[8u] Fix Shenandoah bindings in ADLC formssel

[Aleksey Shipilev]

Hi,

While reading the sh/jdk8 difference against upstream, I realized that formssel.cpp changes are 
stale. We need to drop ShenandoahReadBarrier mentions, since there so no such node at all.

InstructForm::captures_bottom_type does have ShenandoahCompareAndExchangeP/N in later JDKs, but no 
such nodes are available in 8u. So I just dropped the unnecessary test.

MatchNode::needs_ideal_memory_edge needs ShenandoahCompareAndSwapN/P nodes, like all other JDK 
versions do. Actually, later JDK revisions add *Weak* and *CompareAndExchange* variants, but for 8u 
only CompareAndSwap are needed.

8u patch:

diff -r 25688d338e24 src/share/vm/adlc/formssel.cpp
--- a/src/share/vm/adlc/formssel.cpp    Wed Feb 17 17:39:25 2021 +0100
+++ b/src/share/vm/adlc/formssel.cpp    Thu Feb 18 12:27:37 2021 +0100
@@ -765,12 +765,11 @@
          !strcmp(_matrule->_rChild->_opType,"LoadN")        ||
          !strcmp(_matrule->_rChild->_opType,"LoadNKlass")   ||
          !strcmp(_matrule->_rChild->_opType,"CreateEx")     ||  // type of exception
          !strcmp(_matrule->_rChild->_opType,"CheckCastPP")  ||
          !strcmp(_matrule->_rChild->_opType,"GetAndSetP")   ||
-        !strcmp(_matrule->_rChild->_opType,"GetAndSetN")   ||
-        !strcmp(_matrule->_rChild->_opType,"ShenandoahReadBarrier"))) return true;
+        !strcmp(_matrule->_rChild->_opType,"GetAndSetN")) )  return true;
    else if ( is_ideal_load() == Form::idealP )                return true;
    else if ( is_ideal_store() != Form::none  )                return true;

    if (needs_base_oop_edge(globals)) return true;

@@ -3473,15 +3472,15 @@
      "StoreVector", "LoadVector",
      "LoadRange", "LoadKlass", "LoadNKlass", "LoadL_unaligned", "LoadD_unaligned",
      "LoadPLocked",
      "StorePConditional", "StoreIConditional", "StoreLConditional",
      "CompareAndSwapI", "CompareAndSwapL", "CompareAndSwapP", "CompareAndSwapN",
+    "ShenandoahCompareAndSwapN", "ShenandoahCompareAndSwapP",
      "StoreCM",
      "ClearArray",
      "GetAndAddI", "GetAndSetI", "GetAndSetP",
      "GetAndAddL", "GetAndSetL", "GetAndSetN",
-    "ShenandoahReadBarrier",
    };
    int cnt = sizeof(needs_ideal_memory_list)/sizeof(char*);
    if( strcmp(_opType,"PrefetchRead")==0 ||
        strcmp(_opType,"PrefetchWrite")==0 ||
        strcmp(_opType,"PrefetchAllocation")==0 )


Testing: hotspot_gc_shenandoah {fastdebug,release}

-- 
Thanks,
-Aleksey