_pointer_size, 0), rdx);
+  __ movq(Operand(rbp, rcx, times_system_pointer_size, 0), rdx);
   __ bind(&no_incoming_new_target_or_generator_register);
 
-  // Load accumulator with undefined.
-  __ LoadRoot(kInterpreterAccumulatorRegister, RootIndex::kUndefinedValue);
+  // The accumulator is already loaded with undefined.
 
   // Load the dispatch table into a register and dispatch to the bytecode
   // handler at the current bytecode offset.