1 files changed, 30 insertions, 0 deletions
diff --git a/js/src/frontend/ValueUsage.h b/js/src/frontend/ValueUsage.h
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+++ b/js/src/frontend/ValueUsage.h
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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * vim: set ts=8 sts=2 et sw=2 tw=80:
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef frontend_ValueUsage_h
+#define frontend_ValueUsage_h
+
+namespace js {
+namespace frontend {
+
+// Used to control whether the expression result is used. This enables various
+// optimizations, for example it allows to emit JSOp::CallIgnoresRv for function
+// calls.
+enum class ValueUsage {
+  // Assume the value of the current expression may be used. This is always
+  // correct but prohibits optimizations like JSOp::CallIgnoresRv.
+  WantValue,
+
+  // Pass this when emitting an expression if the expression's value is
+  // definitely unused by later instructions. You must make sure the next
+  // instruction is JSOp::Pop, a jump to a JSOp::Pop, or something similar.
+  IgnoreValue
+};
+
+} /* namespace frontend */
+} /* namespace js */
+
+#endif /* frontend_ValueUsage_h */