[vm/bytecode] Fix removal of empty scopes in local variable info

alexmarkov · commit-bot@chromium.org · commit 730d2c6c6ccd · 2019-07-22T21:54:49.000Z
Even if a scope doesn't have variables, it may define a context level different from enclosing scope. As debugger needs to know context level at any point, bytecode generator should not elide such scopes. Change-Id: I2f97deae55285b758f91aee852338432dcddf373 Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/109898 Reviewed-by: Régis Crelier <regis@google.com> Reviewed-by: Ryan Macnak <rmacnak@google.com> Commit-Queue: Alexander Markov <alexmarkov@google.com>
diff --git a/pkg/vm/lib/bytecode/local_variable_table.dart b/pkg/vm/lib/bytecode/local_variable_table.dart
@@ -51,7 +51,7 @@ class Scope extends LocalVariableEntry {
   }
 
   Scope.readContents(BufferedReader reader, int startPC) : super(startPC) {
-    endPC = startPC = reader.readPackedUInt30();
+    endPC = startPC + reader.readPackedUInt30();
     contextLevel = reader.readSLEB128();
     position = reader.readPackedUInt30() - 1;
     endPosition = reader.readPackedUInt30() - 1;
@@ -152,7 +152,9 @@ class LocalVariableTable {
     final scope = activeScopes.removeLast();
     scope.endPC = pc;
     scope.endPosition = endPosition;
-    if (scope.variables.isEmpty) {
+    if (scope.variables.isEmpty &&
+        activeScopes.isNotEmpty &&
+        scope.contextLevel == activeScopes.last.contextLevel) {
       scopes.remove(scope);
     }
   }

Original file line number	Diff line number	Diff line change
`@@ -51,7 +51,7 @@ class Scope extends LocalVariableEntry {`
`51`	`51`	`}`
`52`	`52`
`53`	`53`	`Scope.readContents(BufferedReader reader, int startPC) : super(startPC) {`
`54`		`- endPC = startPC = reader.readPackedUInt30();`
	`54`	`+ endPC = startPC + reader.readPackedUInt30();`
`55`	`55`	`contextLevel = reader.readSLEB128();`
`56`	`56`	`position = reader.readPackedUInt30() - 1;`
`57`	`57`	`endPosition = reader.readPackedUInt30() - 1;`
`@@ -152,7 +152,9 @@ class LocalVariableTable {`
`152`	`152`	`final scope = activeScopes.removeLast();`
`153`	`153`	`scope.endPC = pc;`
`154`	`154`	`scope.endPosition = endPosition;`
`155`		`- if (scope.variables.isEmpty) {`
	`155`	`+ if (scope.variables.isEmpty &&`
	`156`	`+ activeScopes.isNotEmpty &&`
	`157`	`+ scope.contextLevel == activeScopes.last.contextLevel) {`
`156`	`158`	`scopes.remove(scope);`
`157`	`159`	`}`
`158`	`160`	`}`