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Revert r332657: "[AA] cfl-anders-aa with field sensitivity" 

I don't believe the person who LGTMed this review has appropriate
context on this code. I apologize if I'm wrong.

llvm-svn: 332674
This commit is contained in:
George Burgess IV 2018-05-17 21:56:39 +00:00
parent 860d460063
commit c6526176cf
4 changed files with 109 additions and 257 deletions
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19
llvm/lib/Analysis/AliasAnalysisSummary.h
View File

@ -134,31 +134,18 @@ inline bool operator>=(InterfaceValue LHS, InterfaceValue RHS) {
return !(LHS < RHS);
}
using FieldOffset = int64_t;
// We use UnknownOffset to represent pointer offsets that cannot be determined
// at compile time. Note that MemoryLocation::UnknownSize cannot be used here
// because we require a signed value.
static const FieldOffset UnknownOffset =
std::numeric_limits<FieldOffset>::max();
static const int64_t UnknownOffset = INT64_MAX;
inline FieldOffset addFieldOffset(FieldOffset LHS, FieldOffset RHS) {
inline int64_t addOffset(int64_t LHS, int64_t RHS) {
if (LHS == UnknownOffset || RHS == UnknownOffset)
return UnknownOffset;
// FIXME: Do we need to guard against integer overflow here?
return LHS + RHS;
}
inline FieldOffset subFieldOffset(FieldOffset LHS, FieldOffset RHS) {
if (LHS == UnknownOffset || RHS == UnknownOffset)
return UnknownOffset;
return LHS - RHS;
}
inline FieldOffset negFieldOffset(FieldOffset Offset) {
return subFieldOffset(0, Offset);
}
/// We use ExternalRelation to describe an externally visible aliasing relations
/// between parameters/return value of a function.
struct ExternalRelation {

235
llvm/lib/Analysis/CFLAndersAliasAnalysis.cpp
View File

@ -153,59 +153,11 @@ struct OffsetInstantiatedValue {
bool operator==(OffsetInstantiatedValue LHS, OffsetInstantiatedValue RHS) {
return LHS.IVal == RHS.IVal && LHS.Offset == RHS.Offset;
}
}
namespace llvm {
// Specialize DenseMapInfo for OffsetValue.
template <> struct DenseMapInfo<OffsetValue> {
static OffsetValue getEmptyKey() {
return OffsetValue{DenseMapInfo<const Value *>::getEmptyKey(),
DenseMapInfo<FieldOffset>::getEmptyKey()};
}
static OffsetValue getTombstoneKey() {
return OffsetValue{DenseMapInfo<const Value *>::getTombstoneKey(),
DenseMapInfo<FieldOffset>::getEmptyKey()};
}
static unsigned getHashValue(const OffsetValue &OVal) {
return DenseMapInfo<std::pair<const Value *, FieldOffset>>::getHashValue(
std::make_pair(OVal.Val, OVal.Offset));
}
static bool isEqual(const OffsetValue &LHS, const OffsetValue &RHS) {
return LHS == RHS;
}
};
// Specialize DenseMapInfo for OffsetInstantiatedValue.
template <> struct DenseMapInfo<OffsetInstantiatedValue> {
static OffsetInstantiatedValue getEmptyKey() {
return OffsetInstantiatedValue{
DenseMapInfo<InstantiatedValue>::getEmptyKey(),
DenseMapInfo<FieldOffset>::getEmptyKey()};
}
static OffsetInstantiatedValue getTombstoneKey() {
return OffsetInstantiatedValue{
DenseMapInfo<InstantiatedValue>::getTombstoneKey(),
DenseMapInfo<FieldOffset>::getEmptyKey()};
}
static unsigned getHashValue(const OffsetInstantiatedValue &OVal) {
return DenseMapInfo<std::pair<InstantiatedValue, FieldOffset>>::
getHashValue(std::make_pair(OVal.IVal, OVal.Offset));
}
static bool isEqual(const OffsetInstantiatedValue &LHS,
const OffsetInstantiatedValue &RHS) {
return LHS == RHS;
}
};
} // namespace llvm
namespace {
// We use ReachabilitySet to keep track of value aliases (The nonterminal "V" in
// the paper) during the analysis.
class ReachabilitySet {
using ValueStateMap = DenseMap<OffsetInstantiatedValue, StateSet>;
using ValueStateMap = DenseMap<InstantiatedValue, StateSet>;
using ValueReachMap = DenseMap<InstantiatedValue, ValueStateMap>;
ValueReachMap ReachMap;
@ -214,11 +166,10 @@ public:
using const_valuestate_iterator = ValueStateMap::const_iterator;
using const_value_iterator = ValueReachMap::const_iterator;
// Insert edge 'From->To' at state 'State' with offset 'Offset'
bool insert(InstantiatedValue From, InstantiatedValue To, FieldOffset Offset,
MatchState State) {
// Insert edge 'From->To' at state 'State'
bool insert(InstantiatedValue From, InstantiatedValue To, MatchState State) {
assert(From != To);
auto &States = ReachMap[To][OffsetInstantiatedValue{From, Offset}];
auto &States = ReachMap[To][From];
auto Idx = static_cast<size_t>(State);
if (!States.test(Idx)) {
States.set(Idx);
@ -303,7 +254,6 @@ public:
struct WorkListItem {
InstantiatedValue From;
InstantiatedValue To;
FieldOffset Offset;
MatchState State;
};
@ -311,13 +261,63 @@ struct ValueSummary {
struct Record {
InterfaceValue IValue;
unsigned DerefLevel;
FieldOffset Offset;
};
SmallVector<Record, 4> FromRecords, ToRecords;
};
} // end anonymous namespace
namespace llvm {
// Specialize DenseMapInfo for OffsetValue.
template <> struct DenseMapInfo<OffsetValue> {
static OffsetValue getEmptyKey() {
return OffsetValue{DenseMapInfo<const Value *>::getEmptyKey(),
DenseMapInfo<int64_t>::getEmptyKey()};
}
static OffsetValue getTombstoneKey() {
return OffsetValue{DenseMapInfo<const Value *>::getTombstoneKey(),
DenseMapInfo<int64_t>::getEmptyKey()};
}
static unsigned getHashValue(const OffsetValue &OVal) {
return DenseMapInfo<std::pair<const Value *, int64_t>>::getHashValue(
std::make_pair(OVal.Val, OVal.Offset));
}
static bool isEqual(const OffsetValue &LHS, const OffsetValue &RHS) {
return LHS == RHS;
}
};
// Specialize DenseMapInfo for OffsetInstantiatedValue.
template <> struct DenseMapInfo<OffsetInstantiatedValue> {
static OffsetInstantiatedValue getEmptyKey() {
return OffsetInstantiatedValue{
DenseMapInfo<InstantiatedValue>::getEmptyKey(),
DenseMapInfo<int64_t>::getEmptyKey()};
}
static OffsetInstantiatedValue getTombstoneKey() {
return OffsetInstantiatedValue{
DenseMapInfo<InstantiatedValue>::getTombstoneKey(),
DenseMapInfo<int64_t>::getEmptyKey()};
}
static unsigned getHashValue(const OffsetInstantiatedValue &OVal) {
return DenseMapInfo<std::pair<InstantiatedValue, int64_t>>::getHashValue(
std::make_pair(OVal.IVal, OVal.Offset));
}
static bool isEqual(const OffsetInstantiatedValue &LHS,
const OffsetInstantiatedValue &RHS) {
return LHS == RHS;
}
};
} // end namespace llvm
class CFLAndersAAResult::FunctionInfo {
/// Map a value to other values that may alias it
/// Since the alias relation is symmetric, to save some space we assume values
@ -389,11 +389,9 @@ populateAliasMap(DenseMap<const Value *, std::vector<OffsetValue>> &AliasMap,
auto Val = OuterMapping.first.Val;
auto &AliasList = AliasMap[Val];
for (const auto &InnerMapping : OuterMapping.second) {
auto OVal = InnerMapping.first;
// Again, AliasMap only cares about top-level values
if (OVal.IVal.DerefLevel == 0)
AliasList.push_back(
OffsetValue{OVal.IVal.Val, negFieldOffset(OVal.Offset)});
if (InnerMapping.first.DerefLevel == 0)
AliasList.push_back(OffsetValue{InnerMapping.first.Val, UnknownOffset});
}
// Sort AliasList for faster lookup
@ -432,27 +430,24 @@ static void populateExternalRelations(
for (const auto &OuterMapping : ReachSet.value_mappings()) {
if (auto Dst = getInterfaceValue(OuterMapping.first, RetVals)) {
for (const auto &InnerMapping : OuterMapping.second) {
auto OVal = InnerMapping.first;
auto SrcIVal = OVal.IVal;
auto Offset = OVal.Offset;
// If Src is a param/return value, we get a same-level assignment.
if (auto Src = getInterfaceValue(SrcIVal, RetVals)) {
if (auto Src = getInterfaceValue(InnerMapping.first, RetVals)) {
// This may happen if both Dst and Src are return values
if (*Dst == *Src)
continue;
if (hasReadOnlyState(InnerMapping.second))
ExtRelations.push_back(ExternalRelation{*Dst, *Src, Offset});
ExtRelations.push_back(ExternalRelation{*Dst, *Src, UnknownOffset});
// No need to check for WriteOnly state, since ReachSet is symmetric
} else {
// If Src is not a param/return, add it to ValueMap
auto SrcIVal = InnerMapping.first;
if (hasReadOnlyState(InnerMapping.second))
ValueMap[SrcIVal.Val].FromRecords.push_back(
ValueSummary::Record{*Dst, SrcIVal.DerefLevel, Offset});
ValueSummary::Record{*Dst, SrcIVal.DerefLevel});
if (hasWriteOnlyState(InnerMapping.second))
ValueMap[SrcIVal.Val].ToRecords.push_back(
ValueSummary::Record{*Dst, SrcIVal.DerefLevel, Offset});
ValueSummary::Record{*Dst, SrcIVal.DerefLevel});
}
}
}
@ -471,20 +466,14 @@ static void populateExternalRelations(
auto SrcLevel = FromRecord.IValue.DerefLevel;
auto DstIndex = ToRecord.IValue.Index;
auto DstLevel = ToRecord.IValue.DerefLevel;
// Offsets to be pushed to External Relations
auto SrcOffset = FromRecord.Offset;
auto DstOffset = ToRecord.Offset;
if (ToLevel > FromLevel)
SrcLevel += ToLevel - FromLevel;
else
DstLevel += FromLevel - ToLevel;
ExtRelations.push_back(
ExternalRelation{InterfaceValue{SrcIndex, SrcLevel},
InterfaceValue{DstIndex, DstLevel},
subFieldOffset(SrcOffset, DstOffset)});
ExtRelations.push_back(ExternalRelation{
InterfaceValue{SrcIndex, SrcLevel},
InterfaceValue{DstIndex, DstLevel}, UnknownOffset});
}
}
}
@ -602,14 +591,12 @@ bool CFLAndersAAResult::FunctionInfo::mayAlias(const Value *LHS,
}
static void propagate(InstantiatedValue From, InstantiatedValue To,
FieldOffset Offset, MatchState State,
ReachabilitySet &ReachSet,
MatchState State, ReachabilitySet &ReachSet,
std::vector<WorkListItem> &WorkList) {
if (From == To)
return;
if (ReachSet.insert(From, To, Offset, State))
WorkList.push_back(WorkListItem{From, To, Offset, State});
if (ReachSet.insert(From, To, State))
WorkList.push_back(WorkListItem{From, To, State});
}
static void initializeWorkList(std::vector<WorkListItem> &WorkList,
@ -623,15 +610,13 @@ static void initializeWorkList(std::vector<WorkListItem> &WorkList,
// Insert all immediate assignment neighbors to the worklist
for (unsigned I = 0, E = ValueInfo.getNumLevels(); I < E; ++I) {
auto Src = InstantiatedValue{Val, I};
// If we have an assignment edge from X + Offset to Y, it means that
// (Y - Offset) is reachable from X at the state FlowToWriteOnly
// At the same time, (X + Offset) is reachable from Y at the state
// FlowFromReadOnly
// If there's an assignment edge from X to Y, it means Y is reachable from
// X at S2 and X is reachable from Y at S1
for (auto &Edge : ValueInfo.getNodeInfoAtLevel(I).Edges) {
propagate(Edge.Other, Src, Edge.Offset, MatchState::FlowFromReadOnly,
ReachSet, WorkList);
propagate(Src, Edge.Other, negFieldOffset(Edge.Offset),
MatchState::FlowToWriteOnly, ReachSet, WorkList);
propagate(Edge.Other, Src, MatchState::FlowFromReadOnly, ReachSet,
WorkList);
propagate(Src, Edge.Other, MatchState::FlowToWriteOnly, ReachSet,
WorkList);
}
}
}
@ -650,41 +635,37 @@ static void processWorkListItem(const WorkListItem &Item, const CFLGraph &Graph,
std::vector<WorkListItem> &WorkList) {
auto FromNode = Item.From;
auto ToNode = Item.To;
auto Offset = Item.Offset;
auto NodeInfo = Graph.getNode(ToNode);
assert(NodeInfo != nullptr);
// TODO: propagate field offsets
// FIXME: Here is a neat trick we can do: since both ReachSet and MemSet holds
// relations that are symmetric, we could actually cut the storage by half by
// sorting FromNode and ToNode before insertion happens.
// The newly added value alias pair may potentially generate more memory
// alias pairs. Check for them here.
// MemAlias reachability can only be triggered when Offset is 0 or Unknown
if (Offset == 0 || Offset == UnknownOffset) {
auto FromNodeBelow = getNodeBelow(Graph, FromNode);
auto ToNodeBelow = getNodeBelow(Graph, ToNode);
if (FromNodeBelow && ToNodeBelow &&
MemSet.insert(*FromNodeBelow, *ToNodeBelow)) {
propagate(*FromNodeBelow, *ToNodeBelow, Offset,
MatchState::FlowFromMemAliasNoReadWrite, ReachSet, WorkList);
for (const auto &Mapping :
ReachSet.reachableValueAliases(*FromNodeBelow)) {
auto SrcOVal = Mapping.first;
auto MemAliasPropagate = [&](MatchState FromState, MatchState ToState) {
if (Mapping.second.test(static_cast<size_t>(FromState)))
propagate(SrcOVal.IVal, *ToNodeBelow, SrcOVal.Offset, ToState,
ReachSet, WorkList);
};
auto FromNodeBelow = getNodeBelow(Graph, FromNode);
auto ToNodeBelow = getNodeBelow(Graph, ToNode);
if (FromNodeBelow && ToNodeBelow &&
MemSet.insert(*FromNodeBelow, *ToNodeBelow)) {
propagate(*FromNodeBelow, *ToNodeBelow,
MatchState::FlowFromMemAliasNoReadWrite, ReachSet, WorkList);
for (const auto &Mapping : ReachSet.reachableValueAliases(*FromNodeBelow)) {
auto Src = Mapping.first;
auto MemAliasPropagate = [&](MatchState FromState, MatchState ToState) {
if (Mapping.second.test(static_cast<size_t>(FromState)))
propagate(Src, *ToNodeBelow, ToState, ReachSet, WorkList);
};
MemAliasPropagate(MatchState::FlowFromReadOnly,
MatchState::FlowFromMemAliasReadOnly);
MemAliasPropagate(MatchState::FlowToWriteOnly,
MatchState::FlowToMemAliasWriteOnly);
MemAliasPropagate(MatchState::FlowToReadWrite,
MatchState::FlowToMemAliasReadWrite);
}
MemAliasPropagate(MatchState::FlowFromReadOnly,
MatchState::FlowFromMemAliasReadOnly);
MemAliasPropagate(MatchState::FlowToWriteOnly,
MatchState::FlowToMemAliasWriteOnly);
MemAliasPropagate(MatchState::FlowToReadWrite,
MatchState::FlowToMemAliasReadWrite);
}
}
@ -697,23 +678,17 @@ static void processWorkListItem(const WorkListItem &Item, const CFLGraph &Graph,
// - If Y is an alias of X, then reverse assignment edges (if there is any)
// should precede any assignment edges on the path from X to Y.
auto NextAssignState = [&](MatchState State) {
for (const auto &AssignEdge : NodeInfo->Edges) {
propagate(FromNode, AssignEdge.Other,
subFieldOffset(Offset, AssignEdge.Offset), State, ReachSet,
WorkList);
}
for (const auto &AssignEdge : NodeInfo->Edges)
propagate(FromNode, AssignEdge.Other, State, ReachSet, WorkList);
};
auto NextRevAssignState = [&](MatchState State) {
for (const auto &RevAssignEdge : NodeInfo->ReverseEdges) {
propagate(FromNode, RevAssignEdge.Other,
addFieldOffset(Offset, RevAssignEdge.Offset), State, ReachSet,
WorkList);
}
for (const auto &RevAssignEdge : NodeInfo->ReverseEdges)
propagate(FromNode, RevAssignEdge.Other, State, ReachSet, WorkList);
};
auto NextMemState = [&](MatchState State) {
if (auto AliasSet = MemSet.getMemoryAliases(ToNode)) {
for (const auto &MemAlias : *AliasSet)
propagate(FromNode, MemAlias, Offset, State, ReachSet, WorkList);
propagate(FromNode, MemAlias, State, ReachSet, WorkList);
}
};
@ -778,7 +753,7 @@ static AliasAttrMap buildAttrMap(const CFLGraph &Graph,
// Propagate attr on the same level
for (const auto &Mapping : ReachSet.reachableValueAliases(Dst)) {
auto Src = Mapping.first.IVal;
auto Src = Mapping.first;
if (AttrMap.add(Src, DstAttr))
NextList.push_back(Src);
}
@ -813,19 +788,11 @@ CFLAndersAAResult::buildInfoFrom(const Function &Fn) {
std::vector<WorkListItem> WorkList, NextList;
initializeWorkList(WorkList, ReachSet, Graph);
bool LoopInGraph = false;
// TODO: make sure we don't stop before the fix point is reached
while (!WorkList.empty()) {
for (const auto &Item : WorkList)
processWorkListItem(Item, Graph, ReachSet, MemSet, NextList);
if (NextList.size() == WorkList.size()) {
// stop if loop in CFL graph
if (LoopInGraph)
break;
LoopInGraph = true;
}
NextList.swap(WorkList);
NextList.clear();
}

10
llvm/lib/Analysis/CFLGraph.h
View File

@ -62,7 +62,7 @@ public:
struct Edge {
Node Other;
FieldOffset Offset;
int64_t Offset;
};
using EdgeList = std::vector<Edge>;
@ -125,7 +125,7 @@ public:
Info->Attr |= Attr;
}
void addEdge(Node From, Node To, FieldOffset Offset = 0) {
void addEdge(Node From, Node To, int64_t Offset = 0) {
auto *FromInfo = getNode(From);
assert(FromInfo != nullptr);
auto *ToInfo = getNode(To);
@ -219,7 +219,7 @@ template <typename CFLAA> class CFLGraphBuilder {
Graph.addNode(InstantiatedValue{Val, 0}, Attr);
}
void addAssignEdge(Value *From, Value *To, FieldOffset Offset = 0) {
void addAssignEdge(Value *From, Value *To, int64_t Offset = 0) {
assert(From != nullptr && To != nullptr);
if (!From->getType()->isPointerTy() || !To->getType()->isPointerTy())
return;
@ -312,7 +312,7 @@ template <typename CFLAA> class CFLGraphBuilder {
}
void visitGEP(GEPOperator &GEPOp) {
FieldOffset Offset = UnknownOffset;
uint64_t Offset = UnknownOffset;
APInt APOffset(DL.getPointerSizeInBits(GEPOp.getPointerAddressSpace()),
0);
if (GEPOp.accumulateConstantOffset(DL, APOffset))
@ -397,7 +397,7 @@ template <typename CFLAA> class CFLGraphBuilder {
if (IRelation.hasValue()) {
Graph.addNode(IRelation->From);
Graph.addNode(IRelation->To);
Graph.addEdge(IRelation->From, IRelation->To, IRelation->Offset);
Graph.addEdge(IRelation->From, IRelation->To);
}
}

102
llvm/test/Analysis/CFLAliasAnalysis/Andersen/field.ll
View File

@ -1,102 +0,0 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
; RUN: opt < %s -disable-basicaa -cfl-anders-aa -aa-eval -print-all-alias-modref-info -disable-output 2>&1 | FileCheck %s
; RUN: opt < %s -aa-pipeline=cfl-anders-aa -passes=aa-eval -print-all-alias-modref-info -disable-output 2>&1 | FileCheck %s
; CHECK: Function: test_simple_offsets
; CHECK: NoAlias: i64* %b, i64** %acast
; CHECK: NoAlias: i64** %acast, i64** %aoff
; CHECK: NoAlias: i64* %b, i64** %acastoff
; CHECK: NoAlias: i64** %acast, i64** %acastoff
; CHECK: NoAlias: [2 x i64*]* %a, i64* %acastload
; CHECK: MayAlias: i64* %acastload, i64* %b
; CHECK: NoAlias: i64* %acastload, i64** %aoff
; CHECK: NoAlias: i64* %acastload, i64** %acast
; CHECK: NoAlias: i64* %acastload, i64** %acastoff
define void @test_simple_offsets() {
%a = alloca [2 x i64*], align 8
%b = alloca i64, align 4
%aoff = getelementptr inbounds [2 x i64*], [2 x i64*]* %a, i64 0, i64 1
store i64* %b, i64** %aoff
%acast = bitcast [2 x i64*]* %a to i64**
%acastoff = getelementptr inbounds i64*, i64** %acast, i64 1
%acastload = load i64*, i64** %acastoff
ret void
}
; CHECK: Function: test_unknown_offset
; CHECK: MayAlias: [3 x i32]* %a, i32* %an
; CHECK: MayAlias: i32* %a4, i32* %an
; CHECK: MayAlias: i32* %a8, i32* %an
; CHECK: MayAlias: i32* %an, i32* %b
; CHECK: MayAlias: [3 x i32]* %a, i32* %bn
; CHECK: MayAlias: i32* %a4, i32* %bn
; CHECK: MayAlias: i32* %a8, i32* %bn
; CHECK: MayAlias: i32* %an, i32* %bn
; CHECK: MayAlias: i32* %b, i32* %bn
define void @test_unknown_offset(i32 %n) {
%a = alloca [3 x i32], align 4
%a4 = getelementptr inbounds [3 x i32], [3 x i32]* %a, i32 0, i32 1
%a8 = getelementptr inbounds [3 x i32], [3 x i32]* %a, i32 0, i32 2
%an = getelementptr inbounds [3 x i32], [3 x i32]* %a, i32 0, i32 %n
%b = bitcast [3 x i32]* %a to i32*
%bn = getelementptr inbounds i32, i32* %b, i32 %n
ret void
}
%S = type { i32, i32, i32 }
define i32* @return_arg(%S* %arg1, %S* %arg2) {
%acast = bitcast %S* %arg1 to i32*
%aoffset = getelementptr i32, i32* %acast, i32 1
ret i32* %aoffset
}
define i32* @return_derefence_arg(%S** %arg1) {
%deref = load %S*, %S** %arg1
%deref2 = getelementptr %S, %S* %deref, i32 0, i32 1
ret i32* %deref2
}
; CHECK-LABEL: Function: test_return_arg_offset
; CHECK: NoAlias: %S* %a, %S* %b
; CHECK: MayAlias: %S* %a, i32* %c
; CHECK: NoAlias: %S* %b, i32* %c
; CHECK: NoAlias: i32* %acast, i32* %c
; CHECK: NoAlias: i32* %acast, i32* %d
define void @test_return_arg_offset() {
%a = alloca %S, align 8
%b = alloca %S, align 8
%c = call i32* @return_arg(%S* %a, %S* %b)
%d = getelementptr %S, %S* %a, i32 0, i32 1
%acast = bitcast %S* %a to i32*
ret void
}
; CHECK-LABEL: Function: test_return_derefence_arg
; CHECK: NoAlias: %S** %p, i32* %c
; CHECK: NoAlias: %S* %lp, %S** %p
; CHECK: MayAlias: %S* %lp, i32* %c
; CHECK: NoAlias: %S** %p, i32* %lp_off
; CHECK: MayAlias: i32* %c, i32* %lp_off
; CHECK: MayAlias: %S* %lp, i32* %lp_off
; CHECK: NoAlias: %S** %p, i32* %acast
; CHECK: NoAlias: i32* %acast, i32* %c
; CHECK: MayAlias: %S* %lp, i32* %acast
; CHECK: NoAlias: i32* %acast, i32* %lp_off
define void @test_return_derefence_arg() {
%a = alloca %S, align 8
%p = alloca %S*, align 8
store %S* %a, %S** %p
%c = call i32* @return_derefence_arg(%S** %p)
%lp = load %S*, %S** %p
%lp_off = getelementptr %S, %S* %lp, i32 0, i32 1
%acast = bitcast %S* %a to i32*
ret void
}