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diff --git a/js/src/wasm/WasmCodegenConstants.h b/js/src/wasm/WasmCodegenConstants.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:
+ *
+ * Copyright 2021 Mozilla Foundation
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef wasm_codegen_constants_h
+#define wasm_codegen_constants_h
+
+#include <stdint.h>
+
+namespace js {
+namespace wasm {
+
+static const unsigned MaxArgsForJitInlineCall = 8;
+static const unsigned MaxResultsForJitEntry = 1;
+static const unsigned MaxResultsForJitExit = 1;
+static const unsigned MaxResultsForJitInlineCall = MaxResultsForJitEntry;
+// The maximum number of results of a function call or block that may be
+// returned in registers.
+static const unsigned MaxRegisterResults = 1;
+
+// A magic value of the InstanceReg to indicate after a return to the entry
+// stub that an exception has been caught and that we should throw.
+
+static const unsigned FailInstanceReg = 0xbad;
+
+// The following thresholds were derived from a microbenchmark. If we begin to
+// ship this optimization for more platforms, we will need to extend this list.
+
+#if defined(JS_CODEGEN_X64) || defined(JS_CODEGEN_ARM64)
+static const uint32_t MaxInlineMemoryCopyLength = 64;
+static const uint32_t MaxInlineMemoryFillLength = 64;
+#elif defined(JS_CODEGEN_X86)
+static const uint32_t MaxInlineMemoryCopyLength = 32;
+static const uint32_t MaxInlineMemoryFillLength = 32;
+#else
+static const uint32_t MaxInlineMemoryCopyLength = 0;
+static const uint32_t MaxInlineMemoryFillLength = 0;
+#endif
+
+// The size we round all super type vectors to. All accesses below this length
+// can avoid bounds checks. The value of 8 was chosen after a bit of profiling
+// with the Dart Barista benchmark.
+//
+// Keep jit-tests/tests/wasm/gc/casting.js in sync with this constant.
+static const uint32_t MinSuperTypeVectorLength = 8;
+
+// An exported wasm function may have a 'jit entry' stub attached that can be
+// called using the JS JIT ABI. This relies on the pointer we store in the
+// `NativeJitInfoOrInterpretedScriptSlot` slot of JSFunction to have a
+// compatible representation with BaseScript/SelfHostedLazyScript so that
+// `masm.loadJitCodeRaw` works.
+//
+// We store jit entry pointers in an array (see wasm::JumpTable) and store the
+// pointer to a function's jit entry in the JSFunction slot. We rely on the
+// below offset of each entry in the jump table to be compatible with
+// BaseScript/SelfHostedLazyScript.
+static const uint32_t JumpTableJitEntryOffset = 0;
+
+}  // namespace wasm
+}  // namespace js
+
+#endif  // wasm_codegen_constants_h