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https://github.com/capstone-engine/llvm-capstone.git
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[Attributor] Simplify switches with more than one potential condition
Before, we allowed the condition to be simplified to a simple constant only, otherwise we assumed all successors are live. Now we allow multiple constants, and mark the default successor as dead accordingly.
This commit is contained in:
Johannes Doerfert
parent
a9167c2e47
commit
361b536bbc
@ -4776,23 +4776,53 @@ identifyAliveSuccessors(Attributor &A, const SwitchInst &SI,
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AbstractAttribute &AA,
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SmallVectorImpl<const Instruction *> &AliveSuccessors) {
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bool UsedAssumedInformation = false;
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std::optional<Constant *> C =
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A.getAssumedConstant(*SI.getCondition(), AA, UsedAssumedInformation);
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if (!C || isa_and_nonnull<UndefValue>(*C)) {
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// No value yet, assume all edges are dead.
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} else if (isa_and_nonnull<ConstantInt>(*C)) {
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for (const auto &CaseIt : SI.cases()) {
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if (CaseIt.getCaseValue() == *C) {
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AliveSuccessors.push_back(&CaseIt.getCaseSuccessor()->front());
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return UsedAssumedInformation;
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}
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}
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AliveSuccessors.push_back(&SI.getDefaultDest()->front());
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return UsedAssumedInformation;
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} else {
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SmallVector<AA::ValueAndContext> Values;
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if (!A.getAssumedSimplifiedValues(IRPosition::value(*SI.getCondition()), &AA,
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Values, AA::AnyScope,
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UsedAssumedInformation)) {
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// Something went wrong, assume all successors are live.
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for (const BasicBlock *SuccBB : successors(SI.getParent()))
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AliveSuccessors.push_back(&SuccBB->front());
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return false;
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}
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if (Values.empty() ||
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(Values.size() == 1 &&
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isa_and_nonnull<UndefValue>(Values.front().getValue()))) {
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// No valid value yet, assume all edges are dead.
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return UsedAssumedInformation;
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}
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Type &Ty = *SI.getCondition()->getType();
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SmallPtrSet<ConstantInt *, 8> Constants;
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auto CheckForConstantInt = [&](Value *V) {
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if (auto *CI = dyn_cast_if_present<ConstantInt>(AA::getWithType(*V, Ty))) {
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Constants.insert(CI);
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return true;
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}
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return false;
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};
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if (!all_of(Values, [&](AA::ValueAndContext &VAC) {
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return CheckForConstantInt(VAC.getValue());
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})) {
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for (const BasicBlock *SuccBB : successors(SI.getParent()))
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AliveSuccessors.push_back(&SuccBB->front());
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return UsedAssumedInformation;
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}
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unsigned MatchedCases = 0;
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for (const auto &CaseIt : SI.cases()) {
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if (Constants.count(CaseIt.getCaseValue())) {
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++MatchedCases;
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AliveSuccessors.push_back(&CaseIt.getCaseSuccessor()->front());
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}
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}
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// If all potential values have been matched, we will not visit the default
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// case.
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if (MatchedCases < Constants.size())
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AliveSuccessors.push_back(&SI.getDefaultDest()->front());
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return UsedAssumedInformation;
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}
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@ -1505,6 +1505,134 @@ define i1 @constexpr_icmp2() {
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ret i1 icmp eq (ptr addrspacecast (ptr addrspace(4) @str to ptr), ptr null)
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}
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define i8 @switch(i1 %c1, i1 %c2) {
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; TUNIT: Function Attrs: mustprogress nofree norecurse nosync nounwind willreturn memory(none)
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; TUNIT-LABEL: define {{[^@]+}}@switch
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; TUNIT-SAME: (i1 noundef [[C1:%.*]], i1 [[C2:%.*]]) #[[ATTR2]] {
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; TUNIT-NEXT: entry:
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; TUNIT-NEXT: br i1 [[C1]], label [[T:%.*]], label [[F:%.*]]
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; TUNIT: t:
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; TUNIT-NEXT: br label [[M:%.*]]
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; TUNIT: f:
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; TUNIT-NEXT: br label [[M]]
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; TUNIT: m:
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; TUNIT-NEXT: [[J:%.*]] = phi i32 [ 0, [[T]] ], [ 4, [[F]] ]
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; TUNIT-NEXT: switch i32 [[J]], label [[DEFAULT1:%.*]] [
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; TUNIT-NEXT: i32 1, label [[DEAD1:%.*]]
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; TUNIT-NEXT: i32 2, label [[DEAD2:%.*]]
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; TUNIT-NEXT: i32 3, label [[DEAD3:%.*]]
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; TUNIT-NEXT: i32 4, label [[ALIVE1:%.*]]
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; TUNIT-NEXT: ]
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; TUNIT: default1:
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; TUNIT-NEXT: br label [[ALIVE1]]
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; TUNIT: alive1:
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; TUNIT-NEXT: [[K:%.*]] = phi i32 [ 1, [[M]] ], [ 4, [[DEFAULT1]] ]
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; TUNIT-NEXT: switch i32 [[K]], label [[DEAD4:%.*]] [
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; TUNIT-NEXT: i32 1, label [[END1:%.*]]
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; TUNIT-NEXT: i32 2, label [[DEAD5:%.*]]
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; TUNIT-NEXT: i32 4, label [[END2:%.*]]
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; TUNIT-NEXT: ]
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; TUNIT: end1:
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; TUNIT-NEXT: ret i8 -1
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; TUNIT: end2:
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; TUNIT-NEXT: ret i8 -2
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; TUNIT: dead1:
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; TUNIT-NEXT: unreachable
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; TUNIT: dead2:
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; TUNIT-NEXT: unreachable
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; TUNIT: dead3:
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; TUNIT-NEXT: unreachable
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; TUNIT: dead4:
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; TUNIT-NEXT: unreachable
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; TUNIT: dead5:
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; TUNIT-NEXT: unreachable
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;
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; CGSCC: Function Attrs: mustprogress nofree norecurse nosync nounwind willreturn memory(none)
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; CGSCC-LABEL: define {{[^@]+}}@switch
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; CGSCC-SAME: (i1 noundef [[C1:%.*]], i1 [[C2:%.*]]) #[[ATTR1]] {
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; CGSCC-NEXT: entry:
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; CGSCC-NEXT: br i1 [[C1]], label [[T:%.*]], label [[F:%.*]]
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; CGSCC: t:
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; CGSCC-NEXT: br label [[M:%.*]]
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; CGSCC: f:
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; CGSCC-NEXT: br label [[M]]
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; CGSCC: m:
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; CGSCC-NEXT: [[J:%.*]] = phi i32 [ 0, [[T]] ], [ 4, [[F]] ]
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; CGSCC-NEXT: switch i32 [[J]], label [[DEFAULT1:%.*]] [
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; CGSCC-NEXT: i32 1, label [[DEAD1:%.*]]
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; CGSCC-NEXT: i32 2, label [[DEAD2:%.*]]
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; CGSCC-NEXT: i32 3, label [[DEAD3:%.*]]
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; CGSCC-NEXT: i32 4, label [[ALIVE1:%.*]]
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; CGSCC-NEXT: ]
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; CGSCC: default1:
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; CGSCC-NEXT: br label [[ALIVE1]]
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; CGSCC: alive1:
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; CGSCC-NEXT: [[K:%.*]] = phi i32 [ 1, [[M]] ], [ 4, [[DEFAULT1]] ]
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; CGSCC-NEXT: switch i32 [[K]], label [[DEAD4:%.*]] [
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; CGSCC-NEXT: i32 1, label [[END1:%.*]]
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; CGSCC-NEXT: i32 2, label [[DEAD5:%.*]]
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; CGSCC-NEXT: i32 4, label [[END2:%.*]]
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; CGSCC-NEXT: ]
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; CGSCC: end1:
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; CGSCC-NEXT: ret i8 -1
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; CGSCC: end2:
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; CGSCC-NEXT: ret i8 -2
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; CGSCC: dead1:
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; CGSCC-NEXT: unreachable
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; CGSCC: dead2:
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; CGSCC-NEXT: unreachable
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; CGSCC: dead3:
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; CGSCC-NEXT: unreachable
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; CGSCC: dead4:
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; CGSCC-NEXT: unreachable
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; CGSCC: dead5:
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; CGSCC-NEXT: unreachable
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;
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entry:
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br i1 %c1, label %t, label %f
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t:
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br label %m
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f:
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br label %m
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m:
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%j = phi i32 [ 0, %t ], [ 4, %f ]
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switch i32 %j, label %default1 [
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i32 1, label %dead1
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i32 2, label %dead2
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i32 3, label %dead3
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i32 4, label %alive1
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]
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default1:
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br label %alive1
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alive1:
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%k = phi i32 [ 1, %m ], [ 4, %default1 ]
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switch i32 %k, label %dead4 [
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i32 1, label %end1
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i32 2, label %dead5
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i32 4, label %end2
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]
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end1:
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ret i8 -1
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end2:
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ret i8 -2
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dead1:
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ret i8 1
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dead2:
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ret i8 2
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dead3:
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ret i8 3
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dead4:
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ret i8 4
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dead5:
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ret i8 5
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}
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;.
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; TUNIT: attributes #[[ATTR0:[0-9]+]] = { nocallback nofree nosync nounwind willreturn }
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; TUNIT: attributes #[[ATTR1]] = { memory(readwrite, argmem: none) }
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