[opt] Eliminate redundant BitExtractStmt for SNode access under non-p…

…acked mode (taichi-dev#6485)

Issue: taichi-dev#6219

### Brief Summary

This PR adds optimization similar to taichi-dev#6444 for non-packed mode so that
we can conduct fair comparisons regarding performance. After this PR,
the benchmark script in taichi-dev#6219 runs `0.007s` on my local machine no
matter `packed=True/False`.

The tests are fixed because they are invalid - the out-of-bound access
used to be hidden by the always inserted `BitExtractStmt` before this
PR.

taichi/transforms/scalar_pointer_lowerer.cpp

@@ -90,17 +90,23 @@ void ScalarPointerLowerer::run() {
           auto const_next = lowered_->push_back<ConstStmt>(TypedConstant(next));
           extracted = lowered_->push_back<BinaryOpStmt>(
               BinaryOpType::div, indices_[k_], const_next);
-          is_first_extraction[k] = false;
         } else {
           extracted = generate_mod_x_div_y(lowered_, indices_[k_], prev, next);
         }
       } else {
         const int end = start_bits[k];
         start_bits[k] -= snode->extractors[k].num_bits;
         const int begin = start_bits[k];
-        extracted =
-            lowered_->push_back<BitExtractStmt>(indices_[k_], begin, end);
+        if (is_first_extraction[k] && begin == 0) {
+          // Similar optimization as above. In this case the full user
+          // coordinate is extracted so we don't need a BitExtractStmt.
+          extracted = indices_[k_];
+        } else {
+          extracted =
+              lowered_->push_back<BitExtractStmt>(indices_[k_], begin, end);
+        }
       }
+      is_first_extraction[k] = false;
       lowered_indices.push_back(extracted);
       strides.push_back(snode->extractors[k].shape);
     }

tests/python/test_sparse_activate.py

@@ -17,8 +17,8 @@ def test_pointer():
 
     @ti.kernel
     def activate():
-        ti.activate(ptr, 1)
-        ti.activate(ptr, 32)
+        ti.activate(ptr, ti.rescale_index(x, ptr, [1]))
+        ti.activate(ptr, ti.rescale_index(x, ptr, [32]))
 
     @ti.kernel
     def func():

tests/python/test_sparse_basics.py

@@ -34,13 +34,14 @@ def test_pointer_is_active():
 
     n = 128
 
-    ti.root.pointer(ti.i, n).dense(ti.i, n).place(x)
+    ptr = ti.root.pointer(ti.i, n)
+    ptr.dense(ti.i, n).place(x)
     ti.root.place(s)
 
     @ti.kernel
     def func():
         for i in range(n * n):
-            s[None] += ti.is_active(x.parent().parent(), i)
+            s[None] += ti.is_active(ptr, ti.rescale_index(x, ptr, [i]))
 
     x[0] = 1
     x[127] = 1

tests/python/test_sparse_parallel.py

@@ -58,7 +58,8 @@ def test_nested_struct_fill_and_clear():
     a = ti.field(dtype=ti.f32)
     N = 512
 
-    ti.root.pointer(ti.ij, [N, N]).dense(ti.ij, [8, 8]).place(a)
+    ptr = ti.root.pointer(ti.ij, [N, N])
+    ptr.dense(ti.ij, [8, 8]).place(a)
 
     @ti.kernel
     def fill():
@@ -68,7 +69,7 @@ def fill():
     @ti.kernel
     def clear():
         for i, j in a.parent():
-            ti.deactivate(a.parent().parent(), [i, j])
+            ti.deactivate(ptr, ti.rescale_index(a, ptr, [i, j]))
 
     def task():
         fill()