[TensorIR][Pass][M1c] FlattenBuffer (apache#7962)

Co-authored-by: Tianqi Chen <tqchen@users.noreply.github.com>
Co-authored-by: Ruihang Lai <lairuihangdongdong@qq.com>

include/tvm/tir/transform.h

@@ -406,6 +406,14 @@ TVM_DLL Pass ConvertBlocksToOpaque();
  */
 TVM_DLL Pass CompactBufferAllocation();
 
+/*!
+ * \brief Flatten the multi-dimensional BufferLoad and BufferStore
+ *        to single dimensional Load/Store. Also remove Block to
+ *        ensure that the flattened TIR can not be scheduled again.
+ * \return The pass.
+ */
+TVM_DLL Pass FlattenBuffer();
+
 }  // namespace transform
 }  // namespace tir
 }  // namespace tvm

python/tvm/script/intrin.py

@@ -121,7 +121,7 @@ def floormod(x, y, span):
 
 
 @register
-def load(dtype, var, index, predicate=True, span=None):
+def load(dtype, var, index, predicate=None, span=None):
     return tvm.tir.Load(dtype, var, index, predicate, span)
 
 

python/tvm/script/scope_handler.py

@@ -154,15 +154,17 @@ class LaunchThread(WithScopeHandler):
     def __init__(self):
         def launch_thread(env_var, extent, span):
             extent = tvm.runtime.convert(extent, span=span)
+            thread_id = self.context.func_var_env_dict[env_var]
+            attr_key = "virtual_thread" if thread_id == "vthread" else "thread_extent"
             return tvm.tir.AttrStmt(
                 IterVar(
-                    None,
+                    (0, extent),
                     env_var,
                     getattr(IterVar, "ThreadIndex"),
-                    self.context.func_var_env_dict[env_var],
+                    thread_id,
                     span=span,
                 ),
-                "thread_extent",
+                attr_key,
                 extent,
                 self.body,
                 span=span,

python/tvm/tir/transform/transform.py

@@ -610,3 +610,16 @@ def CompactBufferAllocation():
         The result pass
     """
     return _ffi_api.CompactBufferAllocation()
+
+
+def FlattenBuffer():
+    """Flatten the multi-dimensional BufferLoad and BufferStore
+    to single dimensional Load/Store. Also remove Block to
+    ensure that the flattened TIR can not be scheduled again.
+
+    Returns
+    -------
+    fpass : tvm.transform.Pass
+        The result pass
+    """
+    return _ffi_api.FlattenBuffer()

src/printer/tvmscript_printer.cc

@@ -620,9 +620,9 @@ Doc TVMScriptPrinter::VisitStmt_(const AttrStmtNode* op) {
     }
   }
   // concise thread env
-  if (op->node->IsInstance<IterVarNode>() && op->attr_key == "thread_extent") {
+  if (op->node->IsInstance<IterVarNode>() &&
+      (op->attr_key == "thread_extent" || op->attr_key == "virtual_thread")) {
     const auto* iter_var = Downcast<IterVar>(op->node).get();
-    ICHECK(!iter_var->dom.defined());
     var_not_in_headers.insert(iter_var->var.get());
     var_env_map_[iter_var->var] = iter_var->thread_tag;
     if (current_num_ != num_child_ - 1) {

src/tir/transforms/flatten_buffer.cc

@@ -0,0 +1,172 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+/*!
+ * \file flatten_buffer.cc
+ */
+
+#include <tvm/tir/builtin.h>
+#include <tvm/tir/function.h>
+#include <tvm/tir/op.h>
+#include <tvm/tir/stmt_functor.h>
+#include <tvm/tir/transform.h>
+
+#include "../../support/utils.h"
+
+namespace tvm {
+namespace tir {
+
+PrimExpr BufferArea(const Buffer& buffer) {
+  PrimExpr area = Integer(1);
+  for (const PrimExpr& dim : buffer->shape) {
+    area = area * dim;
+  }
+  return area;
+}
+
+/*!
+ * \brief Transform multi-dimension BufferLoad/BufferStore into one-dimension Load/Store
+ */
+class BufferFlattener : public StmtExprMutator {
+ public:
+  static Stmt Flatten(const PrimFunc& f) { return BufferFlattener().VisitStmt(f->body); }
+
+ private:
+  Stmt VisitStmt_(const BlockRealizeNode* op) final {
+    // We have convert blocks into opaque blocks in previous passes.
+    ICHECK(op->iter_values.empty()) << "Non-opaque blocks are not allowed in FlattenBuffer. Please "
+                                       "call pass ConvertBlocksToOpaque before.";
+    // Step 1. Visit the body
+    Block new_block = Downcast<Block>(this->VisitStmt(op->block));
+    PrimExpr predicate = this->VisitExpr(op->predicate);
+    // Step 2. Transform the `predicate` to if-then-else
+    Stmt body = new_block->body;
+    if (!is_one(predicate)) {
+      body = IfThenElse(predicate, std::move(body));
+    }
+    // Step 3. Handle allocations in reverse order
+    for (size_t i = new_block->alloc_buffers.size(); i > 0; --i) {
+      const Buffer& buffer = new_block->alloc_buffers[i - 1];
+      body = MakeAllocStmt(buffer, std::move(body));
+    }
+    return body;
+  }
+
+  Stmt VisitStmt_(const ForNode* op) final {
+    // Step 1. Update unit loop info.
+    PrimExpr min = this->VisitExpr(op->min);
+    PrimExpr extent = this->VisitExpr(op->extent);
+    if (is_one(extent) && op->annotations.empty()) {
+      // handling unit loop
+      unit_loop_vars_[op->loop_var] = min;
+    }
+    // Step 2. Visit recursively
+    Stmt body = this->VisitStmt(op->body);
+    // Step 3. Create new For loop accordingly
+    if (op->kind == ForKind::kThreadBinding) {
+      // Case 1. Thread binding
+      ICHECK(op->thread_binding.defined());
+      String thread_tag = op->thread_binding.value()->thread_tag;
+      body = MakeLaunchThread(min, extent, op->loop_var, thread_tag, body);
+    } else if (is_one(extent) && op->annotations.empty()) {
+      // Case 2. Unit loop
+      return body;
+    } else {
+      // Case 3. An ordinary loop
+      body = For(op->loop_var, std::move(min), std::move(extent), op->kind, std::move(body));
+    }
+    // Step 4. Handle annotations
+    for (const auto& annotation : op->annotations) {
+      const String& ann_key = annotation.first;
+      const ObjectRef& ann_value = annotation.second;
+      if (attr::IsPragmaKey(ann_key)) {
+        body = AttrStmt(op->loop_var, ann_key, Downcast<PrimExpr>(ann_value), std::move(body));
+      }
+    }
+    return body;
+  }
+
+  Stmt VisitStmt_(const BufferStoreNode* op) final {
+    BufferStore store = Downcast<BufferStore>(StmtExprMutator::VisitStmt_(op));
+    return store->buffer.vstore(store->indices, store->value);
+  }
+
+  PrimExpr VisitExpr_(const VarNode* op) final {
+    Var var = GetRef<Var>(op);
+    auto it = unit_loop_vars_.find(var);
+    if (it == unit_loop_vars_.end()) {
+      return std::move(var);
+    } else {
+      return it->second;
+    }
+  }
+
+  PrimExpr VisitExpr_(const BufferLoadNode* op) final {
+    BufferLoad load = Downcast<BufferLoad>(StmtExprMutator::VisitExpr_(op));
+    return load->buffer.vload(load->indices, load->dtype);
+  }
+
+  static Stmt MakeAllocStmt(const Buffer& buffer, Stmt body) {
+    String storage_scope = buffer->scope;
+    if (storage_scope.empty()) {
+      storage_scope = "global";
+    }
+    PrimExpr area = BufferArea(buffer);
+    body = Allocate(buffer->data, buffer->dtype, {area}, const_true(), std::move(body));
+    body = AttrStmt(buffer->data, attr::storage_scope, StringImm(storage_scope), std::move(body));
+    return body;
+  }
+
+  static Stmt MakeLaunchThread(PrimExpr min, PrimExpr extent, Var var, String thread_tag,
+                               Stmt body) {
+    IterVar iter_var(/*dom=*/Range::FromMinExtent(min, extent),
+                     /*var=*/std::move(var),
+                     /*iter_type=*/IterVarType::kThreadIndex,
+                     /*thread_tag=*/thread_tag);
+    String attr_key = thread_tag == "vthread" ? attr::virtual_thread : attr::thread_extent;
+    return AttrStmt(/*node=*/std::move(iter_var),
+                    /*attr_key=*/std::move(attr_key),
+                    /*value=*/std::move(extent),
+                    /*body=*/std::move(body));
+  }
+
+  /*! \brief Record the loop_var and loop start value of unit loops, whose extent is one. */
+  std::unordered_map<Var, PrimExpr, ObjectPtrHash, ObjectPtrEqual> unit_loop_vars_;
+};
+
+PrimFunc FlattenBuffer(PrimFunc f) {
+  PrimFuncNode* fptr = f.CopyOnWrite();
+  fptr->body = BufferFlattener::Flatten(f);
+  return f;
+}
+
+namespace transform {
+
+Pass FlattenBuffer() {
+  auto pass_func = [=](PrimFunc f, IRModule m, PassContext ctx) {
+    return FlattenBuffer(std::move(f));
+  };
+  return CreatePrimFuncPass(pass_func, 0, "tir.FlattenBuffer", {});
+}
+
+TVM_REGISTER_GLOBAL("tir.transform.FlattenBuffer").set_body_typed(FlattenBuffer);
+}  // namespace transform
+
+}  // namespace tir
+}  // namespace tvm