[cfe] Avoid lowering for LocalIncDec

This changes the encoding of LocalPostIncDec (now called LocalIncDec) to avoid lowering during body building.

To achieve this, the inference for VariableGet and VariableSet have been refactoring to allow for reuse through LocalIncDec. Similar refactorings have been done for StaticGet/Set/IncDec and SuperPropertyGet/PropertySet/IncDec.

TEST=existing

Change-Id: I84522c510520cadf8ade95345d724ffbf2816ff5
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/447180
Reviewed-by: Tess Strickland <[email protected]>
Reviewed-by: Chloe Stefantsova <[email protected]>
Commit-Queue: Johnni Winther <[email protected]>

Author: johnniwinther

pkg/front_end/lib/src/kernel/body_builder.dart

@@ -3220,14 +3220,19 @@ class BodyBuilder extends StackListenerImpl
     ]));
   }
 
-  /// Helper method to create a [VariableGet] of the [variable] using
-  /// [charOffset] as the file offset.
   @override
-  VariableGet createVariableGet(VariableDeclaration variable, int charOffset) {
+  void registerVariableRead(VariableDeclaration variable) {
     if (!(variable as VariableDeclarationImpl).isLocalFunction &&
         !variable.isWildcard) {
       typeInferrer.assignedVariables.read(variable);
     }
+  }
+
+  /// Helper method to create a [VariableGet] of the [variable] using
+  /// [charOffset] as the file offset.
+  @override
+  VariableGet createVariableGet(VariableDeclaration variable, int charOffset) {
+    registerVariableRead(variable);
     return new VariableGet(variable)..fileOffset = charOffset;
   }
 

pkg/front_end/lib/src/kernel/expression_generator.dart

@@ -318,9 +318,9 @@ class VariableUseGenerator extends Generator {
   final VariableDeclaration variable;
 
   VariableUseGenerator(
-      ExpressionGeneratorHelper helper, Token token, this.variable)
+      ExpressionGeneratorHelper helper, Token nameToken, this.variable)
       : assert(variable.isAssignable, 'Variable $variable is not assignable'),
-        super(helper, token);
+        super(helper, nameToken);
 
   @override
   // Coverage-ignore(suite): Not run.
@@ -329,6 +329,8 @@ class VariableUseGenerator extends Generator {
   @override
   String get _plainNameForRead => variable.name!;
 
+  int get _nameOffset => fileOffset;
+
   @override
   Expression buildSimpleRead() {
     return _createRead();
@@ -343,11 +345,15 @@ class VariableUseGenerator extends Generator {
     return _createWrite(fileOffset, value);
   }
 
-  Expression _createWrite(int offset, Expression value) {
+  void _checkAssignment(int offset) {
     if (_helper.isDeclaredInEnclosingCase(variable)) {
       _helper.addProblem(
           codePatternVariableAssignmentInsideGuard, offset, noLength);
     }
+  }
+
+  Expression _createWrite(int offset, Expression value) {
+    _checkAssignment(offset);
     _helper.registerVariableAssignment(variable);
     return new VariableSet(variable, value)..fileOffset = offset;
   }
@@ -372,9 +378,36 @@ class VariableUseGenerator extends Generator {
     return _createWrite(fileOffset, binary);
   }
 
+  Expression _buildPrePostfixIncrement(Name binaryOperator,
+      {required int operatorOffset,
+      required bool forEffect,
+      required bool isPost}) {
+    _checkAssignment(_nameOffset);
+    _helper.registerVariableRead(variable);
+    _helper.registerVariableAssignment(variable);
+    return new LocalIncDec(
+        variable: variable as VariableDeclarationImpl,
+        forEffect: forEffect,
+        isPost: isPost,
+        isInc: binaryOperator == plusName,
+        nameOffset: _nameOffset,
+        operatorOffset: operatorOffset)
+      ..fileOffset = _nameOffset;
+  }
+
+  @override
+  Expression buildPrefixIncrement(Name binaryOperator,
+      {required int operatorOffset, bool voidContext = false}) {
+    return _buildPrePostfixIncrement(binaryOperator,
+        operatorOffset: operatorOffset, forEffect: voidContext, isPost: false);
+  }
+
   @override
   Expression buildPostfixIncrement(Name binaryOperator,
       {required int operatorOffset, bool voidContext = false}) {
+    return _buildPrePostfixIncrement(binaryOperator,
+        operatorOffset: operatorOffset, forEffect: voidContext, isPost: true);
+/*      
     Expression value = _forest.createIntLiteral(operatorOffset, 1);
     if (voidContext) {
       return buildCompoundAssignment(binaryOperator, value,
@@ -388,7 +421,7 @@ class VariableUseGenerator extends Generator {
         _helper.createVariableGet(read, fileOffset), binaryOperator, value);
     VariableDeclarationImpl write = _helper.createVariableDeclarationForValue(
         _createWrite(operatorOffset, binary));
-    return new LocalPostIncDec(read, write)..fileOffset = operatorOffset;
+    return new LocalIncDec(read, write)..fileOffset = operatorOffset;*/
   }
 
   @override

pkg/front_end/lib/src/kernel/expression_generator_helper.dart

@@ -169,6 +169,11 @@ abstract class ExpressionGeneratorHelper implements InferenceHelper {
   /// offset of the created node.
   Expression createVariableGet(VariableDeclaration variable, int charOffset);
 
+  /// Registers that [variable] is read from.
+  ///
+  /// This is needed for type promotion.
+  void registerVariableRead(VariableDeclaration variable);
+
   /// Registers that [variable] is assigned to.
   ///
   /// This is needed for type promotion.

pkg/front_end/lib/src/kernel/internal_ast.dart

@@ -1907,28 +1907,63 @@ class ExtensionIncDec extends InternalExpression {
 ///
 ///     let v1 = a in let v2 = a = v1 + 1 in v1
 ///
-class LocalPostIncDec extends InternalExpression {
-  /// The expression that reads the local variable.
-  VariableDeclarationImpl read;
+class LocalIncDec extends InternalExpression {
+  /// The accessed variable.
+  final VariableDeclarationImpl variable;
 
-  /// The expression that writes the result of the binary operation to the
-  /// local variable.
-  VariableDeclarationImpl write;
+  /// `true` if the inc/dec is a postfix expression, i.e. of the form `a++` as
+  /// opposed the prefix expression `++a`.
+  final bool isPost;
 
-  LocalPostIncDec(this.read, this.write) {
-    read.parent = this;
-    write.parent = this;
-  }
+  /// If `true` the assignment is need for its effect and not for its value.
+  final bool forEffect;
+
+  /// `true` if this is an post increment, i.e. `a++` as opposed to `a--`.
+  final bool isInc;
+
+  /// The file offset of the name of the getter/setter, i.e. `a` in `a++`.
+  final int nameOffset;
+
+  /// The file offset of the `++` or `--` operator.
+  final int operatorOffset;
+
+  LocalIncDec(
+      {required this.variable,
+      required this.forEffect,
+      required this.isPost,
+      required this.isInc,
+      required this.nameOffset,
+      required this.operatorOffset});
 
   @override
   ExpressionInferenceResult acceptInference(
       InferenceVisitorImpl visitor, DartType typeContext) {
-    return visitor.visitLocalPostIncDec(this, typeContext);
+    return visitor.visitLocalIncDec(this, typeContext);
+  }
+
+  @override
+  // Coverage-ignore(suite): Not run.
+  void toTextInternal(AstPrinter printer) {
+    if (!isPost) {
+      if (isInc) {
+        printer.write('++');
+      } else {
+        printer.write('--');
+      }
+    }
+    printer.write(variable.name!);
+    if (isPost) {
+      if (isInc) {
+        printer.write('++');
+      } else {
+        printer.write('--');
+      }
+    }
   }
 
   @override
   String toString() {
-    return "LocalPostIncDec(${toStringInternal()})";
+    return "LocalIncDec(${toStringInternal()})";
   }
 }