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The pass which instruments checkers before memory accesses (load/store). This allows to handle invalid memory accesses. The patch is related to issue: https://discuss.tvm.ai/t/array-bounds-checking/944
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,193 @@ | ||
| /*! | ||
| * Copyright (c) 2018 by Contributors | ||
| * \file bounds_checker.cc | ||
| */ | ||
| // Instrument checkers for out of the bounds access. | ||
|
|
||
| #include <tvm/ir.h> | ||
| #include <tvm/ir_mutator.h> | ||
| #include <tvm/ir_pass.h> | ||
| #include <tvm/ir_visitor.h> | ||
| #include <vector> | ||
| #include <unordered_map> | ||
| #include <utility> | ||
|
|
||
| namespace tvm { | ||
| namespace ir { | ||
|
|
||
| class BoundCollector : public IRVisitor { | ||
| public: | ||
| BoundCollector() {} | ||
|
|
||
| void Visit_(const AttrStmt *op) { | ||
| if (op->attr_key == ir::attr::buffer_bound) { | ||
| if (const Variable *key = op->node.as<Variable>()) { | ||
| mem_to_shape[key] = op->value; | ||
| } | ||
| } | ||
| IRVisitor::Visit_(op); | ||
| } | ||
| // Hashtable which maps buffer_var to shape. | ||
| std::unordered_map<const Variable *, Expr> mem_to_shape; | ||
| }; | ||
|
|
||
| class BoundChecker : public IRMutator { | ||
| public: | ||
| explicit BoundChecker( | ||
| const std::unordered_map<const Variable *, Expr> &mem_to_shape) | ||
| : mem_to_shape_(mem_to_shape) {} | ||
|
|
||
| Stmt Mutate_(const Allocate *op, const Stmt &s) final { | ||
| // If the shape was updated we should update the hashtable. | ||
| if (UpdateIsNeeded(op->buffer_var)) { | ||
| Update(op->buffer_var, op->extents, op->type); | ||
| } | ||
| return IRMutator::Mutate_(op, s); | ||
| } | ||
|
|
||
| Expr Mutate_(const Call *op, const Expr &ex) final { | ||
| if (process_store_ && op->is_intrinsic(intrinsic::tvm_if_then_else)) { | ||
| unsafe_rewritten_ = true; | ||
| } | ||
| return IRMutator::Mutate_(op, ex); | ||
| } | ||
|
|
||
| Stmt Mutate_(const Store *op, const Stmt &s) final { | ||
| store_scope_bound_collector_.clear(); | ||
| process_store_ = true; | ||
| unsafe_rewritten_ = false; | ||
| IRMutator::Mutate_(op, s); | ||
| process_store_ = false; | ||
| if (CanInstrument(op->index, op->buffer_var)) { | ||
| Collect(op->index, op->buffer_var); | ||
| } | ||
| // The collector should has at least one item. | ||
| if (store_scope_bound_collector_.size()) { | ||
| Expr condition = MakeCondition(); | ||
| if (!condition.as<StringImm>()) { | ||
| Stmt nop = Evaluate::make(1); | ||
| Stmt then_case = | ||
| Store::make(op->buffer_var, op->value, op->index, op->predicate); | ||
| Stmt else_case = | ||
| AssertStmt::make(condition, StringImm::make(error_message_), nop); | ||
| Stmt body = IfThenElse::make(condition, then_case, else_case); | ||
| return body; | ||
| } | ||
| } | ||
| return s; | ||
| } | ||
|
|
||
| Expr Mutate_(const Load *op, const Expr &ex) final { | ||
| if (CanInstrument(op->index, op->buffer_var)) { | ||
| Collect(op->index, op->buffer_var); | ||
| } | ||
| return IRMutator::Mutate_(op, ex); | ||
| } | ||
|
|
||
| private: | ||
| bool UpdateIsNeeded(const VarExpr &buffer_var) const { | ||
| return (buffer_var.defined() && mem_to_shape_.count(buffer_var.get())); | ||
| } | ||
|
|
||
| void Update(const VarExpr &buffer_var, const Array<Expr> &new_shape, | ||
| const Type &type) { | ||
| // Sanity check at first. | ||
| if (!new_shape.size()) | ||
| return; | ||
|
|
||
| for (size_t i = 0; i < new_shape.size(); ++i) { | ||
| if (!new_shape[0].defined() || !new_shape[i].type().is_scalar() || | ||
| is_negative_const(new_shape[i])) { | ||
| return; | ||
| } | ||
| } | ||
|
|
||
| // Scalarize the shape. | ||
| Expr shape = Mul::make(make_const(UInt(64), type.lanes()), | ||
| Cast::make(UInt(64), new_shape[0])); | ||
| for (size_t i = 1; i < new_shape.size(); ++i) { | ||
| // Cast to unsigned to avoid integer overlow at frist. | ||
| shape = Mul::make(shape, Mul::make(make_const(UInt(64), type.lanes()), | ||
| Cast::make(UInt(64), new_shape[i]))); | ||
| } | ||
| mem_to_shape_[buffer_var.get()] = shape; | ||
| } | ||
|
|
||
| bool IndexIsValid(const Expr &index) const { | ||
| if (!index.defined()) | ||
| return false; | ||
|
|
||
| if (const Ramp *ramp_index = index.as<Ramp>()) { | ||
| return ramp_index->base.defined() && | ||
| ramp_index->base.type().is_scalar() && | ||
| ramp_index->stride.defined() && | ||
| ramp_index->stride.type().is_scalar() && (ramp_index->lanes > 0); | ||
| } | ||
| return true; | ||
| } | ||
|
|
||
| bool CanInstrument(const Expr &index, const VarExpr &buffer_var) const { | ||
| return buffer_var.defined() && mem_to_shape_.count(buffer_var.get()) && | ||
| IndexIsValid(index) && !unsafe_rewritten_; | ||
| } | ||
|
|
||
| void Collect(Expr index, VarExpr buffer_var) { | ||
| store_scope_bound_collector_.push_back( | ||
| std::make_pair(index, mem_to_shape_[buffer_var.get()])); | ||
| } | ||
|
|
||
| Expr MakeCondition() { | ||
| Expr condition; | ||
| for (size_t i = 0; i < store_scope_bound_collector_.size(); ++i) { | ||
| std::pair<Expr, Expr> buffer_to_mem = store_scope_bound_collector_[i]; | ||
| Expr index = buffer_to_mem.first; | ||
| Expr upper_bound = buffer_to_mem.second; | ||
|
|
||
| if (const Ramp *ramp_index = index.as<Ramp>()) { | ||
| // In case index is base + stride * i. | ||
| // Non inclusive range. | ||
| index = Add::make( | ||
| ramp_index->base, | ||
| Mul::make(ramp_index->stride, make_const(ramp_index->stride.type(), | ||
| ramp_index->lanes - 1))); | ||
| } | ||
|
|
||
| // Try to simplify index and bound. | ||
| index = ir::Simplify(index); | ||
| upper_bound = ir::Simplify(upper_bound); | ||
|
|
||
| // Cast to the same type - signed, to be able to check lower bound. | ||
| index = Cast::make(Int(64), index); | ||
| upper_bound = Cast::make(Int(64), upper_bound); | ||
|
|
||
| // Looks like a lower bound should always be zero after normalization. | ||
| Expr lower_bound = make_zero(Int(64)); | ||
|
|
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| Expr current_condition = | ||
| And::make(GE::make(index, lower_bound), LT::make(index, upper_bound)); | ||
| condition = | ||
| !i ? current_condition : And::make(condition, current_condition); | ||
| } | ||
| return condition; | ||
| } | ||
|
|
||
| // Whether we process store value recursively. | ||
| bool process_store_{false}; | ||
| // Whether we face tvm_if_then_else intrinsic. | ||
| bool unsafe_rewritten_{false}; | ||
| // Pool which collects the pair of index and shape for specific store/load. | ||
| std::vector<std::pair<Expr, Expr>> store_scope_bound_collector_; | ||
| // Error message. | ||
| const char *const error_message_ = "OUT OF THE BOUNDS"; | ||
| // Hashtable which maps buffer_var to shape. | ||
| std::unordered_map<const Variable *, Expr> mem_to_shape_; | ||
| }; | ||
|
|
||
| Stmt InstrumentBoundCheckers(Stmt stmt) { | ||
| BoundCollector bound_collector; | ||
| // At first walk recursively and collect bound attributes. | ||
| bound_collector.Visit(stmt); | ||
| return BoundChecker(bound_collector.mem_to_shape).Mutate(stmt); | ||
| } | ||
| } // namespace ir | ||
| } // namespace tvm |
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