[llvm] [DAGCombiner] Limit steps in shouldCombineToPostInc (PR #116030)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-selectiondag

Author: Jonathan Cohen (jcohen-apple)

<details>
<summary>Changes</summary>

Currently the function will walk the entire DAG to find other candidates to perform a post-inc store. This leads to very long compilation times on large functions. Added a MaxSteps limit to avoid this, which is also aligned to how hasPredecessorHelper is used elsewhere in the code.

---
Full diff: https://github.com/llvm/llvm-project/pull/116030.diff


1 Files Affected:

- (modified) llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp (+2-1) 


``````````diff
diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 6059229cd6d9a4..cc51aed40003f0 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -19089,7 +19089,8 @@ static bool shouldCombineToPostInc(SDNode *N, SDValue Ptr, SDNode *PtrUse,
                                    IsMasked, OtherPtr, TLI)) {
         SmallVector<const SDNode *, 2> Worklist;
         Worklist.push_back(Use);
-        if (SDNode::hasPredecessorHelper(N, Visited, Worklist))
+        constexpr unsigned int MaxSteps = 8192;
+        if (SDNode::hasPredecessorHelper(N, Visited, Worklist, MaxSteps))
           return false;
       }
     }

``````````

</details>


https://github.com/llvm/llvm-project/pull/116030