[llvm] 262ff9c - [SimplifyCFG] Teach TryToMergeLandingPad() to preserve DomTree

[Roman Lebedev via llvm-commits]

Author: Roman Lebedev
Date: 2020-12-20T00:18:36+03:00
New Revision: 262ff9c23e72643ba02db6166b6ca942ef067dc9

URL: https://github.com/llvm/llvm-project/commit/262ff9c23e72643ba02db6166b6ca942ef067dc9
DIFF: https://github.com/llvm/llvm-project/commit/262ff9c23e72643ba02db6166b6ca942ef067dc9.diff

LOG: [SimplifyCFG] Teach TryToMergeLandingPad() to preserve DomTree

Added: 
    

Modified: 
    llvm/lib/Transforms/Utils/SimplifyCFG.cpp
    llvm/test/Transforms/SimplifyCFG/duplicate-landingpad.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index 3bc09978489e..c2557165a0ba 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -6082,7 +6082,7 @@ bool SimplifyCFGOpt::simplifyIndirectBr(IndirectBrInst *IBI) {
 /// block when the inputs in the phi are the same for the two blocks being
 /// merged.  In some cases, this could result in removal of the PHI entirely.
 static bool TryToMergeLandingPad(LandingPadInst *LPad, BranchInst *BI,
-                                 BasicBlock *BB) {
+                                 BasicBlock *BB, DomTreeUpdater *DTU) {
   auto Succ = BB->getUniqueSuccessor();
   assert(Succ);
   // If there's a phi in the successor block, we'd likely have to introduce
@@ -6103,6 +6103,8 @@ static bool TryToMergeLandingPad(LandingPadInst *LPad, BranchInst *BI,
     if (!BI2 || !BI2->isIdenticalTo(BI))
       continue;
 
+    std::vector<DominatorTree::UpdateType> Updates;
+
     // We've found an identical block.  Update our predecessors to take that
     // path instead and make ourselves dead.
     SmallPtrSet<BasicBlock *, 16> Preds;
@@ -6112,6 +6114,8 @@ static bool TryToMergeLandingPad(LandingPadInst *LPad, BranchInst *BI,
       assert(II->getNormalDest() != BB && II->getUnwindDest() == BB &&
              "unexpected successor");
       II->setUnwindDest(OtherPred);
+      Updates.push_back({DominatorTree::Delete, Pred, BB});
+      Updates.push_back({DominatorTree::Insert, Pred, OtherPred});
     }
 
     // The debug info in OtherPred doesn't cover the merged control flow that
@@ -6127,11 +6131,14 @@ static bool TryToMergeLandingPad(LandingPadInst *LPad, BranchInst *BI,
     Succs.insert(succ_begin(BB), succ_end(BB));
     for (BasicBlock *Succ : Succs) {
       Succ->removePredecessor(BB);
+      Updates.push_back({DominatorTree::Delete, BB, Succ});
     }
 
     IRBuilder<> Builder(BI);
     Builder.CreateUnreachable();
     BI->eraseFromParent();
+    if (DTU)
+      DTU->applyUpdatesPermissive(Updates);
     return true;
   }
   return false;
@@ -6179,7 +6186,7 @@ bool SimplifyCFGOpt::simplifyUncondBranch(BranchInst *BI,
   if (LandingPadInst *LPad = dyn_cast<LandingPadInst>(I)) {
     for (++I; isa<DbgInfoIntrinsic>(I); ++I)
       ;
-    if (I->isTerminator() && TryToMergeLandingPad(LPad, BI, BB))
+    if (I->isTerminator() && TryToMergeLandingPad(LPad, BI, BB, DTU))
       return true;
   }
 

diff  --git a/llvm/test/Transforms/SimplifyCFG/duplicate-landingpad.ll b/llvm/test/Transforms/SimplifyCFG/duplicate-landingpad.ll
index 6f8b069810f8..a38f0ae6275c 100644
--- a/llvm/test/Transforms/SimplifyCFG/duplicate-landingpad.ll
+++ b/llvm/test/Transforms/SimplifyCFG/duplicate-landingpad.ll
@@ -1,5 +1,5 @@
 ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
-; RUN: opt < %s -simplifycfg -S | FileCheck %s
+; RUN: opt < %s -simplifycfg -simplifycfg-require-and-preserve-domtree=1 -S | FileCheck %s
 target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
 
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