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

[via llvm-commits]

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

>From ef85b6718b84aeefea28301c0e2a338317ed5625 Mon Sep 17 00:00:00 2001
From: GkvJwa <gkvjwa at gmail.com>
Date: Sun, 25 Aug 2024 23:36:11 +0800
Subject: [PATCH] [SimplifyCFG] Check whether the previous condition is true
 before making assume

---
 llvm/lib/Transforms/Utils/SimplifyCFG.cpp | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index da4d57f808e9bf..33556628d7a7e3 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -7852,6 +7852,16 @@ static bool removeUndefIntroducingPredecessor(BasicBlock *BB,
         Instruction *T = Predecessor->getTerminator();
         IRBuilder<> Builder(T);
         if (BranchInst *BI = dyn_cast<BranchInst>(T)) {
+          // Prevent more complex conditionals
+          if (BI->isConditional() && dyn_cast<CmpInst>(BI->getCondition()) &&
+              !pred_empty(Predecessor)) {
+            BranchInst *Pred_BI = dyn_cast<BranchInst>(
+                (*pred_begin(Predecessor))->getTerminator());
+            if (Pred_BI && BI->isConditional() &&
+                dyn_cast<CmpInst>(BI->getCondition())) {
+              continue;
+            }
+          }
           BB->removePredecessor(Predecessor);
           // Turn unconditional branches into unreachables and remove the dead
           // destination from conditional branches.