fixThreadsBelowFilter: always fix all remaining thread identifiers to zero

Since 497d3c4 (complete thread mapping in a single band,
Thu Apr 12 10:00:09 2018 +0200), a branch is mapped
to all thread identifiers as soon as it gets mapped to any thread identifier.
There is therefore no longer any need to specify the range
of thread identifiers to fix in fixThreadsBelowFilter
as it is always equal to the total number of thread identifiers.

Author: Sven Verdoolaege

tc/core/polyhedral/cuda/mapped_scop.cc

@@ -147,13 +147,13 @@ void MappedScop::mapToBlocksAndScaleBand(
 /*
  * Given a filter node in the schedule tree of a mapped scop,
  * insert another filter underneath (if needed) that fixes
- * the thread identifiers in the range [begin, end) to zero.
+ * the remaining thread identifiers starting at "begin" to zero.
  */
 void fixThreadsBelowFilter(
     MappedScop& mscop,
     detail::ScheduleTree* filterTree,
-    size_t begin,
-    size_t end) {
+    size_t begin) {
+  size_t end = mscop.numThreads.view.size();
   if (begin == end) {
     return;
   }
@@ -413,21 +413,16 @@ bool hasOuterSequentialMember(
 // If any separation is needed for mapping reductions to full blocks,
 // then do so first.
 //
-// If "st" has multiple children, then make sure they are mapped
-// to the same number of thread identifiers by fixing those
-// that are originally mapped to fewer identifiers to value zero
-// for the remaining thread identifiers.
+// If "st" has multiple children and if any of those children
+// is mapped to threads, then make sure the other children
+// are also mapped to threads, by fixing the thread identifiers to value zero.
 // If, moreover, "st" is a sequence node and at least one of its
 // children is mapped to threads, then introduce synchronization
 // before and after children that are mapped to threads.
 // Also add synchronization between the last child and
 // the next iteration of the first child if there may be such
 // a next iteration that is not already covered by synchronization
 // on an outer node.
-// If any synchronization is introduced, then the mapping
-// to threads needs to be completed to all thread ids
-// because the synchronization needs to be introduced outside
-// any mapping to threads.
 size_t MappedScop::mapInnermostBandsToThreads(detail::ScheduleTree* st) {
   if (needReductionSeparation(st)) {
     st = separateReduction(st);
@@ -441,11 +436,10 @@ size_t MappedScop::mapInnermostBandsToThreads(detail::ScheduleTree* st) {
   auto n = nChildren > 0 ? *std::max_element(nInner.begin(), nInner.end()) : 0;
   if (nChildren > 1) {
     auto needSync = st->elemAs<detail::ScheduleTreeElemSequence>() && n > 0;
-    if (needSync) {
-      n = numThreads.view.size();
-    }
-    for (size_t i = 0; i < nChildren; ++i) {
-      fixThreadsBelowFilter(*this, children[i], nInner[i], n);
+    if (n > 0) {
+      for (size_t i = 0; i < nChildren; ++i) {
+        fixThreadsBelowFilter(*this, children[i], nInner[i]);
+      }
     }
     if (needSync) {
       auto outer = hasOuterSequentialMember(scop_->scheduleRoot(), st);