fix(compiler): Use maps with symbolic offsets in memref casts for wrapper functions

The bufferization of the BConcrete dialect emits calls to Concrete
wrapper functions and casts all memrefs to ranked memrefs with dynamic
strides and an implicit identity layout map. The implicit identity map
does not allow for casts of memrefs with non-zero offsets, e.g.,
resulting from folding of memrefs related to intermediate results
passed as operands to the operation implemented by a wrapper.

Casting to memrefs symbolic offsets in the layout map (e.g.,
`[d0, d1, ...](s0, s1, ...) -> (d0 + s0, d1 + s1, ...)`) allows
for more flexibility, in particular this adds support for memrefs
with non-zero, constant offsets returned by operations generating
intermediate results.

compiler/lib/Dialect/BConcrete/Transforms/BufferizableOpInterfaceImpl.cpp

@@ -36,12 +36,31 @@ namespace {} // namespace
 
 namespace {
 
+// Returns a map with a symbolic offset for each dimension, i.e., for N
+// dimensions, it returns
+//
+// [d1, d2, ..., dN](s1, s2, ..., sN) -> (d1 + s1, d2 + s2, ..., dN + sN)
+//
+AffineMap getMultiDimSymbolicOffsetMap(mlir::RewriterBase &rewriter,
+                                       unsigned rank) {
+  SmallVector<AffineExpr, 4> dimExprs;
+  dimExprs.reserve(rank);
+
+  for (unsigned i = 0; i < rank; ++i)
+    dimExprs.push_back(rewriter.getAffineDimExpr(i) +
+                       rewriter.getAffineSymbolExpr(i));
+
+  return AffineMap::get(/*dimCount=*/rank, /*symbolCount=*/rank, dimExprs,
+                        rewriter.getContext());
+}
+
 mlir::Type getDynamicMemrefWithUnknownOffset(mlir::RewriterBase &rewriter,
                                              size_t rank) {
   mlir::MLIRContext *ctx = rewriter.getContext();
   std::vector<int64_t> shape(rank, -1);
+
   return mlir::MemRefType::get(shape, rewriter.getI64Type(),
-                               rewriter.getMultiDimIdentityMap(rank));
+                               getMultiDimSymbolicOffsetMap(rewriter, rank));
 }
 
 // Returns `memref.cast %0 : memref<...xAxT> to memref<...x?xT>`