[mlir][memref-to-spirv]: Reverse Image Load Coordinates

mlir/lib/Conversion/MemRefToSPIRV/MemRefToSPIRV.cpp

@@ -699,6 +699,35 @@ LoadOpPattern::matchAndRewrite(memref::LoadOp loadOp, OpAdaptor adaptor,
   return success();
 }
 
+template <typename OpAdaptor>
+static FailureOr<SmallVector<Value>>
+extractLoadCoordsForComposite(memref::LoadOp loadOp, OpAdaptor adaptor,
+                              ConversionPatternRewriter &rewriter) {
+  // At present we only support linear "tiling" as specified in Vulkan, this
+  // means that texels are assumed to be laid out in memory in a row-major
+  // order. This allows us to support any memref layout that is a permutation of
+  // the dimensions. Future work will pass an optional image layout to the
+  // rewrite pattern so that we can support optimized target specific tilings.
+  SmallVector<Value> indices = adaptor.getIndices();
+  AffineMap map = loadOp.getMemRefType().getLayout().getAffineMap();
+  if (!map.isPermutation())
+    return rewriter.notifyMatchFailure(
+        loadOp,
+        "Cannot lower memrefs with memory layout which is not a permutation");
+
+  // The memrefs layout determines the dimension ordering so we need to follow
+  // the map to get the ordering of the dimensions/indices.
+  const unsigned dimCount = map.getNumDims();
+  SmallVector<Value, 3> coords(dimCount);
+  for (unsigned dim = 0; dim < dimCount; ++dim)
+    coords[map.getDimPosition(dim)] = indices[dim];
+
+  // We need to reverse the coordinates because the memref layout is slowest to
+  // fastest moving and the vector coordinates for the image op is fastest to
+  // slowest moving.
+  return llvm::to_vector(llvm::reverse(coords));
+}
+
 LogicalResult
 ImageLoadOpPattern::matchAndRewrite(memref::LoadOp loadOp, OpAdaptor adaptor,
                                     ConversionPatternRewriter &rewriter) const {
@@ -755,13 +784,17 @@ ImageLoadOpPattern::matchAndRewrite(memref::LoadOp loadOp, OpAdaptor adaptor,
 
   // Build a vector of coordinates or just a scalar index if we have a 1D image.
   Value coords;
-  if (memrefType.getRank() != 1) {
+  if (memrefType.getRank() == 1) {
+    coords = adaptor.getIndices()[0];
+  } else {
+    FailureOr<SmallVector<Value>> maybeCoords =
+        extractLoadCoordsForComposite(loadOp, adaptor, rewriter);
+    if (failed(maybeCoords))
+      return failure();
     auto coordVectorType = VectorType::get({loadOp.getMemRefType().getRank()},
                                            adaptor.getIndices().getType()[0]);
     coords = spirv::CompositeConstructOp::create(rewriter, loc, coordVectorType,
-                                                 adaptor.getIndices());
-  } else {
-    coords = adaptor.getIndices()[0];
+                                                 maybeCoords.value());
   }
 
   // Fetch the value out of the image.