gemini-code-assist[bot] commented on code in PR #18874:
URL: https://github.com/apache/tvm/pull/18874#discussion_r2885797582
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src/tir/transform/lower_tvm_builtin.cc:
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@@ -212,10 +220,26 @@ class BuiltinLower : public StmtExprMutator {
}
}
- Stmt VisitStmt_(const LetStmtNode* op) final {
+ Stmt VisitStmt_(const SeqStmtNode* op) final {
+ Stmt result = StmtExprMutator::VisitStmt_(op);
+ if (!pending_nd_frees_.empty()) {
+ const auto* seq = result.as<SeqStmtNode>();
+ if (seq) {
+ ffi::Array<Stmt> new_seq(seq->seq.begin(), seq->seq.end());
+ for (const auto& free_stmt : pending_nd_frees_) {
+ new_seq.push_back(free_stmt);
+ }
+ pending_nd_frees_.clear();
+ return SeqStmt(new_seq);
+ }
+ }
+ return result;
+ }
Review Comment:
The use of `pending_nd_frees_` to handle `nd_mem_alloc_with_scope`
deallocations is flawed. By pushing `free` statements to a global list and
appending them to the nearest enclosing `SeqStmt`, the pass may incorrectly
hoist a `free` call out of a conditional branch (e.g., an `IfThenElse` block).
If the allocation was conditional but the `free` is now unconditional and
outside that branch, it will lead to a free of an uninitialized or null pointer
if the allocation branch was not taken. This can result in memory corruption or
a crash on the target device. Additionally, if a `Bind` with an allocation is
not directly inside a `SeqStmt`, the `free` call might be lost or appended to
an unrelated `SeqStmt` later in the function.
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