[SimplifyCFG] Teach SimplifyEqualityComparisonWithOnlyPredecessor() to preserve DomTree, part 2

llvm/lib/Transforms/Utils/SimplifyCFG.cpp

@@ -970,12 +970,15 @@ bool SimplifyCFGOpt::SimplifyEqualityComparisonWithOnlyPredecessor(
   if (!TheRealDest)
     TheRealDest = ThisDef;
 
+  SmallVector<DominatorTree::UpdateType, 2> Updates;
+
   // Remove PHI node entries for dead edges.
   BasicBlock *CheckEdge = TheRealDest;
   for (BasicBlock *Succ : successors(TIBB))
-    if (Succ != CheckEdge)
+    if (Succ != CheckEdge) {
       Succ->removePredecessor(TIBB);
-    else
+      Updates.push_back({DominatorTree::Delete, TIBB, Succ});
+    } else
       CheckEdge = nullptr;
 
   // Insert the new branch.
@@ -987,6 +990,8 @@ bool SimplifyCFGOpt::SimplifyEqualityComparisonWithOnlyPredecessor(
                     << "\n");
 
   EraseTerminatorAndDCECond(TI);
+  if (DTU)
+    DTU->applyUpdatesPermissive(Updates);
   return true;
 }
 

llvm/test/Transforms/SimplifyCFG/InfLoop.ll

@@ -1,4 +1,4 @@
-; RUN: opt < %s -simplifycfg -disable-output
+; RUN: opt < %s -simplifycfg -simplifycfg-require-and-preserve-domtree=1 -disable-output
 ; END.
 
 target datalayout = "e-m:o-p:32:32-f64:32:64-v64:32:64-v128:32:128-a:0:32-n32-S32"

llvm/test/Transforms/SimplifyCFG/implied-cond-matching-imm.ll

@@ -1,4 +1,4 @@
-; RUN: opt %s -S -simplifycfg | FileCheck %s
+; RUN: opt %s -S -simplifycfg -simplifycfg-require-and-preserve-domtree=1 | FileCheck %s
 
 ; cmp1 implies cmp2 is false
 ; CHECK-LABEL: @test1

llvm/test/Transforms/SimplifyCFG/iterative-simplify.ll

@@ -1,4 +1,4 @@
-; RUN: opt < %s -simplifycfg -S | not grep bb17
+; RUN: opt < %s -simplifycfg -simplifycfg-require-and-preserve-domtree=1 -S | not grep bb17
 ; PR1786
 
 define i32 @main() {