Bug 1646378: Refactor CallFlags constructors r=jandem

In a later patch it will be useful to be able to declare a CallFlags and give it a value later.

Differential Revision: https://phabricator.services.mozilla.com/D81798

js/src/jit/CacheIR.h

@@ -269,6 +269,7 @@ class StubField {
 class CallFlags {
  public:
   enum ArgFormat : uint8_t {
+    Unknown,
     Standard,
     Spread,
     FunCall,
@@ -277,12 +278,12 @@ class CallFlags {
     LastArgFormat = FunApplyArray
   };
 
+  CallFlags() = default;
+  explicit CallFlags(ArgFormat format) : argFormat_(format) {}
   CallFlags(bool isConstructing, bool isSpread, bool isSameRealm = false)
       : argFormat_(isSpread ? Spread : Standard),
         isConstructing_(isConstructing),
         isSameRealm_(isSameRealm) {}
-  explicit CallFlags(ArgFormat format)
-      : argFormat_(format), isConstructing_(false), isSameRealm_(false) {}
 
   ArgFormat getArgFormat() const { return argFormat_; }
   bool isConstructing() const {
@@ -294,6 +295,7 @@ class CallFlags {
 
   uint8_t toByte() const {
     // See CacheIRReader::callFlags()
+    MOZ_ASSERT(argFormat_ != ArgFormat::Unknown);
     uint8_t value = getArgFormat();
     if (isConstructing()) {
       value |= CallFlags::IsConstructing;
@@ -305,9 +307,9 @@ class CallFlags {
   }
 
  private:
-  ArgFormat argFormat_;
-  bool isConstructing_;
-  bool isSameRealm_;
+  ArgFormat argFormat_ = ArgFormat::Unknown;
+  bool isConstructing_ = false;
+  bool isSameRealm_ = false;
 
   // Used for encoding/decoding
   static const uint8_t ArgFormatBits = 4;
@@ -385,6 +387,7 @@ inline int32_t GetIndexOfArgument(ArgumentKind kind, CallFlags flags,
       MOZ_ASSERT(kind <= ArgumentKind::Arg0);
       *addArgc = false;
       break;
+    case CallFlags::Unknown:
     case CallFlags::FunCall:
     case CallFlags::FunApplyArgs:
     case CallFlags::FunApplyArray:
@@ -977,6 +980,8 @@ class MOZ_RAII CacheIRReader {
     bool isConstructing = encoded & CallFlags::IsConstructing;
     bool isSameRealm = encoded & CallFlags::IsSameRealm;
     switch (format) {
+      case CallFlags::Unknown:
+        MOZ_CRASH("Unexpected call flags");
       case CallFlags::Standard:
         return CallFlags(isConstructing, /*isSpread =*/false, isSameRealm);
       case CallFlags::Spread: