Force ctxt allocation in eval scopes.

This is another attempt at solving v8:5736; the previous one (r 41723)
regressed code load.

BUG=v8:5736
R=adamk@chromium.org

Review-Url: https://codereview.chromium.org/2583163002
Cr-Commit-Position: refs/heads/master@{#42049}

src/ast/scopes.cc

@@ -1178,7 +1178,10 @@ bool Scope::AllowsLazyParsingWithoutUnresolvedVariables(
   // the parse, since context allocation of those variables is already
   // guaranteed to be correct.
   for (const Scope* s = this; s != outer; s = s->outer_scope_) {
-    if (s->is_eval_scope()) return false;
+    // Eval forces context allocation on all outer scopes, so we don't need to
+    // look at those scopes. Sloppy eval makes top-level non-lexical variables
+    // dynamic, whereas strict-mode requires context allocation.
+    if (s->is_eval_scope()) return is_sloppy(s->language_mode());
     // Catch scopes force context allocation of all variables.
     if (s->is_catch_scope()) continue;
     // With scopes do not introduce variables that need allocation.
@@ -1887,7 +1890,10 @@ bool Scope::MustAllocateInContext(Variable* var) {
   if (has_forced_context_allocation()) return true;
   if (var->mode() == TEMPORARY) return false;
   if (is_catch_scope()) return true;
-  if (is_script_scope() && IsLexicalVariableMode(var->mode())) return true;
+  if ((is_script_scope() || is_eval_scope()) &&
+      IsLexicalVariableMode(var->mode())) {
+    return true;
+  }
   return var->has_forced_context_allocation() || inner_scope_calls_eval_;
 }
 

test/mjsunit/regress/regress-5736.js

@@ -24,3 +24,11 @@ assertEquals(2, my_global);
 
 eval("let foo = 1; function lazy() { foo = 2; } lazy(); my_global = foo;");
 assertEquals(my_global, 2);
+
+// Lexical variable inside a subscope in eval.
+eval(`{ let foo = 5;
+        function not_lazy() { foo = 6; }
+        not_lazy();
+        my_global = foo;
+      }`);
+assertEquals(my_global, 6);