[llvm] [SimplifyCFG] Check whether the previous condition is true before making assume (PR #105986)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-transforms

Author: None (GkvJwa)

<details>
<summary>Changes</summary>

Fixes #<!-- -->105985

---
Full diff: https://github.com/llvm/llvm-project/pull/105986.diff


1 Files Affected:

- (modified) llvm/lib/Transforms/Utils/SimplifyCFG.cpp (+9) 


``````````diff
diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index da4d57f808e9bf..32f76cfc5818d3 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -7852,6 +7852,15 @@ static bool removeUndefIntroducingPredecessor(BasicBlock *BB,
         Instruction *T = Predecessor->getTerminator();
         IRBuilder<> Builder(T);
         if (BranchInst *BI = dyn_cast<BranchInst>(T)) {
+          // Prevent multiple conditions cases
+          if (dyn_cast<CmpInst>(BI->getCondition()) &&
+              !pred_empty(Predecessor)) {
+            BranchInst *Pred_BI = dyn_cast<BranchInst>(
+                (*pred_begin(Predecessor))->getTerminator());
+            if (Pred_BI && dyn_cast<CmpInst>(BI->getCondition())) {
+              continue;
+            }
+          }
           BB->removePredecessor(Predecessor);
           // Turn unconditional branches into unreachables and remove the dead
           // destination from conditional branches.

``````````

</details>


https://github.com/llvm/llvm-project/pull/105986