[mlir][bufferization] Remove allow-return-allocs and create-deallocs pass options, remove bufferization.escape attribute

This is the first commit in a series with the goal to rework the
BufferDeallocation pass. Currently, this pass heavily relies on copies
to perform correct deallocations, which leads to very slow code and
potentially high memory usage. Additionally, there are unsupported cases
such as returning memrefs which this series of commits aims to add
support for as well.

This first commit removes the deallocation capabilities of
one-shot-bufferization.One-shot-bufferization should never deallocate any
memrefs as this should be entirely handled by the buffer-deallocation pass
going forward. This means the allow-return-allocs pass option will
default to true now, create-deallocs defaults to false and they, as well
as the escape attribute indicating whether a memref escapes the current region,
will be removed.

The documentation should w.r.t. these pass option changes should also be
updated in this commit.

Reviewed By: springerm

Differential Revision: https://reviews.llvm.org/D156662

mlir/lib/Dialect/SparseTensor/Transforms/SparseTensorConversion.cpp

@@ -962,7 +962,6 @@ public:
       const Type iTp = rewriter.getIndexType();
       Value dimCoords = genAlloca(rewriter, loc, dimRank, iTp);
       Value elemPtr = genAllocaScalar(rewriter, loc, elemTp);
-      Block *insertionBlock = rewriter.getInsertionBlock();
       // TODO: Dense buffers should be allocated/deallocated via the callback
       // in BufferizationOptions.
       Value dst = allocDenseTensor(rewriter, loc, dstTp, dimSizes);
@@ -982,11 +981,6 @@ public:
       genDelIteratorCall(rewriter, loc, elemTp, iter);
       rewriter.replaceOpWithNewOp<bufferization::ToTensorOp>(
           op, dstTp.getRankedTensorType(), dst);
-      // Deallocate the buffer.
-      if (bufferization::allocationDoesNotEscape(op->getOpResult(0))) {
-        rewriter.setInsertionPoint(insertionBlock->getTerminator());
-        deallocDenseTensor(rewriter, loc, dst);
-      }
       return success();
     }
     assert(!srcTp.hasEncoding() && dstTp.hasEncoding());