masahi commented on code in PR #13710:
URL: https://github.com/apache/tvm/pull/13710#discussion_r1063815756
##########
src/tir/ir/data_type_rewriter.cc:
##########
@@ -107,6 +107,26 @@ Stmt DataTypeLegalizer::VisitStmt_(const AttrStmtNode* op)
{
return StmtExprMutator::VisitStmt_(op);
}
+Stmt DataTypeLegalizer::VisitStmt_(const LetStmtNode* op) {
+ PrimExpr value = this->VisitExpr(op->value);
+ Stmt body = this->VisitStmt(op->body);
+ if (value.same_as(op->value) && body.same_as(op->body)) {
+ return GetRef<Stmt>(op);
+ } else if (value.dtype() == op->var->dtype) {
+ auto n = CopyOnWrite(op);
+ n->value = std::move(value);
+ n->body = std::move(body);
+ return Stmt(n);
+ } else {
+ auto new_var = op->var.copy_with_dtype(value.dtype());
+ Map<Var, PrimExpr> vmap{{op->var, new_var}};
+ auto new_body = SubstituteWithDataTypeLegalization(
+ std::move(body), [&](const Var& var) { return vmap.Get(var); });
+ // We need to visit the body again to insert additional casts
Review Comment:
We can pass `op->body` to `SubstituteWithDataTypeLegalization`, but we still
need to visit `new_body` after `SubstituteWithDataTypeLegalization`. In that
case, the output of the first visit,`this->VisitStmt(op->body)` at the top is
only used for the first two `if / else` branches.
So this doesn't work, because the body of the Let has outdated variable
dtype. Is this your understanding as well, or are you suggesting something else?
```
auto new_body = SubstituteWithDataTypeLegalization(
std::move(op->body), [&](const Var& var) { return vmap.Get(var); });
// We need to visit the body again to insert additional casts
return LetStmt(new_var, value, new_body, op->span);
```
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