[Mosaic] Support left shifting relayouts

PiperOrigin-RevId: 618008857

Author: tlongeri

jaxlib/mosaic/dialect/tpu/transforms/apply_vector_layout.cc

@@ -4349,38 +4349,56 @@ FailureOr<TypedValue<VectorType>> relayout(
         return emitError(v.getLoc(),
                          "Not implemented: Both columns and rows are shifted");
       }
-      if (col_diff < 0) {
-        return emitError(v.getLoc(), "Not implemented: Shifts to the left");
-      }
       if (bitwidth != 32 || tiling != target_shape) {
         return emitError(v.getLoc(),
                          "Not implemented: Only 32-bit column shifts for "
                          "native layouts supported");
       }
-      const int64_t sublane_diff = col_diff;
       TPU_ASSERT_GE_LOC(v.getLoc(), src_tiles.num_dimensions(), 1);
       std::optional<tpu::CreateMaskOp> maybe_create_mask;
-      if (src_tiles.dimensions()[src_tiles.num_dimensions() - 1] > 1) {
+      if (*(src_tiles.dimensions().end() - 1) > 1) {
+        int64_t lane_start, lane_end;
+        if (col_diff > 0) {
+          lane_start = 0;
+          lane_end = col_diff;
+        } else {  // col_diff < 0
+          lane_start = target_shape[1] + col_diff;
+          lane_end = target_shape[1];
+        }
         auto boundIdxConst =
             std::bind(IdxConst, std::placeholders::_1, builder, v.getLoc());
         maybe_create_mask = builder.create<tpu::CreateMaskOp>(
             v.getLoc(), VectorType::get(target_shape, builder.getI1Type()),
-            ValueRange{boundIdxConst(0), boundIdxConst(0)},
+            ValueRange{boundIdxConst(0), boundIdxConst(lane_start)},
             ValueRange{boundIdxConst(target_shape[0]),
-                       boundIdxConst(col_diff)});
+                       boundIdxConst(lane_end)});
       }
-      src_tiles.Each([&](absl::Span<const int64_t> idx, Value tile) {
-        Value rot_tile =
-            builder
-                .create<tpu::RotateOp>(v.getLoc(), tile,
-                                       /*amount=*/sublane_diff,
-                                       /*dimension=*/1, /*stride=*/nullptr,
-                                       /*stride_dimension=*/nullptr)
-                .getResult();
-        if (idx[idx.size() - 1] != 0) {
-          SmallVector<int64_t> prev_idx(idx.begin(), idx.end());
-          --prev_idx[idx.size() - 1];
-          Value prev_rot_tile = dst_tiles(prev_idx);
+      src_tiles.Each([&](absl::Span<const int64_t> idx, Value *tile) {
+        *tile = builder
+                    .create<tpu::RotateOp>(v.getLoc(), *tile,
+                                           /*amount=*/col_diff < 0
+                                               ? target_shape[1] + col_diff
+                                               : col_diff,
+                                           /*dimension=*/1, /*stride=*/nullptr,
+                                           /*stride_dimension=*/nullptr)
+                    .getResult();
+      });
+      src_tiles.Each([&](absl::Span<const int64_t> idx, Value rot_tile) {
+        Value prev_rot_tile;
+        if (col_diff > 0) {
+          if (*(idx.end() - 1) != 0) {
+            SmallVector<int64_t> prev_idx(idx.begin(), idx.end());
+            --*(prev_idx.end() - 1);
+            prev_rot_tile = src_tiles(prev_idx);
+          }
+        } else {  // col_diff < 0
+          if (*(idx.end() - 1) != *(src_tiles.dimensions().end() - 1) - 1) {
+            SmallVector<int64_t> prev_idx(idx.begin(), idx.end());
+            ++*(prev_idx.end() - 1);
+            prev_rot_tile = src_tiles(prev_idx);
+          }
+        }
+        if (prev_rot_tile != nullptr) {
           rot_tile = builder.create<arith::SelectOp>(
               v.getLoc(), maybe_create_mask->getResult(), prev_rot_tile,
               rot_tile);