[mlir][RFC] Refactor layout representation in MemRefType

The change is based on the proposal from the following discussion:
https://llvm.discourse.group/t/rfc-memreftype-affine-maps-list-vs-single-item/3968

* Introduce `MemRefLayoutAttr` interface to get `AffineMap` from an `Attribute`
  (`AffineMapAttr` implements this interface).
* Store layout as a single generic `MemRefLayoutAttr`.

This change removes the affine map composition feature and related API.
Actually, while the `MemRefType` itself supported it, almost none of the upstream
can work with more than 1 affine map in `MemRefType`.

The introduced `MemRefLayoutAttr` allows to re-implement this feature
in a more stable way - via separate attribute class.

Also the interface allows to use different layout representations rather than affine maps.
For example, the described "stride + offset" form, which is currently supported in ASM parser only,
can now be expressed as separate attribute.

Reviewed By: ftynse, bondhugula

Differential Revision: https://reviews.llvm.org/D111553

1 files changed, 1 insertions, 8 deletions

diff --git a/mlir/lib/Analysis/LoopAnalysis.cpp b/mlir/lib/Analysis/LoopAnalysis.cpp
index d40958e87777..478b212c3b52 100644
--- a/mlir/lib/Analysis/LoopAnalysis.cpp
+++ b/mlir/lib/Analysis/LoopAnalysis.cpp
@@ -219,15 +219,8 @@ static bool isContiguousAccess(Value iv, LoadOrStoreOp memoryOp,
   assert(memRefDim && "memRefDim == nullptr");
   auto memRefType = memoryOp.getMemRefType();
 
-  auto layoutMap = memRefType.getAffineMaps();
-  // TODO: remove dependence on Builder once we support non-identity layout map.
-  Builder b(memoryOp.getContext());
-  if (layoutMap.size() >= 2 ||
-      (layoutMap.size() == 1 &&
-       !(layoutMap[0] ==
-         b.getMultiDimIdentityMap(layoutMap[0].getNumDims())))) {
+  if (!memRefType.getLayout().isIdentity())
     return memoryOp.emitError("NYI: non-trivial layoutMap"), false;
-  }
 
   int uniqueVaryingIndexAlongIv = -1;
   auto accessMap = memoryOp.getAffineMap();