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Update the documentation on how the packing transformation is implemented 

Add a simple example to update the documentation on how the packing
transformation is implemented.

Reviewed-by: Tobias Grosser <tobias@grosser.es>,
             Michael Kruse <llvm@meinersbur.de>

Differential Revision: https://reviews.llvm.org/D28021

llvm-svn: 293429
This commit is contained in:
Roman Gareev 2017-01-29 10:37:50 +00:00
parent 9f376b7b37
commit 7758a2af53
1 changed files with 19 additions and 2 deletions
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21
polly/lib/Transform/ScheduleOptimizer.cpp
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@ -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