[torque] avoid using nullptr_t for BottomOffset

This avoids a warning by clang-tidy's modernize-use-nullptr.

Bug: v8:10488
Change-Id: I2820c7e5223101c5e3f7122d2a6a3526d36851e7
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2218063Reviewed-by: Zhi An Ng <zhin@chromium.org>
Commit-Queue: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68065}

src/torque/cfg.h

@@ -63,7 +63,7 @@ class Block {
 
     DCHECK_EQ(input_definitions_->Size(), input_definitions.Size());
     bool changed = false;
-    for (BottomOffset i = 0; i < input_definitions.AboveTop(); ++i) {
+    for (BottomOffset i = {0}; i < input_definitions.AboveTop(); ++i) {
       auto& current = input_definitions_->Peek(i);
       auto& input = input_definitions.Peek(i);
       if (current == input) continue;

src/torque/csa-generator.cc

@@ -16,7 +16,7 @@ namespace torque {
 
 base::Optional<Stack<std::string>> CSAGenerator::EmitGraph(
     Stack<std::string> parameters) {
-  for (BottomOffset i = 0; i < parameters.AboveTop(); ++i) {
+  for (BottomOffset i = {0}; i < parameters.AboveTop(); ++i) {
     SetDefinitionVariable(DefinitionLocation::Parameter(i.offset),
                           parameters.Peek(i));
   }
@@ -27,7 +27,7 @@ base::Optional<Stack<std::string>> CSAGenerator::EmitGraph(
     out() << "  compiler::CodeAssemblerParameterizedLabel<";
     bool first = true;
     DCHECK_EQ(block->InputTypes().Size(), block->InputDefinitions().Size());
-    for (BottomOffset i = 0; i < block->InputTypes().AboveTop(); ++i) {
+    for (BottomOffset i = {0}; i < block->InputTypes().AboveTop(); ++i) {
       if (block->InputDefinitions().Peek(i).IsPhiFromBlock(block)) {
         if (!first) out() << ", ";
         out() << block->InputTypes().Peek(i)->GetGeneratedTNodeTypeName();
@@ -70,7 +70,7 @@ Stack<std::string> CSAGenerator::EmitBlock(const Block* block) {
   Stack<std::string> stack;
   std::stringstream phi_names;
 
-  for (BottomOffset i = 0; i < block->InputTypes().AboveTop(); ++i) {
+  for (BottomOffset i = {0}; i < block->InputTypes().AboveTop(); ++i) {
     const auto& def = block->InputDefinitions().Peek(i);
     stack.Push(DefinitionToVariable(def));
     if (def.IsPhiFromBlock(block)) {
@@ -468,7 +468,7 @@ void CSAGenerator::EmitInstruction(
 
     const auto& input_definitions =
         (*instruction.return_continuation)->InputDefinitions();
-    for (BottomOffset i = 0; i < input_definitions.AboveTop(); ++i) {
+    for (BottomOffset i = {0}; i < input_definitions.AboveTop(); ++i) {
       if (input_definitions.Peek(i).IsPhiFromBlock(
               *instruction.return_continuation)) {
         out() << ", "
@@ -487,7 +487,7 @@ void CSAGenerator::EmitInstruction(
     const auto& label_definitions =
         instruction.label_blocks[l]->InputDefinitions();
 
-    BottomOffset i = 0;
+    BottomOffset i = {0};
     for (; i < stack->AboveTop(); ++i) {
       if (label_definitions.Peek(i).IsPhiFromBlock(
               instruction.label_blocks[l])) {
@@ -630,7 +630,7 @@ void CSAGenerator::PostCallableExceptionPreparation(
 
     DCHECK_EQ(stack->Size() + 1, (*catch_block)->InputDefinitions().Size());
     const auto& input_definitions = (*catch_block)->InputDefinitions();
-    for (BottomOffset i = 0; i < input_definitions.AboveTop(); ++i) {
+    for (BottomOffset i = {0}; i < input_definitions.AboveTop(); ++i) {
       if (input_definitions.Peek(i).IsPhiFromBlock(*catch_block)) {
         if (i < stack->AboveTop()) {
           out() << ", " << stack->Peek(i);
@@ -713,7 +713,7 @@ void CSAGenerator::EmitInstruction(const BranchInstruction& instruction,
   const auto& true_definitions = instruction.if_true->InputDefinitions();
   DCHECK_EQ(stack->Size(), true_definitions.Size());
   bool first = true;
-  for (BottomOffset i = 0; i < stack->AboveTop(); ++i) {
+  for (BottomOffset i = {0}; i < stack->AboveTop(); ++i) {
     if (true_definitions.Peek(i).IsPhiFromBlock(instruction.if_true)) {
       if (!first) out() << ", ";
       out() << stack->Peek(i);
@@ -726,7 +726,7 @@ void CSAGenerator::EmitInstruction(const BranchInstruction& instruction,
   const auto& false_definitions = instruction.if_false->InputDefinitions();
   DCHECK_EQ(stack->Size(), false_definitions.Size());
   first = true;
-  for (BottomOffset i = 0; i < stack->AboveTop(); ++i) {
+  for (BottomOffset i = {0}; i < stack->AboveTop(); ++i) {
     if (false_definitions.Peek(i).IsPhiFromBlock(instruction.if_false)) {
       if (!first) out() << ", ";
       out() << stack->Peek(i);
@@ -744,7 +744,7 @@ void CSAGenerator::EmitInstruction(
 
   const auto& true_definitions = instruction.if_true->InputDefinitions();
   DCHECK_EQ(stack->Size(), true_definitions.Size());
-  for (BottomOffset i = 0; i < stack->AboveTop(); ++i) {
+  for (BottomOffset i = {0}; i < stack->AboveTop(); ++i) {
     if (true_definitions.Peek(i).IsPhiFromBlock(instruction.if_true)) {
       out() << ", " << stack->Peek(i);
     }
@@ -756,7 +756,7 @@ void CSAGenerator::EmitInstruction(
 
   const auto& false_definitions = instruction.if_false->InputDefinitions();
   DCHECK_EQ(stack->Size(), false_definitions.Size());
-  for (BottomOffset i = 0; i < stack->AboveTop(); ++i) {
+  for (BottomOffset i = {0}; i < stack->AboveTop(); ++i) {
     if (false_definitions.Peek(i).IsPhiFromBlock(instruction.if_false)) {
       out() << ", " << stack->Peek(i);
     }
@@ -772,7 +772,7 @@ void CSAGenerator::EmitInstruction(const GotoInstruction& instruction,
   const auto& destination_definitions =
       instruction.destination->InputDefinitions();
   DCHECK_EQ(stack->Size(), destination_definitions.Size());
-  for (BottomOffset i = 0; i < stack->AboveTop(); ++i) {
+  for (BottomOffset i = {0}; i < stack->AboveTop(); ++i) {
     if (destination_definitions.Peek(i).IsPhiFromBlock(
             instruction.destination)) {
       out() << ", " << stack->Peek(i);

src/torque/utils.h

@@ -172,9 +172,7 @@ void PrintCommaSeparatedList(std::ostream& os, const T& list) {
 
 struct BottomOffset {
   size_t offset;
-  BottomOffset(std::nullptr_t zero = 0)  // NOLINT(runtime/explicit)
-      : offset(0) {}
-  explicit BottomOffset(std::size_t offset) : offset(offset) {}
+
   BottomOffset& operator=(std::size_t offset) {
     this->offset = offset;
     return *this;