Comment and reword assert in Recompilation for jProfiling

jProfiling should not use either sampling or counting to trip
recompilation. For this kind of method bodies, we have emitted
recompilation test to check method invocation count and loop
frequency against tuned threshold to trip recompilation.

Signed-off-by: Rahil Shah <rahil@ca.ibm.com>

runtime/compiler/control/J9Recompilation.cpp

@@ -207,6 +207,10 @@ J9::Recompilation::beforeOptimization()
    //
    if (self()->isProfilingCompilation()) // this asks the bodyInfo
       {
+      // JProfiling should not use either sampling or counting mechanism to trip recompilation.
+      // Even though _useSampling is set to true here, at the end of compilation we disable sampling
+      // causing us to rely only on the in-body recompilation test that relies on block frequency counter
+      // to trip recompilation making sure we have enough profiling data to use in recompilation.
       _useSampling = _compilation->getProfilingMode() != JitProfiling;
       self()->findOrCreateProfileInfo()->setProfilingCount     (DEFAULT_PROFILING_COUNT);
       self()->findOrCreateProfileInfo()->setProfilingFrequency (DEFAULT_PROFILING_FREQUENCY);

runtime/compiler/p/codegen/PPCRecompilation.cpp

@@ -1,5 +1,5 @@
 /*******************************************************************************
- * Copyright (c) 2000, 2017 IBM Corp. and others
+ * Copyright (c) 2000, 2018 IBM Corp. and others
  *
  * This program and the accompanying materials are made available under
  * the terms of the Eclipse Public License 2.0 which accompanies this
@@ -167,7 +167,7 @@ TR::Instruction *TR_PPCRecompilation::generatePrologue(TR::Instruction *cursor)
       else
          {
          // This only applies to JitProfiling, as JProfiling uses sampling
-         TR_ASSERT(_compilation->getProfilingMode() == JitProfiling, "JProfiling should use sampling to trigger recompilation");
+         TR_ASSERT(_compilation->getProfilingMode() == JitProfiling, "JProfiling should not use counting mechanism to trip recompilation");
 
          cursor = generateTrg1Src1ImmInstruction(cg(), TR::InstOpCode::cmpi4, firstNode, cr0, gr0,   0, cursor);
          // this is just padding for consistent code length

runtime/compiler/x/codegen/X86Recompilation.cpp

@@ -1,5 +1,5 @@
 /*******************************************************************************
- * Copyright (c) 2000, 2017 IBM Corp. and others
+ * Copyright (c) 2000, 2018 IBM Corp. and others
  *
  * This program and the accompanying materials are made available under
  * the terms of the Eclipse Public License 2.0 which accompanies this
@@ -182,7 +182,7 @@ TR::Instruction *TR_X86Recompilation::generatePrologue(TR::Instruction *cursor)
          else
             {
             // This only applies to JitProfiling, as JProfiling uses sampling
-            TR_ASSERT(_compilation->getProfilingMode() == JitProfiling, "JProfiling should use sampling to trigger recompilation");
+            TR_ASSERT(_compilation->getProfilingMode() == JitProfiling, "JProfiling should not use counting mechanism to trigger recompilation");
             cursor = new (trHeapMemory()) TR::X86MemImmInstruction(cursor, CMP4MemImms, mRef, 0, cg());
             }