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[NFCI][SimplifyCFG] Rewrite `createUnreachableSwitchDefault()` 

The only thing that function should do as per it's semantic,
is to ensure that the switch's default is a block consisting only of
an `unreachable` terminator.

So let's just create such a block and update switch's default
to point to it. There should be no need for all this weird dance
around predecessors/successors.
This commit is contained in:
Roman Lebedev 2021-08-20 13:17:56 +03:00
parent 94c4952951
commit 5d4f37e895
No known key found for this signature in database
GPG Key ID: 083C3EBB4A1689E0
2 changed files with 13 additions and 16 deletions
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25
llvm/lib/Transforms/Utils/SimplifyCFG.cpp
View File

@ -4747,23 +4747,20 @@ static void createUnreachableSwitchDefault(SwitchInst *Switch,
DomTreeUpdater *DTU) {
LLVM_DEBUG(dbgs() << "SimplifyCFG: switch default is dead.\n");
auto *BB = Switch->getParent();
BasicBlock *NewDefaultBlock = SplitBlockPredecessors(
Switch->getDefaultDest(), Switch->getParent(), "", DTU);
auto *OrigDefaultBlock = Switch->getDefaultDest();
OrigDefaultBlock->removePredecessor(BB);
BasicBlock *NewDefaultBlock = BasicBlock::Create(
BB->getContext(), BB->getName() + ".unreachabledefault", BB->getParent(),
OrigDefaultBlock);
new UnreachableInst(Switch->getContext(), NewDefaultBlock);
Switch->setDefaultDest(&*NewDefaultBlock);
if (DTU)
DTU->applyUpdates({{DominatorTree::Insert, BB, &*NewDefaultBlock},
{DominatorTree::Delete, BB, OrigDefaultBlock}});
SplitBlock(&*NewDefaultBlock, &NewDefaultBlock->front(), DTU);
SmallVector<DominatorTree::UpdateType, 2> Updates;
if (DTU)
for (auto *Successor : successors(NewDefaultBlock))
Updates.push_back({DominatorTree::Delete, NewDefaultBlock, Successor});
auto *NewTerminator = NewDefaultBlock->getTerminator();
new UnreachableInst(Switch->getContext(), NewTerminator);
EraseTerminatorAndDCECond(NewTerminator);
if (DTU)
if (DTU) {
SmallVector<DominatorTree::UpdateType, 2> Updates;
Updates.push_back({DominatorTree::Insert, BB, &*NewDefaultBlock});
if (!is_contained(successors(BB), OrigDefaultBlock))
Updates.push_back({DominatorTree::Delete, BB, &*OrigDefaultBlock});
DTU->applyUpdates(Updates);
}
}
/// Turn a switch with two reachable destinations into an integer range

4
llvm/test/Transforms/SimplifyCFG/switch-dead-default.ll
View File

@ -33,7 +33,7 @@ default:
define void @test2(i2 %a) {
; CHECK-LABEL: @test2(
; CHECK-NEXT: switch i2 [[A:%.*]], label [[DEFAULT1:%.*]] [
; CHECK-NEXT: switch i2 [[A:%.*]], label [[DOTUNREACHABLEDEFAULT:%.*]] [
; CHECK-NEXT: i2 0, label [[CASE0:%.*]]
; CHECK-NEXT: i2 1, label [[CASE1:%.*]]
; CHECK-NEXT: i2 -2, label [[CASE2:%.*]]
@ -53,7 +53,7 @@ define void @test2(i2 %a) {
; CHECK: case3:
; CHECK-NEXT: call void @foo(i32 3)
; CHECK-NEXT: br label [[COMMON_RET]]
; CHECK: default1:
; CHECK: .unreachabledefault:
; CHECK-NEXT: unreachable
;
switch i2 %a, label %default [i2 0, label %case0