Remove Value<> boxing from struct fields

Author: nunoplopes

cpp2rust/converter/converter.cpp

@@ -1171,7 +1171,6 @@ void Converter::EmitConstructorFieldInits(clang::CXXConstructorDecl *decl) {
 
   for (const auto *field : record_decl->fields()) {
     auto field_name = GetNamedDeclAsString(field);
-    auto field_type = field->getType();
     const clang::CXXCtorInitializer *ctor_initializer = nullptr;
     for (const auto *init : definition->inits()) {
       if (init->isMemberInitializer() && init->getMember() == field) {
@@ -1180,15 +1179,9 @@ void Converter::EmitConstructorFieldInits(clang::CXXConstructorDecl *decl) {
       }
     }
 
-    if (ctor_initializer) {
-      StrCat(field_name, token::kColon);
-      ConvertVarInit(field_type, ctor_initializer->getInit());
-    } else if (auto *init = field->getInClassInitializer()) {
-      StrCat(field_name, token::kColon);
-      ConvertVarInit(field_type, init);
-    } else {
-      StrCat(field_name, token::kColon, GetDefaultAsString(field_type));
-    }
+    StrCat(field_name, token::kColon);
+    ConvertFieldInit(field, ctor_initializer ? ctor_initializer->getInit()
+                                             : field->getInClassInitializer());
     StrCat(token::kComma);
   }
 }
@@ -2444,7 +2437,9 @@ bool Converter::VisitImplicitCastExpr(clang::ImplicitCastExpr *expr) {
   case clang::CastKind::CK_LValueToRValue: {
     PushExprKind push(*this, ExprKind::RValue);
     Convert(sub_expr);
-    SetValueFreshness(type);
+    if (!isFresh()) {
+      SetValueFreshness(type);
+    }
     break;
   }
   case clang::CastKind::CK_ArrayToPointerDecay: {
@@ -3398,7 +3393,7 @@ bool Converter::VisitInitListExpr(clang::InitListExpr *expr) {
     int i = 0;
     for (const auto *field : record->fields()) {
       StrCat(GetNamedDeclAsString(field), token::kColon);
-      ConvertVarInit(field->getType(), expr->getInit(i++));
+      ConvertFieldInit(field, expr->getInit(i++));
       StrCat(token::kComma);
     }
   } else {
@@ -4665,15 +4660,20 @@ void Converter::EmitDefaultStructLiteral(const clang::RecordDecl *decl) {
   PushBrace brace(*this);
   for (auto *field : decl->fields()) {
     StrCat(GetNamedDeclAsString(field), token::kColon);
-    if (auto *init = field->getInClassInitializer()) {
-      ConvertVarInit(field->getType(), init);
-    } else {
-      StrCat(GetDefaultAsString(field->getType()));
-    }
+    ConvertFieldInit(field, field->getInClassInitializer());
     StrCat(token::kComma);
   }
 }
 
+void Converter::ConvertFieldInit(const clang::FieldDecl *field,
+                                 clang::Expr *init) {
+  if (init) {
+    ConvertVarInit(field->getType(), init);
+  } else {
+    StrCat(GetDefaultAsString(field->getType()));
+  }
+}
+
 void Converter::AddByteReprTrait(const clang::RecordDecl *decl) {}
 
 void Converter::ConvertUnsignedArithBinaryOperator(clang::BinaryOperator *op,
@@ -4838,8 +4838,16 @@ void Converter::PlaceholderCtx::dump() const {
                << ", materialize_idx: " << materialize_idx << '\n';
 }
 
+std::string Converter::ConvertTake(clang::Expr *arg) {
+  return std::format("std::mem::take(&mut {})", ConvertLValue(arg));
+}
+
 std::string Converter::ConvertPlaceholder(clang::Expr *expr, clang::Expr *arg,
                                           const PlaceholderCtx &ph_ctx) {
+  if (auto it = hoisted_exprs_.find(arg); it != hoisted_exprs_.end()) {
+    return it->second;
+  }
+
   if (arg->getType()->isFunctionPointerType()) {
     return ConvertFnPtrPlaceholder(arg);
   }
@@ -4907,9 +4915,9 @@ std::string Converter::ConvertPlaceholder(clang::Expr *expr, clang::Expr *arg,
       }
       return ConvertFreshRValue(arg);
     }
-    auto lvalue = ConvertLValue(arg);
+    auto str = ConvertTake(arg);
     SetFresh();
-    return std::format("std::mem::take(&mut {})", std::move(lvalue));
+    return str;
   }
 
   if (ph_ctx.access == TranslationRule::Access::kMove) {

cpp2rust/converter/converter.h

@@ -340,6 +340,9 @@ class Converter : public clang::RecursiveASTVisitor<Converter> {
   std::string ConvertFnPtrCallee(clang::Expr *arg);
   virtual std::string ConvertFnPtrPlaceholder(clang::Expr *arg);
 
+  // Moves the value of the lvalue arg out, leaving a default value behind.
+  virtual std::string ConvertTake(clang::Expr *arg);
+
   // Option<fn> implements Copy
   virtual bool FunctionPointerImplementsCopy() const { return true; }
 
@@ -597,6 +600,11 @@ class Converter : public clang::RecursiveASTVisitor<Converter> {
 
   virtual void ConvertVarInit(clang::QualType qual_type, clang::Expr *expr);
 
+  // The initial value of a field of a struct: `init`, or the default value
+  // if null.
+  virtual void ConvertFieldInit(const clang::FieldDecl *field,
+                                clang::Expr *init);
+
   virtual void ConvertUnsignedArithOperand(clang::Expr *expr,
                                            clang::QualType type);
 
@@ -696,7 +704,7 @@ class Converter : public clang::RecursiveASTVisitor<Converter> {
                                 unsigned num_args = 0,
                                 TempMaterializationCtx *ctx = nullptr);
 
-  std::string
+  virtual std::string
   ConvertIRFragment(const std::vector<TranslationRule::BodyFragment> &fragments,
                     clang::Expr *expr, clang::Expr **args, unsigned num_args,
                     TempMaterializationCtx *ctx);
@@ -760,6 +768,10 @@ class Converter : public clang::RecursiveASTVisitor<Converter> {
   };
 
   std::string ufcs_receiver_;
+
+  // Expressions that were evaluated into local variables ahead of the
+  // expression that contains them, and the names of these variables.
+  std::unordered_map<const clang::Expr *, std::string> hoisted_exprs_;
   bool in_const_initializer_ = false;
   std::optional<bool> autoref_mut_;
   bool suppress_iterator_clone_ = false;