Use 'critical' reduction method when 'atomic' is not available but requested.

[omalyshe]

Summary

In case atomic reduction method is not available (the compiler can't generate it) the assertion failure occurred if KMP_FORCE_REDUCTION=atomic was specified.
This change replaces the assertion with a warning and sets the reduction method to the default one - 'critical'.

[jlpeyton]

LGTM.

runtime/src/i18n/en_US.txt

 # --------------------------------------------------------------------------------------------------
 
 # Meta information about message catalog.
 
 Language "English"
 Country  "USA"
 LangId   "1033"
 Version  "2"
-Revision "20160405"
+Revision "20160714"
 
 
 
 # --------------------------------------------------------------------------------------------------
 -*- STRINGS -*-
 # --------------------------------------------------------------------------------------------------
 
 # Strings are not complete messages, just fragments. We need to work on it and reduce number of

 AffGranGroupType             "%1$s: granularity=group is not supported with KMP_AFFINITY=%2$s. Using \"granularity=core\"."
 AffHWSubsetManySockets       "KMP_HW_SUBSET ignored: too many sockets requested."
 AffHWSubsetDeprecated        "KMP_HW_SUBSET \"o\" offset designator deprecated, please use @ prefix for offset value."
 AffUsingHwloc                "%1$s: Affinity capable, using hwloc."
 AffIgnoringHwloc             "%1$s: Ignoring hwloc mechanism."
 AffHwlocErrorOccurred        "%1$s: Hwloc failed in %2$s. Relying on internal affinity mechanisms."
 EnvSerialWarn                "%1$s must be set prior to OpenMP runtime library initialization; ignored."
 EnvVarDeprecated             "%1$s variable deprecated, please use %2$s instead."
+RedMethodNotSupported        "KMP_FORCE_REDUCTION: %1$s method is not supported; using critical."
 
 
 # --------------------------------------------------------------------------------------------------
 -*- HINTS -*-
 # --------------------------------------------------------------------------------------------------
 
 # Hints. Hint may be printed after a message. Usually it is longer explanation text or suggestion.
 # To maintain hint numbers (they are visible to customers), add new hints to the end.

runtime/src/kmp_runtime.c

#endif
     }
 
     // KMP_FORCE_REDUCTION
 
     // If the team is serialized (team_size == 1), ignore the forced reduction
     // method and stay with the unsynchronized method (empty_reduce_block)
     if( __kmp_force_reduction_method != reduction_method_not_defined && team_size != 1) {
 
-        PACKED_REDUCTION_METHOD_T forced_retval;
+        PACKED_REDUCTION_METHOD_T forced_retval = critical_reduce_block;
 
         int atomic_available, tree_available;
 
         switch( ( forced_retval = __kmp_force_reduction_method ) )
         {
-            case critical_reduce_block:
                 KMP_ASSERT( lck );              // lck should be != 0
                 break;
 
             case atomic_reduce_block:
                 atomic_available = FAST_REDUCTION_ATOMIC_METHOD_GENERATED;
-                KMP_ASSERT( atomic_available ); // atomic_available should be != 0
+                if( ! atomic_available ) {
+                    KMP_WARNING(RedMethodNotSupported, "atomic");
+                    forced_retval = critical_reduce_block;
+                }
                 break;
 
             case tree_reduce_block:
                 tree_available = FAST_REDUCTION_TREE_METHOD_GENERATED;
-                KMP_ASSERT( tree_available );   // tree_available should be != 0
+                if( ! tree_available ) {
+                    KMP_WARNING(RedMethodNotSupported, "tree");
+                    forced_retval = critical_reduce_block;
+                } else {
                     #if KMP_FAST_REDUCTION_BARRIER
                     forced_retval = TREE_REDUCE_BLOCK_WITH_REDUCTION_BARRIER;
                     #endif
+                }
                 break;
 
             default:
                 KMP_ASSERT( 0 ); // "unsupported method specified"
         }
 
         retval = forced_retval;
     }