[Dlight] Enhance Decode-GEMV Rules

This PR enhances Decode-GEMV rule with the following changes:
- Normalize the GEMV iter domain to S-R-C via transform-block-layout.
  This would help with further analysis and scheduling, in cases for
  example, when there was no spatial loop in the original reduction
  block.
- Get rid of the ad hoc iter type analysis, including the logic calling
  into a TVM packed func `tir.schedule.GetLoopIterType` using
  `tvm._ffi.get_global_func`.
- Split out the logic for two separate cases of scheduling, where the
  innermost dimension is spatial or reduction.
- Introduces `suggest_threads_per_block` to guess the threads to be
  allocated each threadblock. This helps avoid the previous case where
  dlight allocates 256 threads for a workload whose degree of parallelism
  is only 128.
- Misc improvements.

This rest of the changes are split out to separate PRs that are already
merged to main.
- [x] Pass the hints to arithmetic analyzer that shape variables should
be positive ones (apache#15210)
- [x] Eliminate unnecessary block predicate generation - should be
provable via affine analysis (apache#15193)
- [x] Shrink local memory allocation if only one element `X[threadIdx.x]`
is used (apache#15207)

pyproject.toml

@@ -14,6 +14,10 @@
 # KIND, either express or implied.  See the License for the
 # specific language governing permissions and limitations
 # under the License.
+[tool.isort]
+profile = "black"
+src_paths = ["python", "tests/python"]
+
 
 [tool.black]
 line-length = 100

python/tvm/dlight/base/analysis.py

@@ -17,13 +17,12 @@
 """Analysis on TIR blocks, loops and functions."""
 from typing import List, Optional, Union
 
-from typing_extensions import Literal
-
 from tvm import tir
 from tvm._ffi import get_global_func
 from tvm.target.target import Target
 from tvm.tir import Schedule
 from tvm.tir.schedule import BlockRV
+from typing_extensions import Literal
 
 
 class IterInfo:

python/tvm/dlight/gpu/__init__.py

@@ -18,7 +18,7 @@
 GPU-generic schedule rules.
 For CUDA/ROCm/Vulkan/Metal-specific rules, use `tvm.dlight.cuda/rocm/vulkan/metal` instead
 """
-from .fallback import Fallback
 from .decode_gemv import DecodeGEMV
-from .reduction import Reduction
+from .fallback import Fallback
 from .matmul import Matmul
+from .reduction import Reduction

python/tvm/dlight/gpu/decode_gemv.py

@@ -14,19 +14,20 @@
 # KIND, either express or implied.  See the License for the
 # specific language governing permissions and limitations
 # under the License.
-# pylint: disable=missing-docstring
-"""A fallback schedule rule for GPU operators."""
-# pylint: disable=invalid-name
+"""A rule for DecodeGEMV."""
+from typing import List, Optional, Set, Tuple, Union
 
-from typing import List, Optional, Union
-
-from tvm import tir
-from tvm._ffi import get_global_func
-from tvm.arith import normalize_to_iter_sum
+from tvm import arith, tir
 from tvm.ir import structural_equal
 from tvm.target import Target
 
-from ..base import ScheduleRule, normalize_prim_func, try_inline_contiguous_spatial
+from ..base import (
+    BlockInfo,
+    ScheduleRule,
+    normalize_prim_func,
+    try_inline_contiguous_spatial,
+)
+from . import utils
 
 
 def _get_reduction_expr(block: tir.Block) -> Optional[tir.PrimExpr]:
@@ -47,13 +48,13 @@ def _get_reduction_expr(block: tir.Block) -> Optional[tir.PrimExpr]:
 
 def _detect_dominant_read(block: tir.Block) -> tir.PrimExpr:
     dominant_read, read_iters = None, None
-    tir_vars = set()
+    tir_vars: Set[tir.Var] = set()
     for buffer_region in block.reads:
         tir_vars.clear()
 
-        def _collect_tir_var(e):
-            if isinstance(e, tir.Var):
-                tir_vars.add(e)
+        def _collect_tir_var(expr):
+            if isinstance(expr, tir.Var):
+                tir_vars.add(expr)
 
         for expr in buffer_region.region:
             assert expr.extent == 1
@@ -68,27 +69,18 @@ def _collect_tir_var(e):
 
 
 class DecodeGEMV(ScheduleRule):
-    def __init__(self) -> None:
-        super().__init__()
-        self.get_loop_iter_type = get_global_func("tir.schedule.GetLoopIterType")
+    """A rule for DecodeGEMV."""
 
-    def apply(  # pylint: disable=too-many-locals
+    def apply(  # pylint: disable=too-many-locals,too-many-branches,too-many-return-statements
         self,
         func: tir.PrimFunc,
         target: Target,
         _: bool,
     ) -> Union[None, tir.Schedule, List[tir.Schedule]]:
         if not isinstance(func, tir.PrimFunc):
             return None
-
-        if target.kind.name == "cuda":
-            len_tx, len_ty = 16, 16
-        else:
-            len_tx, len_ty = 8, 8
-
         sch = tir.Schedule(func)
         block_infos = try_inline_contiguous_spatial(sch, normalize_prim_func(sch))
-
         if block_infos is None or len(block_infos) > 2:
             return None
 
@@ -97,96 +89,143 @@ def apply(  # pylint: disable=too-many-locals
         block_stmt = sch.get(block)
 
         # Step 1. Check reduction block
-        if not block_info.is_reduction():
+        if (
+            (not block_info.is_reduction())
+            or len(block_stmt.writes) != 1
+            or _get_reduction_expr(block_stmt) is None
+        ):
             return None
-        if len(block_stmt.writes) != 1:
-            return None
-        if _get_reduction_expr(block_stmt) is None:
-            return None
-
-        # Step 2. Sort out the spatial and reduction loops
-        sorted_iter_access = normalize_to_iter_sum(
-            _detect_dominant_read(block_stmt),
-            input_iters={i.var: i.dom for i in block_stmt.iter_vars},
+        # Step 2. Normalize the block, merge spatial and reduction iters
+        is_inner_reduction, c_factor = self._normalize(
+            sch,
+            block_info,
+            arith.normalize_to_iter_sum(
+                _detect_dominant_read(block_stmt),
+                input_iters={i.var: i.dom for i in block_stmt.iter_vars},
+            ),
         )
-        if sorted_iter_access.base != 0:
-            return None
-        iter_to_info = {i.var: i for i in block_info.iters}
-        s_loops, r_loops, c_loops = [], [], []
-        for split in sorted_iter_access.args:
-            block_var = split.source.source
-            block_var_info = iter_to_info[block_var]
-            loop_rv = block_var_info.loop_rv
-            is_inner_reduction = block_var_info.kind == "R"
-            if split.lower_factor > 1:
-                c_loop_factor = split.lower_factor
-                loop_rv, c_loop = sch.split(loop_rv, factors=[None, c_loop_factor])
-                c_loops.append(c_loop)
-                is_loop_c_reduction = is_inner_reduction
-            if is_inner_reduction:
-                r_loops.append(loop_rv)
-            else:
-                s_loops.append(loop_rv)
-
-        if len(c_loops) > 1:
-            return None
-        if len(s_loops) != len([_ for i in block_info.iters if i.kind == "S"]):
+        if is_inner_reduction is None and c_factor is None:
             return None
-        if len(s_loops) == 0 or len(r_loops) == 0:
-            return None
-
-        sch.reorder(*s_loops, *r_loops, *c_loops)
-        s = sch.fuse(*s_loops)
-        r = sch.fuse(*r_loops)
-
-        if is_inner_reduction:
-            _, tx = sch.split(r, factors=[None, len_tx * len_ty])
-            rf = sch.rfactor(tx, 0)
-            s, r, tx = sch.get_loops(rf)[:3]
-            sch.reorder(s, tx, r)
-            sch.reverse_compute_at(block, s, preserve_unit_loops=True)
-            sch.bind(tx, "threadIdx.x")
-            sch.bind(s, "blockIdx.x")
-        else:
-            sch.split(s, factors=[None, len_tx])
-            _, ty = sch.split(r, factors=[None, len_ty])
-            rf = sch.rfactor(ty, 0)
-            bx, tx, r, ty = sch.get_loops(rf)[:4]
-            sch.reorder(bx, tx, ty, r)
-            sch.reverse_compute_at(block, bx, preserve_unit_loops=True)
-            sch.bind(tx, "threadIdx.x")
-            sch.bind(ty, "threadIdx.y")
-            sch.bind(bx, "blockIdx.x")
-
-        s_loops, r_loops = [], []
-        for loop_rv in sch.get_loops(block)[1:]:
-            iter_type = self.get_loop_iter_type(sch, loop_rv)
-            if iter_type == "S":
-                s_loops.append(loop_rv)
-            elif iter_type == "R":
-                r_loops.append(loop_rv)
-            else:
-                raise RuntimeError("Unknown loop type " + str(iter_type))
-        sch.reorder(*s_loops, *r_loops)
-        s_ctr = sch.fuse(*s_loops)
-        r_ctr = sch.fuse(*r_loops)
-
-        if c_loops and not is_loop_c_reduction:
-            s_ctr, inner = sch.split(s_ctr, factors=[None, c_loop_factor])
-            sch.reorder(s_ctr, r_ctr, inner)
-
+        # Step 3. Do the scheduling
         if is_inner_reduction:
-            sch.bind(r_ctr, "threadIdx.x")
-            sch.set_scope(rf, 0, "local")
-            sch.decompose_reduction(rf, sch.get_loops(rf)[2])
+            self._sch_inner_reduction(sch, target, block, c_factor)
         else:
-            sch.bind(s_ctr, "threadIdx.x")
-            sch.bind(r_ctr, "threadIdx.y")
-            sch.set_scope(rf, 0, "local")
-            sch.decompose_reduction(rf, sch.get_loops(rf)[3])
-
+            self._sch_inner_spatial(sch, target, block, c_factor)
+        # Step 4. Schedule epilogue
         if len(block_infos) == 2:
             sch.set_scope(block, 0, "local")
             sch.reverse_compute_at(block_infos[1].block_rv, sch.get_loops(block)[0])
-
         return sch
+
+    def _normalize(
+        self,
+        sch: tir.Schedule,
+        block_info: BlockInfo,
+        iter_sum: arith.IterSumExpr,
+    ) -> Tuple[Optional[bool], Optional[int]]:
+        if iter_sum.base != 0:
+            return None, None
+        iter_to_info = {i.var: i for i in block_info.iters}
+        s_dom, r_dom, c_dom, c_factor = None, None, None, None
+        for split in iter_sum.args:
+            var = split.source.source
+            info = iter_to_info[var]
+            dom = info.dom
+            is_inner_reduction = info.kind == "R"
+            if split.lower_factor > 1:
+                if c_dom is not None:
+                    return None, None
+                c_dom = tir.floormod(var, split.lower_factor)
+                var = tir.floordiv(var, split.lower_factor)
+                dom = tir.floordiv(dom, split.lower_factor)
+                if not is_inner_reduction:
+                    c_factor = split.lower_factor
+            if is_inner_reduction:
+                if r_dom is None:
+                    r_dom = var
+                else:
+                    r_dom = r_dom * dom + var
+            else:
+                if s_dom is None:
+                    s_dom = var
+                else:
+                    s_dom = s_dom * dom + var
+
+        assert r_dom is not None
+        if s_dom is None:
+            s_dom = tir.const(1, r_dom.dtype)
+        if c_dom is None:
+            c_dom = tir.const(1, r_dom.dtype)
+        sch.transform_block_layout(
+            block_info.block_rv,
+            tir.IndexMap(
+                [i.var for i in block_info.iters],
+                [s_dom, r_dom, c_dom],
+                None,
+            ),
+        )
+        return is_inner_reduction, c_factor
+
+    def _sch_inner_reduction(
+        self,
+        sch: tir.Schedule,
+        target: Target,
+        block: tir.schedule.BlockRV,
+        unroll_spatial_factor: Optional[int],
+    ):
+        # pylint: disable=invalid-name
+        _, r, _ = sch.get_loops(block)
+        (len_tx,) = utils.suggest_threads_per_block(  # pylint: disable=unbalanced-tuple-unpacking
+            target, [sch.get(r)]
+        )
+
+        _, tx = sch.split(r, factors=[None, len_tx])
+        rf = sch.rfactor(tx, 0)
+        s, r, tx = sch.get_loops(rf)[:3]
+        sch.reorder(s, tx, r)
+        sch.reverse_compute_at(block, s, preserve_unit_loops=True)
+        sch.bind(tx, "threadIdx.x")
+        sch.bind(s, "blockIdx.x")
+
+        _, r, *s = sch.get_loops(block)
+        s = sch.fuse(*s)
+        sch.reorder(s, r)
+        if unroll_spatial_factor:
+            s, inner = sch.split(s, factors=[None, unroll_spatial_factor])
+            sch.reorder(s, r, inner)
+        sch.bind(r, "threadIdx.x")
+        sch.set_scope(rf, 0, "local")
+        sch.decompose_reduction(rf, sch.get_loops(rf)[2])
+        # pylint: enable=invalid-name
+
+    def _sch_inner_spatial(
+        self,
+        sch: tir.Schedule,
+        _: Target,
+        block: tir.schedule.BlockRV,
+        unroll_spatial_factor: Optional[int],
+    ):
+        # pylint: disable=invalid-name
+        s, r, _ = sch.get_loops(block)
+        len_tx, len_ty = 16, 16
+        sch.split(s, factors=[None, len_tx])
+        _, ty = sch.split(r, factors=[None, len_ty])
+        rf = sch.rfactor(ty, 0)
+        bx, tx, r, ty = sch.get_loops(rf)[:4]
+        sch.reorder(bx, tx, ty, r)
+        sch.reverse_compute_at(block, bx, preserve_unit_loops=True)
+        sch.bind(tx, "threadIdx.x")
+        sch.bind(ty, "threadIdx.y")
+        sch.bind(bx, "blockIdx.x")
+
+        _, r, *s = sch.get_loops(block)
+        s = sch.fuse(*s)
+        sch.reorder(s, r)
+        if unroll_spatial_factor:
+            s, inner = sch.split(s, factors=[None, unroll_spatial_factor])
+            sch.reorder(s, r, inner)
+        sch.bind(s, "threadIdx.x")
+        sch.bind(r, "threadIdx.y")
+        sch.set_scope(rf, 0, "local")
+        sch.decompose_reduction(rf, sch.get_loops(rf)[3])
+        # pylint: enable=invalid-name

python/tvm/dlight/gpu/fallback.py

@@ -21,7 +21,8 @@
 from tvm import tir
 from tvm.target import Target
 
-from ..base import ScheduleRule, analysis, normalize_prim_func, try_inline
+from ..base import ScheduleRule, normalize_prim_func, try_inline
+from . import utils
 
 
 class Fallback(ScheduleRule):
@@ -36,7 +37,7 @@ def apply(  # pylint: disable=too-many-locals,missing-docstring
         target: Target,
         _: bool,
     ) -> tir.Schedule:
-        max_threads_per_block = analysis.get_max_threads_per_block(target)
+        max_threads_per_block = utils.max_threads_per_block(target)
 
         sch = tir.Schedule(func)
         block_infos = try_inline(sch, normalize_prim_func(sch))

python/tvm/dlight/gpu/matmul.py

@@ -16,14 +16,14 @@
 # under the License.
 # pylint: disable=missing-docstring, invalid-name
 """A GEMM schedule rule for GPU operators."""
-from enum import Enum
 from dataclasses import dataclass
+from enum import Enum
 from typing import Dict, List, Optional, Set, Tuple
 
 from tvm import tir
 from tvm.ir import Range
 from tvm.target import Target
-from tvm.tir import PrimExpr, Var, IterVar
+from tvm.tir import IterVar, PrimExpr, Var
 from tvm.tir.analysis import undefined_vars
 from tvm.tir.schedule.schedule import BlockRV