[llvm] [SCEV] Fix exit condition for recursive loop guard collection (PR #120442)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-analysis

Author: Julian Nagele (juliannagele)

<details>
<summary>Changes</summary>

When assumptions are present `Terms.size()` does not actually count the number of conditions collected from dominating branches; introduce a separate counter.

---
Full diff: https://github.com/llvm/llvm-project/pull/120442.diff


1 Files Affected:

- (modified) llvm/lib/Analysis/ScalarEvolution.cpp (+2-1) 


``````````diff
diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index d55d09020fc147..6ba91c4417f724 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -15753,6 +15753,7 @@ void ScalarEvolution::LoopGuards::collectFromBlock(
   // predecessors that can be found that have unique successors leading to the
   // original header.
   // TODO: share this logic with isLoopEntryGuardedByCond.
+  unsigned NumCollectedConditions = 0;
   std::pair<const BasicBlock *, const BasicBlock *> Pair(Pred, Block);
   for (; Pair.first;
        Pair = SE.getPredecessorWithUniqueSuccessorForBB(Pair.first)) {
@@ -15767,7 +15768,7 @@ void ScalarEvolution::LoopGuards::collectFromBlock(
 
     // If we are recursively collecting guards stop after 2
     // predecessors to limit compile-time impact for now.
-    if (Depth > 0 && Terms.size() == 2)
+    if (Depth > 0 && ++NumCollectedConditions == 2)
       break;
   }
   // Finally, if we stopped climbing the predecessor chain because

``````````

</details>


https://github.com/llvm/llvm-project/pull/120442