tlopex commented on code in PR #18491:
URL: https://github.com/apache/tvm/pull/18491#discussion_r2570555092
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src/relax/backend/vm/vm_shape_lower.cc:
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@@ -399,6 +399,23 @@ class VMShapeLowerMutator
return ffi::GetRef<Expr>(op);
}
+ // Check if all expressions are computed if not mark variables as ready
and trigger computation
+ for (const PrimExpr& expr : op->values) {
+ if (!expr->IsInstance<IntImmNode>()) {
+ auto it = slot_map_.find(expr);
+ if (it != slot_map_.end() && !it->second->value_computed) {
+ // If it's a variable, mark it as ready for computation
+ if (expr.as<tir::VarNode>()) {
+ it->second->value_computed = true;
Review Comment:
Marking arbitrary tir::VarNode instances as `value_computed = true` in
`VisitExpr_` is incorrect. In VMShapeLower, only Relax ShapeVars (from function
parameters/match_cast) or IntImm constants can be safely marked as computed,
because only these have runtime values accessible to the VM.
I think correct way is to fix this earlier in the pipeline (shape
inference/canonicalization) by symbolizing composite PrimExpr (introduce Relax
ShapeVars) or simplifying them before VMShapeLower.
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