forked from OSchip/llvm-project
[IPSCCP] Support unfeasible default dests for switch.
At the moment, unfeasible default destinations are not handled properly in removeNonFeasibleEdges. So far, only unfeasible cases are removed, but later code expects unreachable blocks to have no predecessors. This is causing the crash reported in PR49573. If the default destination is unfeasible it won't be executed. Create a new unreachable block on demand and use that as default destination. Note that at the moment this only is relevant for cases where resolvedUndefsIn marks the first case as executable. Regular switch handling has a FIXME/TODO to support determining whether the default case is feasible or not. Fixes #48917. Differential Revision: https://reviews.llvm.org/D113497
This commit is contained in:
Florian Hahn
parent
5b3ca24a35
commit
857c612d89
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@ -336,7 +336,8 @@ static void findReturnsToZap(Function &F,
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}
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static bool removeNonFeasibleEdges(const SCCPSolver &Solver, BasicBlock *BB,
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DomTreeUpdater &DTU) {
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DomTreeUpdater &DTU,
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BasicBlock *&NewUnreachableBB) {
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SmallPtrSet<BasicBlock *, 8> FeasibleSuccessors;
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bool HasNonFeasibleEdges = false;
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for (BasicBlock *Succ : successors(BB)) {
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@ -379,6 +380,23 @@ static bool removeNonFeasibleEdges(const SCCPSolver &Solver, BasicBlock *BB,
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} else if (FeasibleSuccessors.size() > 1) {
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SwitchInstProfUpdateWrapper SI(*cast<SwitchInst>(TI));
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SmallVector<DominatorTree::UpdateType, 8> Updates;
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// If the default destination is unfeasible it will never be taken. Replace
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// it with a new block with a single Unreachable instruction.
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BasicBlock *DefaultDest = SI->getDefaultDest();
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if (!FeasibleSuccessors.contains(DefaultDest)) {
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if (!NewUnreachableBB) {
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NewUnreachableBB =
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BasicBlock::Create(DefaultDest->getContext(), "default.unreachable",
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DefaultDest->getParent(), DefaultDest);
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new UnreachableInst(DefaultDest->getContext(), NewUnreachableBB);
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}
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SI->setDefaultDest(NewUnreachableBB);
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Updates.push_back({DominatorTree::Delete, BB, DefaultDest});
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Updates.push_back({DominatorTree::Insert, BB, NewUnreachableBB});
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}
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for (auto CI = SI->case_begin(); CI != SI->case_end();) {
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if (FeasibleSuccessors.contains(CI->getCaseSuccessor())) {
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++CI;
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@ -526,8 +544,9 @@ bool llvm::runIPSCCP(
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NumInstRemoved += changeToUnreachable(F.front().getFirstNonPHI(),
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/*PreserveLCSSA=*/false, &DTU);
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BasicBlock *NewUnreachableBB = nullptr;
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for (BasicBlock &BB : F)
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MadeChanges |= removeNonFeasibleEdges(Solver, &BB, DTU);
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MadeChanges |= removeNonFeasibleEdges(Solver, &BB, DTU, NewUnreachableBB);
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for (BasicBlock *DeadBB : BlocksToErase)
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if (!DeadBB->hasAddressTaken())
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@ -1,8 +1,9 @@
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; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
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; RUN: opt -passes=ipsccp < %s -S | FileCheck %s
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; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --function-signature
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; RUN: opt -passes=ipsccp < %s -S | FileCheck --check-prefixes=CHECK,ONCE %s
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; RUN: opt -passes='ipsccp,ipsccp' < %s -S | FileCheck --check-prefixes=CHECK,TWICE %s
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define void @barney() {
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; CHECK-LABEL: @barney(
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; CHECK-LABEL: define {{[^@]+}}@barney() {
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; CHECK-NEXT: bb:
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; CHECK-NEXT: br label [[BB9:%.*]]
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; CHECK: bb6:
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@ -26,7 +27,7 @@ bb9: ; preds = %bb
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}
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define void @blam() {
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; CHECK-LABEL: @blam(
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; CHECK-LABEL: define {{[^@]+}}@blam() {
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; CHECK-NEXT: bb:
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; CHECK-NEXT: br label [[BB16:%.*]]
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; CHECK: bb16:
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@ -59,7 +60,7 @@ bb38: ; preds = %bb16
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define void @hoge() {
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; CHECK-LABEL: @hoge(
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; CHECK-LABEL: define {{[^@]+}}@hoge() {
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; CHECK-NEXT: bb:
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; CHECK-NEXT: br label [[BB2:%.*]]
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; CHECK: bb2:
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@ -89,3 +90,142 @@ bb3: ; preds = %bb2
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bb4: ; preds = %bb2, %bb2, %bb2
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unreachable
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}
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; Test case from PR49573. %default.bb is unfeasible. Make sure it gets replaced
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; by an unreachable block.
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define void @pr49573_main() {
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; ONCE-LABEL: define {{[^@]+}}@pr49573_main() {
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; ONCE-NEXT: entry:
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; ONCE-NEXT: [[TGT:%.*]] = call i16 @pr49573_fn()
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; ONCE-NEXT: switch i16 2, label [[DEFAULT_UNREACHABLE:%.*]] [
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; ONCE-NEXT: i16 0, label [[CASE_0:%.*]]
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; ONCE-NEXT: i16 2, label [[CASE_2:%.*]]
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; ONCE-NEXT: ]
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; ONCE: case.0:
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; ONCE-NEXT: unreachable
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; ONCE: default.unreachable:
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; ONCE-NEXT: unreachable
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; ONCE: case.2:
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; ONCE-NEXT: br label [[NEXT:%.*]]
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; ONCE: next:
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; ONCE-NEXT: [[TGT_2:%.*]] = call i16 @pr49573_fn_2()
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; ONCE-NEXT: switch i16 2, label [[DEFAULT_UNREACHABLE]] [
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; ONCE-NEXT: i16 0, label [[CASE_0]]
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; ONCE-NEXT: i16 2, label [[CASE_2]]
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; ONCE-NEXT: ]
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;
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; TWICE-LABEL: define {{[^@]+}}@pr49573_main() {
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; TWICE-NEXT: entry:
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; TWICE-NEXT: [[TGT:%.*]] = call i16 @pr49573_fn()
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; TWICE-NEXT: br label [[CASE_2:%.*]]
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; TWICE: case.2:
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; TWICE-NEXT: br label [[NEXT:%.*]]
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; TWICE: next:
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; TWICE-NEXT: [[TGT_2:%.*]] = call i16 @pr49573_fn_2()
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; TWICE-NEXT: br label [[CASE_2]]
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;
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entry:
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%tgt = call i16 @pr49573_fn()
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switch i16 %tgt, label %default.bb [
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i16 0, label %case.0
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i16 1, label %case.1
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i16 2, label %case.2
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]
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case.0:
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unreachable
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default.bb:
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ret void
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case.1:
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ret void
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case.2:
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br label %next
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next:
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%tgt.2 = call i16 @pr49573_fn_2()
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switch i16 %tgt.2, label %default.bb [
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i16 0, label %case.0
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i16 2, label %case.2
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]
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}
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; Make sure a new unreachable BB is created.
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define void @pr49573_main_2() {
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; ONCE-LABEL: define {{[^@]+}}@pr49573_main_2() {
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; ONCE-NEXT: entry:
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; ONCE-NEXT: [[TGT:%.*]] = call i16 @pr49573_fn()
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; ONCE-NEXT: switch i16 2, label [[DEFAULT_UNREACHABLE:%.*]] [
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; ONCE-NEXT: i16 0, label [[CASE_0:%.*]]
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; ONCE-NEXT: i16 2, label [[CASE_2:%.*]]
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; ONCE-NEXT: ]
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; ONCE: case.0:
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; ONCE-NEXT: unreachable
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; ONCE: default.unreachable:
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; ONCE-NEXT: unreachable
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; ONCE: case.2:
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; ONCE-NEXT: ret void
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;
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; TWICE-LABEL: define {{[^@]+}}@pr49573_main_2() {
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; TWICE-NEXT: entry:
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; TWICE-NEXT: [[TGT:%.*]] = call i16 @pr49573_fn()
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; TWICE-NEXT: br label [[CASE_2:%.*]]
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; TWICE: case.2:
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; TWICE-NEXT: ret void
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;
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entry:
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%tgt = call i16 @pr49573_fn()
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switch i16 %tgt, label %default.bb [
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i16 0, label %case.0
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i16 1, label %case.1
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i16 2, label %case.2
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]
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case.0:
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unreachable
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default.bb:
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ret void
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case.1:
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ret void
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case.2:
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ret void
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}
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define internal i16 @pr49573_fn() {
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; CHECK-LABEL: define {{[^@]+}}@pr49573_fn() {
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; CHECK-NEXT: entry:
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; CHECK-NEXT: br label [[ELSE:%.*]]
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; CHECK: else:
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; CHECK-NEXT: ret i16 undef
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;
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entry:
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br i1 undef, label %then, label %else
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then:
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ret i16 0
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else:
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ret i16 2
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}
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define internal i16 @pr49573_fn_2() {
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; CHECK-LABEL: define {{[^@]+}}@pr49573_fn_2() {
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; CHECK-NEXT: entry:
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; CHECK-NEXT: br label [[ELSE:%.*]]
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; CHECK: else:
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; CHECK-NEXT: ret i16 undef
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;
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entry:
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br i1 undef, label %then, label %else
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then:
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ret i16 0
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else:
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ret i16 2
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}
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