[Mosaic][TPU] Omit short circuiting of relayout (we should always rel…

…ayout!) and implement product mismatch case for where we relayout from replicated to offset, and the number of vregs changes.

PiperOrigin-RevId: 696226548

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

@@ -4723,6 +4723,11 @@ FailureOr<xla::Array<Value>> disassemble(
   TPU_ASSERT_LOC(val.getLoc(), def_layout.has_value());
   TPU_ASSERT_LOC(val.getLoc(),
                  def_layout->generalizes(layout, vty.getShape(), target_shape));
+  auto layout_product =
+      xla::Product(layout.tileArrayShape(vty.getShape(), target_shape));
+  auto def_layout_product =
+      xla::Product(def_layout->tileArrayShape(vty.getShape(), target_shape));
+  TPU_ASSERT_LOC(val.getLoc(), layout_product == def_layout_product);
   // TODO(tlongeri): Maybe just add a parameter to tileArrayShape instead of
   // having `tileArrayShape` and `tileArrayImplicitShape`.
   SmallVector<int64_t> layout_shape =
@@ -6324,11 +6329,50 @@ FailureOr<TypedValue<VectorType>> relayout(RewriteContext &ctx,
   if (src.generalizes(dst, vty.getShape(), target_shape)) {
     // A value with a replicated offset might use fewer vregs than a value with
     // a non-zero offset.
-    if (xla::Product(src.tileArrayShape(vty.getShape(), target_shape)) !=
-        xla::Product(dst.tileArrayShape(vty.getShape(), target_shape))) {
-      return emitError(v.getLoc(),
-                       "Not implemented: source layout is more general, but "
-                       "vreg count changes");
+    auto src_product =
+        xla::Product(src.tileArrayShape(vty.getShape(), target_shape));
+    auto dst_product =
+        xla::Product(dst.tileArrayShape(vty.getShape(), target_shape));
+    if (src_product != dst_product) {
+      TPU_ASSERT_LOC(v.getLoc(), dst_product > src_product);
+      auto src_offsets = src.offsets();
+
+      TPU_ASSERT_LOC(v.getLoc(), src_offsets != dst.offsets());
+      TPU_ASSERT_LOC(v.getLoc(), src.bitwidth() == dst.bitwidth());
+
+      if (src.implicit_dim() != dst.implicit_dim()) {
+        return emitError(v.getLoc(),
+                         "Not implemented: Source layout is more general, but "
+                         "vreg count changes and implicit dims are mismatched");
+      }
+
+      if (src.tiling() != dst.tiling()) {
+        return emitError(v.getLoc(),
+                         "Not implemented: Source layout is more general, but "
+                         "vreg count changes and tiling are mismatched");
+      }
+
+      // This case is moving from a replicated to a non replicated layout.
+      // As such, we need to make a new destination shape that is the
+      // materialization of the src shape with replication.
+      FAILUREOR_ASSIGN_OR_RETURN(auto src_vregs,
+                                 disassemble(builder, src, v, target_shape,
+                                             /*use_implicit_shape=*/true));
+      auto dst_vregs_shape = dst.tileArrayShape(vty.getShape(), target_shape);
+      xla::Array<Value> dst_vregs(dst_vregs_shape);
+      dst_vregs.Each([&](const absl::Span<const int64_t> idx, Value *vreg) {
+        SmallVector<int64_t> local_idx(idx.begin(), idx.end());
+        if (!src_offsets[0].has_value()) {
+          local_idx[local_idx.size() - 2] = 0;
+        }
+        if (!src_offsets[1].has_value()) {
+          local_idx[local_idx.size() - 1] = 0;
+        }
+        *vreg = src_vregs(local_idx);
+      });
+      return assemble(builder, vty, dst, std::move(dst_vregs), target_shape,
+                      /*use_implicit_shape=*/true)
+          .getResult();
     }
     src_tiles.Reshape(dst.tileArrayImplicitShape(vty.getShape(), target_shape));
     return assemble(builder, vty, dst, std::move(src_tiles), target_shape,
@@ -6411,8 +6455,6 @@ LogicalResult applyLayoutOp(RewriteContext &ctx, Operation &op) {
       if (vector_operand == nullptr) {
         continue;
       }
-      auto vty = vector_operand.getType();
-
       // The operand should always be an Operation (and not a BlockArgument)
       // since we expect the FuncOp to have only memrefs and semaphores as
       // arguments.
@@ -6427,9 +6469,6 @@ LogicalResult applyLayoutOp(RewriteContext &ctx, Operation &op) {
                                  getOutLayouts(*def_op, ctx.target_shape));
       const Layout lo = def_layouts[res_idx];
       TPU_ASSERT_OP(lo.has_value());
-      if (lo->generalizes(*li, vty.getShape(), ctx.target_shape)) {
-        continue;
-      }
       OpBuilder builder(&op);
       FAILUREOR_ASSIGN_OR_RETURN(
           Value new_v, relayout(ctx, builder, vector_operand, /*src=*/*lo,