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diff --git a/js/src/wasm/WasmFeatures.h b/js/src/wasm/WasmFeatures.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 js_wasm_WasmFeatures_h
+#define js_wasm_WasmFeatures_h
+
+#include "js/WasmFeatures.h"
+#include "js/TypeDecls.h"
+
+namespace js {
+
+class JSStringBuilder;
+
+namespace wasm {
+
+// Return whether WebAssembly can in principle be compiled on this platform (ie
+// combination of hardware and OS), assuming at least one of the compilers that
+// supports the platform is not disabled by other settings.
+//
+// This predicate must be checked and must be true to call any of the top-level
+// wasm eval/compile methods.
+
+bool HasPlatformSupport();
+
+// Return whether WebAssembly is supported on this platform. This determines
+// whether the WebAssembly object is exposed to JS in this context / realm and
+//
+// It does *not* guarantee that a compiler is actually available; that has to be
+// checked separately, as it is sometimes run-time variant, depending on whether
+// a debugger has been created or not.
+
+bool HasSupport(JSContext* cx);
+
+// Predicates for compiler availability.
+//
+// These three predicates together select zero or one baseline compiler and zero
+// or one optimizing compiler, based on: what's compiled into the executable,
+// what's supported on the current platform, what's selected by options, and the
+// current run-time environment.  As it is possible for the computed values to
+// change (when a value changes in about:config or the debugger pane is shown or
+// hidden), it is inadvisable to cache these values in such a way that they
+// could become invalid.  Generally it is cheap always to recompute them.
+
+bool BaselineAvailable(JSContext* cx);
+bool IonAvailable(JSContext* cx);
+
+// Test all three.
+
+bool AnyCompilerAvailable(JSContext* cx);
+
+// Asm.JS is translated to wasm and then compiled using the wasm optimizing
+// compiler; test whether this compiler is available.
+
+bool WasmCompilerForAsmJSAvailable(JSContext* cx);
+
+// Predicates for white-box compiler disablement testing.
+//
+// These predicates determine whether the optimizing compilers were disabled by
+// features that are enabled at compile-time or run-time.  They do not consider
+// the hardware platform on whether other compilers are enabled.
+//
+// If `reason` is not null then it is populated with a string that describes
+// the specific features that disable the compiler.
+//
+// Returns false on OOM (which happens only when a reason is requested),
+// otherwise true, with the result in `*isDisabled` and optionally the reason in
+// `*reason`.
+
+bool BaselineDisabledByFeatures(JSContext* cx, bool* isDisabled,
+                                JSStringBuilder* reason = nullptr);
+bool IonDisabledByFeatures(JSContext* cx, bool* isDisabled,
+                           JSStringBuilder* reason = nullptr);
+
+// Predicates for feature availability.
+//
+// The following predicates check whether particular wasm features are enabled,
+// and for each, whether at least one compiler is (currently) available that
+// supports the feature.
+
+// Streaming compilation.
+bool StreamingCompilationAvailable(JSContext* cx);
+
+// Caching of optimized code.  Implies both streaming compilation and an
+// optimizing compiler tier.
+bool CodeCachingAvailable(JSContext* cx);
+
+// Shared memory and atomics.
+bool ThreadsAvailable(JSContext* cx);
+
+#define WASM_FEATURE(NAME, ...) bool NAME##Available(JSContext* cx);
+JS_FOR_WASM_FEATURES(WASM_FEATURE)
+#undef WASM_FEATURE
+
+// SIMD operations.
+bool SimdAvailable(JSContext* cx);
+
+// Privileged content that can access experimental builtin modules.
+bool IsSimdPrivilegedContext(JSContext* cx);
+
+#if defined(ENABLE_WASM_SIMD) && defined(DEBUG)
+// Report the result of a Simd simplification to the testing infrastructure.
+void ReportSimdAnalysis(const char* data);
+#endif
+
+// Returns true if WebAssembly as configured by compile-time flags and run-time
+// options can support try/catch, throw, rethrow, and branch_on_exn (evolving).
+bool ExceptionsAvailable(JSContext* cx);
+
+}  // namespace wasm
+}  // namespace js
+
+#endif  // js_wasm_WasmFeatures_h