diff options
| -rw-r--r-- | polly/lib/Transform/ScheduleOptimizer.cpp | 21 |
1 files changed, 19 insertions, 2 deletions
diff --git a/polly/lib/Transform/ScheduleOptimizer.cpp b/polly/lib/Transform/ScheduleOptimizer.cpp index 354d65ded9b..a4fe301156c 100644 --- a/polly/lib/Transform/ScheduleOptimizer.cpp +++ b/polly/lib/Transform/ScheduleOptimizer.cpp @@ -867,8 +867,25 @@ createExtensionNode(__isl_take isl_schedule_node *Node, /// /// The packing transformation can be described as a data-layout /// transformation that requires to introduce a new array, copy data -/// to the array, and change memory access locations of the compute kernel -/// to reference the array. +/// to the array, and change memory access locations to reference the array. +/// It can be used to ensure that elements of the new array are read in-stride +/// access, aligned to cache lines boundaries, and preloaded into certain cache +/// levels. +/// +/// As an example let us consider the packing of the array A that would help +/// to read its elements with in-stride access. An access to the array A +/// is represented by an access relation that has the form +/// S[i, j, k] -> A[i, k]. The scheduling function of the SCoP statement S has +/// the form S[i,j, k] -> [floor((j mod Nc) / Nr), floor((i mod Mc) / Mr), +/// k mod Kc, j mod Nr, i mod Mr]. +/// +/// To ensure that elements of the array A are read in-stride access, we add +/// a new array Packed_A[Mc/Mr][Kc][Mr] to the SCoP, using +/// Scop::createScopArrayInfo, change the access relation +/// S[i, j, k] -> A[i, k] to +/// S[i, j, k] -> Packed_A[floor((i mod Mc) / Mr), k mod Kc, i mod Mr], using +/// MemoryAccess::setNewAccessRelation, and copy the data to the array, using +/// the copy statement created by Scop::addScopStmt. /// /// @param Node The schedule node to be optimized. /// @param MapOldIndVar The relation, which maps original induction variables |
