llvm-project

5d111a20 - [DAGCombiner] Avoid double deletion when replacing multiple frozen/unfrozen uses (#155427)

[DAGCombiner] Avoid double deletion when replacing multiple frozen/unfrozen uses (#155427) Closes https://github.com/llvm/llvm-project/issues/155345. In the original case, we have one frozen use and two unfrozen uses: ``` t73: i8 = select t81, Constant:i8<0>, t18 t75: i8 = select t10, t18, t73 t59: i8 = freeze t18 (combining) t80: i8 = freeze t59 (another user of t59) ``` In `DAGCombiner::visitFREEZE`, we replace all uses of `t18` with `t59`. After updating the uses, `t59: i8 = freeze t18` will be updated to `t59: i8 = freeze t59` (`AddModifiedNodeToCSEMaps`) and CSEed into `t80: i8 = freeze t59` (`ReplaceAllUsesWith`). As the previous call to `AddModifiedNodeToCSEMaps` already removed `t59` from the CSE map, `ReplaceAllUsesWith` cannot remove `t59` again. For clarity, see the following call graph: ``` ReplaceAllUsesOfValueWith(t18, t59) ReplaceAllUsesWith(t18, t59) RemoveNodeFromCSEMaps(t73) update t73 AddModifiedNodeToCSEMaps(t73) RemoveNodeFromCSEMaps(t75) update t75 AddModifiedNodeToCSEMaps(t75) RemoveNodeFromCSEMaps(t59) <- first delection update t59 AddModifiedNodeToCSEMaps(t59) ReplaceAllUsesWith(t59, t80) RemoveNodeFromCSEMaps(t59) <- second delection Boom! ``` This patch unfreezes all the uses first to avoid triggering CSE when introducing cycles.