Add simt functions in operators

docs/lang/articles/basic/operator.md

@@ -323,3 +323,52 @@ a@a             # @ denotes matrix multiplication
 For now, determinant() and inverse() only works in Taichi-scope, and the
 size of the matrix must be 1x1, 2x2, 3x3 or 4x4.
 :::
+
+
+## Supported SIMT intrinsics
+For CUDA backend, Taichi now supports warp-level and block-level intrinsics that
+are needed for writing high-performance SIMT kernels. You can use them in Taichi
+similar to the [usage in CUDA kernels](https://developer.nvidia.com/blog/using-cuda-warp-level-primitives/). Currently, the following functions are supported:
+
+
+| Operation                  | Mapped CUDA intrinsic         |
+| -------------------------- | ----------------------------- |
+|`ti.simt.warp.all_nonzero`  | `__all_sync`      |
+|`ti.simt.warp.any_nonzero`  | `__any_sync`      |
+|`ti.simt.warp.unique`       | `__uni_sync`      |
+|`ti.simt.warp.ballot`       | `__ballot_sync`   |
+|`ti.simt.warp.shfl_sync_i32`| `__shfl_sync`     |
+|`ti.simt.warp.shfl_sync_f32`| `__shfl_sync`     |
+|`ti.simt.warp.shfl_up_i32`  | `__shfl_up_sync`  |
+|`ti.simt.warp.shfl_up_f32`  | `__shfl_up_sync`  |
+|`ti.simt.warp.shfl_down_i32`| `__shfl_down_sync`|
+|`ti.simt.warp.shfl_down_f32`| `__shfl_down_sync`|
+|`ti.simt.warp.shfl_xor_i32` | `__shfl_xor_sync` |
+|`ti.simt.warp.match_any`    | `__match_any_sync`|
+|`ti.simt.warp.match_all`    | `__match_all_sync`|
+|`ti.simt.warp.active_mask`  | `__activemask`    |
+|`ti.simt.warp.sync`         | `__syncwarp`      |
+
+Please refer to our [API docs](https://docs.taichi.graphics/api/taichi/lang/simt/warp/#module-taichi.lang.simt.warp)
+for more information on each function.
+
+Here is an example to perform data exchange within a warp in Taichi:
+
+
+```python
+a = ti.field(dtype=ti.i32, shape=32)
+
+@ti.kernel
+def foo():
+    ti.loop_config(block_dim=32)
+    for i in range(32):
+        a[i] = ti.simt.warp.shfl_up_i32(ti.u32(0xFFFFFFFF), a[i], 1)
+
+for i in range(32):
+    a[i] = i * i
+
+foo()
+
+for i in range(1, 32):
+    assert a[i] == (i - 1) * (i - 1)
+```