[SimplifyCFG] removeUnreachableBlocks() already knows how to preserve…

… DomTree ... so just ensure that we pass DomTreeUpdater it into it. Apparently, there were no dedicated tests just for that functionality, so i'm adding one here.
YuriPlyakhin · Dec 16, 2020 · 4fc169f · 4fc169f
1 parent aa2009f
commit 4fc169f
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Showing 2 changed files with 22 additions and 3 deletions.
diff --git a/llvm/lib/Transforms/Scalar/SimplifyCFGPass.cpp b/llvm/lib/Transforms/Scalar/SimplifyCFGPass.cpp
@@ -25,6 +25,7 @@
 #include "llvm/ADT/Statistic.h"
 #include "llvm/Analysis/AssumptionCache.h"
 #include "llvm/Analysis/CFG.h"
+#include "llvm/Analysis/DomTreeUpdater.h"
 #include "llvm/Analysis/GlobalsModRef.h"
 #include "llvm/Analysis/TargetTransformInfo.h"
 #include "llvm/IR/Attributes.h"
@@ -195,7 +196,9 @@ static bool iterativelySimplifyCFG(Function &F, const TargetTransformInfo &TTI,
 static bool simplifyFunctionCFGImpl(Function &F, const TargetTransformInfo &TTI,
                                     DominatorTree *DT,
                                     const SimplifyCFGOptions &Options) {
-  bool EverChanged = removeUnreachableBlocks(F);
+  DomTreeUpdater DTU(DT, DomTreeUpdater::UpdateStrategy::Eager);
+
+  bool EverChanged = removeUnreachableBlocks(F, DT ? &DTU : nullptr);
   EverChanged |= mergeEmptyReturnBlocks(F);
   EverChanged |= iterativelySimplifyCFG(F, TTI, Options);
 
@@ -207,12 +210,12 @@ static bool simplifyFunctionCFGImpl(Function &F, const TargetTransformInfo &TTI,
   // iterate between the two optimizations.  We structure the code like this to
   // avoid rerunning iterativelySimplifyCFG if the second pass of
   // removeUnreachableBlocks doesn't do anything.
-  if (!removeUnreachableBlocks(F))
+  if (!removeUnreachableBlocks(F, DT ? &DTU : nullptr))
     return true;
 
   do {
     EverChanged = iterativelySimplifyCFG(F, TTI, Options);
-    EverChanged |= removeUnreachableBlocks(F);
+    EverChanged |= removeUnreachableBlocks(F, DT ? &DTU : nullptr);
   } while (EverChanged);
 
   return true;

diff --git a/llvm/test/Transforms/SimplifyCFG/unreachable-selfloop.ll b/llvm/test/Transforms/SimplifyCFG/unreachable-selfloop.ll
@@ -0,0 +1,16 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -simplifycfg -simplifycfg-require-and-preserve-domtree=1 -S < %s | FileCheck %s
+
+define void @fn() {
+; CHECK-LABEL: @fn(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    ret void
+;
+entry:
+  ret void
+
+unreachable_bb0:
+  br label %unreachable_bb1
+unreachable_bb1:
+  br label %unreachable_bb0
+}