[mips][builtins] Avoid reloading undefined value in InterpreterEntryTrampoline

Port: 40c0f84a

Bug: v8:9771
Change-Id: Icbe4e3450bb6ef7242804ca9d7f46cb6f1aed40c
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2539538
Auto-Submit: Liu yu <liuyu@loongson.cn>
Reviewed-by: Zhao Jiazhong <zhaojiazhong-hf@loongson.cn>
Commit-Queue: Zhao Jiazhong <zhaojiazhong-hf@loongson.cn>
Cr-Commit-Position: refs/heads/master@{#71336}

src/builtins/mips/builtins-mips.cc

@@ -1061,11 +1061,11 @@ 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(t1, RootIndex::kUndefinedValue);
+    __ LoadRoot(kInterpreterAccumulatorRegister, RootIndex::kUndefinedValue);
     __ Branch(&loop_check);
     __ bind(&loop_header);
     // TODO(rmcilroy): Consider doing more than one push per loop iteration.
-    __ push(t1);
+    __ push(kInterpreterAccumulatorRegister);
     // Continue loop if not done.
     __ bind(&loop_check);
     __ Subu(t0, t0, Operand(kPointerSize));
@@ -1091,8 +1091,7 @@ void Builtins::Generate_InterpreterEntryTrampoline(MacroAssembler* masm) {
   __ Branch(&stack_check_interrupt, lo, sp, Operand(a2));
   __ bind(&after_stack_check_interrupt);
 
-  // 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/mips64/builtins-mips64.cc

@@ -1077,11 +1077,11 @@ 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(a5, RootIndex::kUndefinedValue);
+    __ LoadRoot(kInterpreterAccumulatorRegister, RootIndex::kUndefinedValue);
     __ Branch(&loop_check);
     __ bind(&loop_header);
     // TODO(rmcilroy): Consider doing more than one push per loop iteration.
-    __ push(a5);
+    __ push(kInterpreterAccumulatorRegister);
     // Continue loop if not done.
     __ bind(&loop_check);
     __ Dsubu(a4, a4, Operand(kPointerSize));
@@ -1107,8 +1107,7 @@ void Builtins::Generate_InterpreterEntryTrampoline(MacroAssembler* masm) {
   __ Branch(&stack_check_interrupt, lo, sp, Operand(a5));
   __ bind(&after_stack_check_interrupt);
 
-  // Load accumulator as 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.