8194740: UseSubwordForMaxVector causes performance regression

Reviewed-by: kvn, thartmann

src/hotspot/share/opto/loopTransform.cpp

@@ -861,7 +861,9 @@ bool IdealLoopTree::policy_unroll(PhaseIdealLoop *phase) {
 
   // Check for being too big
   if (body_size > (uint)_local_loop_unroll_limit) {
-    if ((UseSubwordForMaxVector || xors_in_loop >= 4) && body_size < (uint)LoopUnrollLimit * 4) return true;
+    if ((cl->is_subword_loop() || xors_in_loop >= 4) && body_size < (uint)LoopUnrollLimit * 4) {
+      return true;
+    }
     // Normal case: loop too big
     return false;
   }

src/hotspot/share/opto/loopnode.hpp

@@ -75,7 +75,8 @@ protected:
          HasRangeChecks=8192,
          IsMultiversioned=16384,
          StripMined=32768,
-         ProfileTripFailed=65536};
+         SubwordLoop=65536,
+         ProfileTripFailed=131072};
   char _unswitch_count;
   enum { _unswitch_max=3 };
   char _postloop_flags;
@@ -99,6 +100,7 @@ public:
   bool partial_peel_has_failed() const { return _loop_flags & PartialPeelFailed; }
   bool is_strip_mined() const { return _loop_flags & StripMined; }
   bool is_profile_trip_failed() const { return _loop_flags & ProfileTripFailed; }
+  bool is_subword_loop() const { return _loop_flags & SubwordLoop; }
 
   void mark_partial_peel_failed() { _loop_flags |= PartialPeelFailed; }
   void mark_has_reductions() { _loop_flags |= HasReductions; }
@@ -112,6 +114,7 @@ public:
   void mark_strip_mined() { _loop_flags |= StripMined; }
   void clear_strip_mined() { _loop_flags &= ~StripMined; }
   void mark_profile_trip_failed() { _loop_flags |= ProfileTripFailed; }
+  void mark_subword_loop() { _loop_flags |= SubwordLoop; }
 
   int unswitch_max() { return _unswitch_max; }
   int unswitch_count() { return _unswitch_count; }

src/hotspot/share/opto/superword.cpp

@@ -376,6 +376,7 @@ void SuperWord::unrolling_analysis(int &local_loop_unroll_factor) {
                 if (same_type) {
                   max_vector = cur_max_vector;
                   flag_small_bt = true;
+                  cl->mark_subword_loop();
                 }
               }
             }