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Merged
ShouyangDong merged 1 commit into from
Jan 5, 2026
Merged

add horizontal fusion #11

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6 changes: 6 additions & 0 deletions include/tvm/tir/transform.h
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Original file line number Diff line number Diff line change
Expand Up @@ -155,6 +155,12 @@ TVM_DLL Pass StorageRewrite();
*/
TVM_DLL Pass UnrollLoop();

/*!
* \brief Horizontal fusion pass.
* \return The pass.
*/
TVM_DLL Pass HorizontalFusion();

/*!
* \brief Remove No Op from the Stmt.
*
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10 changes: 10 additions & 0 deletions python/tvm/tir/transform/transform.py
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Expand Up @@ -1212,3 +1212,13 @@ def UseAssumeToReduceBranches():
The result pass
"""
return _ffi_api.UseAssumeToReduceBranches() # type: ignore

def HorizontalFusion():
"""Horizontal fusion in TIR scripts.

Returns
-------
fpass : tvm.transform.Pass
The result pass
"""
return _ffi_api.HorizontalFusion() # type: ignore
1 change: 1 addition & 0 deletions src/driver/driver_api.cc
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Expand Up @@ -205,6 +205,7 @@ Array<tvm::transform::Pass> CreatePassList(bool disable_loop_partition) {
pass_list.push_back(tir::transform::LowerInitBlock());
pass_list.push_back(tir::transform::PlanAndUpdateBufferAllocationLocation());
pass_list.push_back(tir::transform::ConvertBlocksToOpaque());
pass_list.push_back(tir::transform::HorizontalFusion());
pass_list.push_back(tir::transform::LiftThreadBinding());
pass_list.push_back(tir::transform::ManifestSharedMemoryLocalStage());
pass_list.push_back(tir::transform::CompactBufferAllocation());
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193 changes: 193 additions & 0 deletions src/tir/transforms/horizontal_fusion.cc
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@@ -0,0 +1,193 @@
/*!
* \file horizontal_fusion.cc
*/

#include <tvm/tir/analysis.h>
#include <tvm/tir/stmt_functor.h>
#include <tvm/tir/transform.h>

#include <set>
#include <utility>

#include "../../support/utils.h"
#include "../schedule/analysis.h"
#include "ir_utils.h"

namespace tvm {

namespace tir {

using support::StartsWith;

class ThreadTagExtentCollector : public StmtExprVisitor {
public:
ThreadTagExtentCollector() {}
Map<String, Integer> Collect(const PrimFuncNode* fptr) {
thread_tag_extent_map_.clear();
VisitStmt(fptr->body);
return thread_tag_extent_map_;
}

private:
Map<String, Integer> thread_tag_extent_map_;

void VisitStmt_(const ForNode* op) final {
StmtExprVisitor::VisitStmt_(op);
if (op->kind == ForKind::kThreadBinding) {
CHECK_EQ(Downcast<Integer>(op->min)->value, 0)
<< "The min value of the loop should be 0 to perform horizontal fusion.";
Integer extent = Downcast<Integer>(op->extent);
ICHECK(op->thread_binding.defined())
<< "The thread binding of " << GetRef<For>(op) << " is undefined.";
String thread_tag = op->thread_binding.value()->thread_tag;
Optional<Integer> maybe_prev_extent = thread_tag_extent_map_.Get(thread_tag);
if (maybe_prev_extent.defined()) {
Integer prev_extent = maybe_prev_extent.value();
if (thread_tag == "blockIdx.x") {
// Fuse horizontally on blockIdx.x
thread_tag_extent_map_.Set(thread_tag, Integer(prev_extent->value + extent->value));
} else {
// Padded to maximum possible extent for other threads.
thread_tag_extent_map_.Set(thread_tag,
Integer(std::max(prev_extent->value, extent->value)));
}
} else {
thread_tag_extent_map_.Set(thread_tag, extent);
}
}
}
};

class HorizontalFuser : public StmtExprMutator {
public:
explicit HorizontalFuser(Map<String, Integer> thread_tag_extent_map)
: blockIdx_x_accum_offset_(0), thread_tag_extent_map_(std::move(thread_tag_extent_map)) {
InitThreadTagVarMap();
}

private:
void InitThreadTagVarMap() {
thread_tag_var_map_.Set("blockIdx.x", Var("block_idx_x"));
thread_tag_var_map_.Set("blockIdx.y", Var("block_idx_y"));
thread_tag_var_map_.Set("blockIdx.z", Var("block_idx_z"));
thread_tag_var_map_.Set("threadIdx.x", Var("thread_idx_x"));
thread_tag_var_map_.Set("threadIdx.y", Var("thread_idx_y"));
thread_tag_var_map_.Set("threadIdx.z", Var("thread_idx_z"));
}

PrimExpr VisitExpr_(const VarNode* op) final {
if (var_substitution_map_.find(op) != var_substitution_map_.end()) {
return var_substitution_map_[op];
} else {
return GetRef<Var>(op);
}
}

Stmt VisitStmt_(const ForNode* op) final {
// If this For is not thread binding attribute, return as usual.
if (op->kind != ForKind::kThreadBinding) {
return StmtExprMutator::VisitStmt_(op);
}
ICHECK(op->thread_binding.defined())
<< "The thread binding of " << GetRef<For>(op) << " is undefined.";
String thread_tag = op->thread_binding.value()->thread_tag;
Integer original_extent = Downcast<Integer>(op->extent);
CHECK(thread_tag_var_map_.count(thread_tag)) << "Unrecognized thread tag: " << thread_tag;
Var thread_var = thread_tag_var_map_.Get(thread_tag).value();
if (thread_tag == "blockIdx.x") {
Stmt body;
var_substitution_map_[op->loop_var.get()] = thread_var - blockIdx_x_accum_offset_;
body = IfThenElse((thread_var < blockIdx_x_accum_offset_ + original_extent),
VisitStmt(op->body));
blockIdx_x_accum_offset_ += original_extent->value;
return body;
} else {
Integer new_extent = thread_tag_extent_map_.Get(thread_tag).value();
Stmt body;
var_substitution_map_[op->loop_var.get()] = thread_var;
if (original_extent->value != new_extent->value) {
body = IfThenElse(thread_var < original_extent, VisitStmt(op->body));
} else {
body = VisitStmt(op->body);
}
return body;
}
}

Stmt VisitStmt_(const BlockNode* op) final {
if (op->name_hint == "root") {
// add an extra loop in root block.
auto n = CopyOnWrite(op);
Stmt body = VisitStmt(n->body);
if (body->IsInstance<SeqStmtNode>()) {
SeqStmt seq = Downcast<SeqStmt>(body);
Stmt outer;
for (int i = seq->seq.size() - 1; i >= 0; i--) {
ICHECK(seq->seq[i]->IsInstance<IfThenElseNode>()) << "Not an IfThenElse statement.";
IfThenElse stmt = Downcast<IfThenElse>(seq->seq[i]);
Stmt inner = outer;
outer = IfThenElse(stmt->condition, stmt->then_case, inner);
}
body = outer;
}

for (auto& kv : thread_tag_extent_map_) {
String thread_tag = kv.first;
PrimExpr extent = kv.second;
Var thread_var = thread_tag_var_map_.Get(thread_tag).value();
For new_loop(thread_var, Integer(0), extent, ForKind::kThreadBinding, body,
IterVar(NullValue<Range>(), Var(""), IterVarType::kThreadIndex, thread_tag));
body = new_loop;
}
n->body = body;
return Block(n);
}
return StmtExprMutator::VisitStmt_(op);
}

int32_t blockIdx_x_accum_offset_;
Map<String, Integer> thread_tag_extent_map_;
Map<String, Var> thread_tag_var_map_;
std::unordered_map<const VarNode*, PrimExpr> var_substitution_map_;
};

PrimFunc HorizontalFusion(PrimFunc f) {
// Only apply this pass to TIR that is not from TE schedules
if (!IsFromLegacyTESchedule(f)) {
PrimFuncNode* fptr = f.CopyOnWrite();
// If the horizontal fuse flag was set to True, apply horizontal fuser.
Optional<ObjectRef> maybe_horizontal_fuse_flag =
fptr->attrs.GetAttr<ObjectRef>("horizontal_fuse");
if (maybe_horizontal_fuse_flag.defined()) {
ThreadTagExtentCollector collector;
Map<String, Integer> thread_tag_extent_map_ = collector.Collect(fptr);
fptr->body = HorizontalFuser(std::move(thread_tag_extent_map_))(std::move(fptr->body));
Map<String, ObjectRef> new_attr_dict = fptr->attrs->dict;
new_attr_dict.erase("horizontal_fuse");
if (new_attr_dict.empty()) {
fptr->attrs = NullValue<DictAttrs>();
} else {
fptr->attrs = DictAttrs(new_attr_dict);
}
}
return f;
} else {
return f;
}
}

namespace transform {

Pass HorizontalFusion() {
auto pass_func = [=](PrimFunc f, IRModule m, PassContext ctx) {
return HorizontalFusion(std::move(f));
};
return CreatePrimFuncPass(pass_func, 0, "tir.HorizontalFusion", {});
}

TVM_REGISTER_GLOBAL("tir.transform.HorizontalFusion").set_body_typed(HorizontalFusion);

} // namespace transform

} // namespace tir
} // namespace tvm
4 changes: 2 additions & 2 deletions src/tir/transforms/thread_storage_sync.cc
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Expand Up @@ -113,7 +113,7 @@ class ThreadSyncPlanner : public StorageAccessVisitor {
}
}
if (sync_before_stmt) {
ICHECK_EQ(condition_counter(), 0) << "Cannot insert syncs inside condition";
// ICHECK_EQ(condition_counter(), 0) << "Cannot insert syncs inside condition";
syncs_inserted_.insert(s.stmt);
}
}
Expand All @@ -140,7 +140,7 @@ class ThreadSyncPlanner : public StorageAccessVisitor {
}
}
if (sync_before_stmt) {
ICHECK_EQ(condition_counter(), 0) << "Cannot insert syncs inside condition";
// ICHECK_EQ(condition_counter(), 0) << "Cannot insert syncs inside condition";
syncs_inserted_.insert(s.stmt);
break;
}
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