Revert "[StructurizeCFG] Refactor insertConditions. NFC. (llvm#115476)" (llvm#136370) (llvm#3176)

Author: vamovsik

llvm/lib/Transforms/Scalar/StructurizeCFG.cpp

@@ -614,25 +614,28 @@ void StructurizeCFG::insertConditions(bool Loops) {
     BasicBlock *SuccTrue = Term->getSuccessor(0);
     BasicBlock *SuccFalse = Term->getSuccessor(1);
 
-    BBPredicates &Preds = Loops ? LoopPreds[SuccFalse] : Predicates[SuccTrue];
+    PhiInserter.Initialize(Boolean, "");
+    PhiInserter.AddAvailableValue(Loops ? SuccFalse : Parent, Default);
 
-    if (Preds.size() == 1 && Preds.begin()->first == Parent) {
-      auto &PI = Preds.begin()->second;
-      Term->setCondition(PI.Pred);
-      CondBranchWeights::setMetadata(*Term, PI.Weights);
-    } else {
-      PhiInserter.Initialize(Boolean, "");
-      PhiInserter.AddAvailableValue(Loops ? SuccFalse : Parent, Default);
+    BBPredicates &Preds = Loops ? LoopPreds[SuccFalse] : Predicates[SuccTrue];
 
-      NearestCommonDominator Dominator(DT);
-      Dominator.addBlock(Parent);
+    NearestCommonDominator Dominator(DT);
+    Dominator.addBlock(Parent);
 
-      for (auto [BB, PI] : Preds) {
-        assert(BB != Parent);
-        PhiInserter.AddAvailableValue(BB, PI.Pred);
-        Dominator.addAndRememberBlock(BB);
+    PredInfo ParentInfo{nullptr, std::nullopt};
+    for (auto [BB, PI] : Preds) {
+      if (BB == Parent) {
+        ParentInfo = PI;
+        break;
       }
+      PhiInserter.AddAvailableValue(BB, PI.Pred);
+      Dominator.addAndRememberBlock(BB);
+    }
 
+    if (ParentInfo.Pred) {
+      Term->setCondition(ParentInfo.Pred);
+      CondBranchWeights::setMetadata(*Term, ParentInfo.Weights);
+    } else {
       if (!Dominator.resultIsRememberedBlock())
         PhiInserter.AddAvailableValue(Dominator.result(), Default);
 

llvm/test/Transforms/StructurizeCFG/simple-structurizecfg-crash.ll

@@ -0,0 +1,28 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt -S -passes=structurizecfg %s -o - | FileCheck %s
+
+; Issue tracking: https://github.com/llvm/llvm-project/issues/126534.
+
+define void @foo() {
+; CHECK-LABEL: define void @foo() {
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    br label %[[COND_FALSE:.*]]
+; CHECK:       [[COND_TRUE:.*]]:
+; CHECK-NEXT:    br label %[[COND_END:.*]]
+; CHECK:       [[COND_FALSE]]:
+; CHECK-NEXT:    br i1 false, label %[[COND_TRUE]], label %[[COND_END]]
+; CHECK:       [[COND_END]]:
+; CHECK-NEXT:    ret void
+;
+entry:
+  br i1 false, label %cond.true, label %cond.false
+
+cond.true:                                        ; preds = %entry
+  br label %cond.end
+
+cond.false:                                       ; preds = %entry
+  br label %cond.end
+
+cond.end:                                         ; preds = %cond.false, %cond.true
+  ret void
+}