[NFC] Clarify comments in BubbleUpExpand shapes pass. (#19837)

The comments were written in terms of "fusion", but this pass is not
fusing, it is moving reshapes. Make that clear from comments.

Signed-off-by: MaheshRavishankar <[email protected]>

compiler/src/iree/compiler/DispatchCreation/BubbleUpExpandShapes.cpp

@@ -129,24 +129,28 @@ void BubbleUpExpandShapesPass::runOnOperation() {
           return false;
         }
 
-        // Do not fuse by expand if consumer is dequant.
+        // Do not push down collapse shape across consumer if it is a bit-extend
+        // op. The bit-extend ops get cloned into producer dispatches, and the
+        // `collapse_shape` op going past dequant, prevents this clong.
         if (IREE::LinalgExt::isBitExtendOp(consumer)) {
           return false;
         }
 
-        // Do not fuse producer generic op if it has more than one user
-        // or any reduction iterators.
+        // If producer generic op is elementwise op, bubble up the expand shape
+        // past this operation.
         if (auto producerGenericOp = dyn_cast<linalg::GenericOp>(producer)) {
           return llvm::all_of(producerGenericOp.getIteratorTypesArray(),
                               linalg::isParallelIterator);
         }
 
-        // Do not fuse with any producer linalg named ops for now.
+        // Do not bubble up expand shapes across named ops for now.
         if (isa<linalg::LinalgOp>(producer)) {
           return false;
         }
 
-        // Do not fuse with consumer linalg named ops or reductions.
+        // Do not push expand shapes down across operations with reduction
+        // iterator types.
+        // TODO: This condition should be removed.
         if (auto consumerLinalgOp = dyn_cast<linalg::LinalgOp>(consumer)) {
           return isa<linalg::GenericOp>(consumerLinalgOp) &&
                  llvm::all_of(consumerLinalgOp.getIteratorTypesArray(),