Assert equal numbers of Start/End internal control flow labels

If the number of Start internal control flow labels does not equal the
number of End internal control flow labels, the result might be subtle
intermittent problems related to register allocation.

This change adds an assertion that, at the completion of the Register
Allocation Phase, the register allocator must not indicate that it's
still nested within a region of internal control flow nor popped out of
too many regions of internal control flow.

Signed-off-by:  Henry Zongaro <[email protected]>

Author: hzongaro

compiler/codegen/OMRCodeGenPhase.cpp

@@ -391,6 +391,8 @@ OMR::CodeGenPhase::performRegisterAssigningPhase(TR::CodeGenerator * cg, TR::Cod
       cg->jettisonAllSpills(); // Spill temps used before now may lead to conflicts if also used by register assignment
       cg->doRegisterAssignment(kindsToAssign);
 
+      TR_ASSERT_FATAL(cg->internalControlFlowNestingDepth() == 0, "The numbers of labels marked as Start or End of internal control flow were unequal:  internalControlFlowNestingDepth == %d\n", cg->internalControlFlowNestingDepth());
+
       if (comp->compilationShouldBeInterrupted(AFTER_REGISTER_ASSIGNMENT_CONTEXT))
          {
          comp->failCompilation<TR::CompilationInterrupted>("interrupted after RA");