diff --git a/js/src/jit/VMFunctions.h b/js/src/jit/VMFunctions.h
index 832014db6c94..5bb3505f5b2b 100644
--- a/js/src/jit/VMFunctions.h
+++ b/js/src/jit/VMFunctions.h
@@ -27,7 +27,7 @@ class TypedArrayObject;
 
 namespace jit {
 
-enum DataType {
+enum DataType : uint8_t {
     Type_Void,
     Type_Bool,
     Type_Int32,
@@ -40,14 +40,14 @@ enum DataType {
 
 struct PopValues
 {
-    uint32_t numValues;
+    uint8_t numValues;
 
-    explicit PopValues(uint32_t numValues)
+    explicit constexpr PopValues(uint8_t numValues)
       : numValues(numValues)
     { }
 };
 
-enum MaybeTailCall {
+enum MaybeTailCall : bool {
     TailCall,
     NonTailCall
 };
@@ -72,11 +72,24 @@ struct VMFunction
     // Address of the C function.
     void* wrapped;
 
+#ifdef JS_TRACE_LOGGING
     const char* name_;
+#endif
 
-    // Number of arguments expected, excluding JSContext * as an implicit
-    // first argument and an outparam as a possible implicit final argument.
-    uint32_t explicitArgs;
+    // Note: a maximum of seven root types is supported.
+    enum RootType : uint8_t {
+        RootNone = 0,
+        RootObject,
+        RootString,
+        RootId,
+        RootFunction,
+        RootValue,
+        RootCell
+    };
+
+    // Contains an combination of enumerated types used by the gc for marking
+    // arguments of the VM wrapper.
+    uint64_t argumentRootTypes;
 
     enum ArgProperties {
         WordByValue = 0,
@@ -96,6 +109,13 @@ struct VMFunction
     // have them.
     uint32_t argumentPassedInFloatRegs;
 
+    // Number of arguments expected, excluding JSContext * as an implicit
+    // first argument and an outparam as a possible implicit final argument.
+    uint8_t explicitArgs;
+
+    // The root type of the out param if outParam == Type_Handle.
+    RootType outParamRootType;
+
     // The outparam may be any Type_*, and must be the final argument to the
     // function, if not Void. outParam != Void implies that the return type
     // has a boolean failure mode.
@@ -110,28 +130,10 @@ struct VMFunction
     // nullptr before discarding its value.
     DataType returnType;
 
-    // Note: a maximum of seven root types is supported.
-    enum RootType {
-        RootNone = 0,
-        RootObject,
-        RootString,
-        RootId,
-        RootFunction,
-        RootValue,
-        RootCell
-    };
-
-    // Contains an combination of enumerated types used by the gc for marking
-    // arguments of the VM wrapper.
-    uint64_t argumentRootTypes;
-
-    // The root type of the out param if outParam == Type_Handle.
-    RootType outParamRootType;
-
     // Number of Values the VM wrapper should pop from the stack when it returns.
     // Used by baseline IC stubs so that they can use tail calls to call the VM
     // wrapper.
-    uint32_t extraValuesToPop;
+    uint8_t extraValuesToPop;
 
     // On some architectures, called functions need to explicitly push their
     // return address, for a tail call, there is nothing to push, so tail-callness
@@ -159,9 +161,11 @@ struct VMFunction
         return ((argumentPassedInFloatRegs >> explicitArg) & 1) == 1;
     }
 
+#ifdef JS_TRACE_LOGGING
     const char* name() const {
         return name_;
     }
+#endif
 
     // Return the stack size consumed by explicit arguments.
     size_t explicitStackSlots() const {
@@ -233,17 +237,19 @@ struct VMFunction
     VMFunction(void* wrapped, const char* name, uint32_t explicitArgs, uint32_t argumentProperties,
                uint32_t argumentPassedInFloatRegs, uint64_t argRootTypes,
                DataType outParam, RootType outParamRootType, DataType returnType,
-               uint32_t extraValuesToPop = 0, MaybeTailCall expectTailCall = NonTailCall)
+               uint8_t extraValuesToPop = 0, MaybeTailCall expectTailCall = NonTailCall)
       : next(nullptr),
         wrapped(wrapped),
+#ifdef JS_TRACE_LOGGING
         name_(name),
-        explicitArgs(explicitArgs),
+#endif
+        argumentRootTypes(argRootTypes),
         argumentProperties(argumentProperties),
         argumentPassedInFloatRegs(argumentPassedInFloatRegs),
+        explicitArgs(explicitArgs),
+        outParamRootType(outParamRootType),
         outParam(outParam),
         returnType(returnType),
-        argumentRootTypes(argRootTypes),
-        outParamRootType(outParamRootType),
         extraValuesToPop(extraValuesToPop),
         expectTailCall(expectTailCall)
     { }
@@ -251,14 +257,16 @@ struct VMFunction
     VMFunction(const VMFunction& o)
       : next(nullptr),
         wrapped(o.wrapped),
+#ifdef JS_TRACE_LOGGING
         name_(o.name_),
-        explicitArgs(o.explicitArgs),
+#endif
+        argumentRootTypes(o.argumentRootTypes),
         argumentProperties(o.argumentProperties),
         argumentPassedInFloatRegs(o.argumentPassedInFloatRegs),
+        explicitArgs(o.explicitArgs),
+        outParamRootType(o.outParamRootType),
         outParam(o.outParam),
         returnType(o.returnType),
-        argumentRootTypes(o.argumentRootTypes),
-        outParamRootType(o.outParamRootType),
         extraValuesToPop(o.extraValuesToPop),
         expectTailCall(o.expectTailCall)
     {