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[SimplifyCFG] Teach TryToMergeLandingPad() to preserve DomTree

This commit is contained in:
Roman Lebedev 2020-12-19 20:51:48 +03:00
parent 6a1617d67c
commit 262ff9c23e
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GPG Key ID: 083C3EBB4A1689E0
2 changed files with 10 additions and 3 deletions
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11
llvm/lib/Transforms/Utils/SimplifyCFG.cpp
View File

@ -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;
}

2
llvm/test/Transforms/SimplifyCFG/duplicate-landingpad.ll
View File

@ -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"
declare i32 @__gxx_personality_v0(...)