[sparkplug] Load undefined to accumulator in Prologue

Since we always call the out-of-line Prologue, we can preload the
accumulator in there with undefined instead of having to emit an
undefined load in every Sparkplug code header.

Change-Id: Ie0385316b0ee8bf96cd0069cda0496d05a4fb1eb
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2933144Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/master@{#74919}

src/baseline/arm/baseline-compiler-arm-inl.h

@@ -31,7 +31,11 @@ void BaselineCompiler::PrologueFillFrame() {
   // Inlined register frame fill
   interpreter::Register new_target_or_generator_register =
       bytecode_->incoming_new_target_or_generator_register();
-  __ LoadRoot(kInterpreterAccumulatorRegister, RootIndex::kUndefinedValue);
+  if (FLAG_debug_code) {
+    __ masm()->CompareRoot(kInterpreterAccumulatorRegister,
+                           RootIndex::kUndefinedValue);
+    __ masm()->Assert(eq, AbortReason::kUnexpectedValue);
+  }
   int register_count = bytecode_->register_count();
   // Magic value
   const int kLoopUnrollSize = 8;

src/baseline/arm64/baseline-compiler-arm64-inl.h

@@ -32,7 +32,11 @@ void BaselineCompiler::PrologueFillFrame() {
   // Inlined register frame fill
   interpreter::Register new_target_or_generator_register =
       bytecode_->incoming_new_target_or_generator_register();
-  __ LoadRoot(kInterpreterAccumulatorRegister, RootIndex::kUndefinedValue);
+  if (FLAG_debug_code) {
+    __ masm()->CompareRoot(kInterpreterAccumulatorRegister,
+                           RootIndex::kUndefinedValue);
+    __ masm()->Assert(eq, AbortReason::kUnexpectedValue);
+  }
   int register_count = bytecode_->register_count();
   // Magic value
   const int kLoopUnrollSize = 8;

src/baseline/ia32/baseline-compiler-ia32-inl.h

@@ -30,7 +30,11 @@ void BaselineCompiler::PrologueFillFrame() {
   // Inlined register frame fill
   interpreter::Register new_target_or_generator_register =
       bytecode_->incoming_new_target_or_generator_register();
-  __ LoadRoot(kInterpreterAccumulatorRegister, RootIndex::kUndefinedValue);
+  if (FLAG_debug_code) {
+    __ masm()->CompareRoot(kInterpreterAccumulatorRegister,
+                           RootIndex::kUndefinedValue);
+    __ masm()->Assert(equal, AbortReason::kUnexpectedValue);
+  }
   int register_count = bytecode_->register_count();
   // Magic value
   const int kLoopUnrollSize = 8;

src/baseline/x64/baseline-compiler-x64-inl.h

@@ -30,7 +30,11 @@ void BaselineCompiler::PrologueFillFrame() {
   // Inlined register frame fill
   interpreter::Register new_target_or_generator_register =
       bytecode_->incoming_new_target_or_generator_register();
-  __ LoadRoot(kInterpreterAccumulatorRegister, RootIndex::kUndefinedValue);
+  if (FLAG_debug_code) {
+    __ masm()->Cmp(kInterpreterAccumulatorRegister,
+                   isolate_->factory()->undefined_value());
+    __ masm()->Assert(equal, AbortReason::kUnexpectedValue);
+  }
   int register_count = bytecode_->register_count();
   // Magic value
   const int kLoopUnrollSize = 8;

src/builtins/arm/builtins-arm.cc

@@ -1154,6 +1154,7 @@ void Builtins::Generate_BaselineOutOfLinePrologue(MacroAssembler* masm) {
   }
 
   // Do "fast" return to the caller pc in lr.
+  __ LoadRoot(kInterpreterAccumulatorRegister, RootIndex::kUndefinedValue);
   __ Ret();
 
   __ bind(&has_optimized_code_or_marker);
@@ -1184,6 +1185,7 @@ void Builtins::Generate_BaselineOutOfLinePrologue(MacroAssembler* masm) {
     __ RecordComment("]");
   }
 
+  __ LoadRoot(kInterpreterAccumulatorRegister, RootIndex::kUndefinedValue);
   __ Ret();
 }
 

src/builtins/arm64/builtins-arm64.cc

@@ -1274,7 +1274,7 @@ void Builtins::Generate_BaselineOutOfLinePrologue(MacroAssembler* masm) {
       BaselineOutOfLinePrologueDescriptor::kJavaScriptCallArgCount);
   // We'll use the bytecode for both code age/OSR resetting, and pushing onto
   // the frame, so load it into a register.
-  Register bytecodeArray = descriptor.GetRegisterParameter(
+  Register bytecode_array = descriptor.GetRegisterParameter(
       BaselineOutOfLinePrologueDescriptor::kInterpreterBytecodeArray);
 
   // Reset code age and the OSR arming. The OSR field and BytecodeAgeOffset
@@ -1283,10 +1283,10 @@ void Builtins::Generate_BaselineOutOfLinePrologue(MacroAssembler* masm) {
   STATIC_ASSERT(BytecodeArray::kBytecodeAgeOffset ==
                 BytecodeArray::kOsrNestingLevelOffset + kCharSize);
   STATIC_ASSERT(BytecodeArray::kNoAgeBytecodeAge == 0);
-  __ Strh(wzr, FieldMemOperand(bytecodeArray,
+  __ Strh(wzr, FieldMemOperand(bytecode_array,
                                BytecodeArray::kOsrNestingLevelOffset));
 
-  __ Push(argc, bytecodeArray);
+  __ Push(argc, bytecode_array);
 
   // Baseline code frames store the feedback vector where interpreter would
   // store the bytecode offset.
@@ -1297,9 +1297,6 @@ void Builtins::Generate_BaselineOutOfLinePrologue(MacroAssembler* masm) {
   // Our stack is currently aligned. We have have to push something along with
   // the feedback vector to keep it that way -- we may as well start
   // initialising the register frame.
-  // TODO(v8:11429,leszeks): Consider guaranteeing that this call leaves
-  // `undefined` in the accumulator register, to skip the load in the baseline
-  // code.
   __ LoadRoot(kInterpreterAccumulatorRegister, RootIndex::kUndefinedValue);
   __ Push(feedback_vector, kInterpreterAccumulatorRegister);
   __ RecordComment("]");
@@ -1326,7 +1323,11 @@ void Builtins::Generate_BaselineOutOfLinePrologue(MacroAssembler* masm) {
   }
 
   // Do "fast" return to the caller pc in lr.
-  // TODO(v8:11429): Document this frame setup better.
+  if (FLAG_debug_code) {
+    // The accumulator should already be "undefined", we don't have to load it.
+    __ CompareRoot(kInterpreterAccumulatorRegister, RootIndex::kUndefinedValue);
+    __ Assert(eq, AbortReason::kUnexpectedValue);
+  }
   __ Ret();
 
   __ bind(&has_optimized_code_or_marker);
@@ -1355,6 +1356,7 @@ void Builtins::Generate_BaselineOutOfLinePrologue(MacroAssembler* masm) {
     __ Pop(new_target, padreg);
     __ RecordComment("]");
   }
+  __ LoadRoot(kInterpreterAccumulatorRegister, RootIndex::kUndefinedValue);
   __ Ret();
 }
 

src/builtins/ia32/builtins-ia32.cc

@@ -1744,6 +1744,7 @@ void Builtins::Generate_BaselineOutOfLinePrologue(MacroAssembler* masm) {
   // Push the return address back onto the stack for return.
   __ PushReturnAddressFrom(return_address, scratch);
   // Return to caller pushed pc, without any frame teardown.
+  __ LoadRoot(kInterpreterAccumulatorRegister, RootIndex::kUndefinedValue);
   __ Ret();
 
   __ bind(&has_optimized_code_or_marker);
@@ -1778,6 +1779,7 @@ void Builtins::Generate_BaselineOutOfLinePrologue(MacroAssembler* masm) {
     }
 
     // Return to caller pushed pc, without any frame teardown.
+    __ LoadRoot(kInterpreterAccumulatorRegister, RootIndex::kUndefinedValue);
     __ Ret();
     __ RecordComment("]");
   }

src/builtins/x64/builtins-x64.cc

@@ -1726,6 +1726,7 @@ void Builtins::Generate_BaselineOutOfLinePrologue(MacroAssembler* masm) {
   // Push the return address back onto the stack for return.
   __ PushReturnAddressFrom(return_address);
   // Return to caller pushed pc, without any frame teardown.
+  __ LoadRoot(kInterpreterAccumulatorRegister, RootIndex::kUndefinedValue);
   __ Ret();
 
   __ bind(&has_optimized_code_or_marker);
@@ -1760,6 +1761,7 @@ void Builtins::Generate_BaselineOutOfLinePrologue(MacroAssembler* masm) {
     }
 
     // Return to caller pushed pc, without any frame teardown.
+    __ LoadRoot(kInterpreterAccumulatorRegister, RootIndex::kUndefinedValue);
     __ Ret();
     __ RecordComment("]");
   }