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[CaptureTracking] Remove dereferenceable_or_null special case #135613

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Merged
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Apr 17, 2025
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[CaptureTracking] Remove dereferenceable_or_null special case #135613

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12 changes: 1 addition & 11 deletions llvm/include/llvm/Analysis/CaptureTracking.h
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Expand Up @@ -156,11 +156,6 @@ namespace llvm {
/// Return one of Stop, Continue or ContinueIgnoringReturn to control
/// further traversal.
virtual Action captured(const Use *U, UseCaptureInfo CI) = 0;

/// isDereferenceableOrNull - Overload to allow clients with additional
/// knowledge about pointer dereferenceability to provide it and thereby
/// avoid conservative responses when a pointer is compared to null.
virtual bool isDereferenceableOrNull(Value *O, const DataLayout &DL);
};

/// Determine what kind of capture behaviour \p U may exhibit.
Expand All @@ -171,12 +166,7 @@ namespace llvm {
///
/// \p Base is the starting value of the capture analysis, which is
/// relevant for address_is_null captures.
/// The \p IsDereferenceableOrNull callback is used to rule out capturing for
/// certain comparisons.
UseCaptureInfo
DetermineUseCaptureKind(const Use &U, const Value *Base,
llvm::function_ref<bool(Value *, const DataLayout &)>
IsDereferenceableOrNull);
UseCaptureInfo DetermineUseCaptureKind(const Use &U, const Value *Base);

/// PointerMayBeCaptured - Visit the value and the values derived from it and
/// find values which appear to be capturing the pointer value. This feeds
Expand Down
33 changes: 2 additions & 31 deletions llvm/lib/Analysis/CaptureTracking.cpp
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Expand Up @@ -56,21 +56,6 @@ CaptureTracker::~CaptureTracker() = default;

bool CaptureTracker::shouldExplore(const Use *U) { return true; }

bool CaptureTracker::isDereferenceableOrNull(Value *O, const DataLayout &DL) {
// We want comparisons to null pointers to not be considered capturing,
// but need to guard against cases like gep(p, -ptrtoint(p2)) == null,
// which are equivalent to p == p2 and would capture the pointer.
//
// A dereferenceable pointer is a case where this is known to be safe,
// because the pointer resulting from such a construction would not be
// dereferenceable.
//
// It is not sufficient to check for inbounds GEP here, because GEP with
// zero offset is always inbounds.
bool CanBeNull, CanBeFreed;
return O->getPointerDereferenceableBytes(DL, CanBeNull, CanBeFreed);
}

namespace {
struct SimpleCaptureTracker : public CaptureTracker {
explicit SimpleCaptureTracker(bool ReturnCaptures, CaptureComponents Mask,
Expand Down Expand Up @@ -281,9 +266,7 @@ Instruction *llvm::FindEarliestCapture(const Value *V, Function &F,
return CB.EarliestCapture;
}

UseCaptureInfo llvm::DetermineUseCaptureKind(
const Use &U, const Value *Base,
function_ref<bool(Value *, const DataLayout &)> IsDereferenceableOrNull) {
UseCaptureInfo llvm::DetermineUseCaptureKind(const Use &U, const Value *Base) {
Instruction *I = dyn_cast<Instruction>(U.getUser());

// TODO: Investigate non-instruction uses.
Expand Down Expand Up @@ -391,15 +374,6 @@ UseCaptureInfo llvm::DetermineUseCaptureKind(
if (U->getType()->getPointerAddressSpace() == 0)
if (isNoAliasCall(U.get()->stripPointerCasts()))
return CaptureComponents::None;
if (!I->getFunction()->nullPointerIsDefined()) {
auto *O = I->getOperand(Idx)->stripPointerCastsSameRepresentation();
// Comparing a dereferenceable_or_null pointer against null cannot
// lead to pointer escapes, because if it is not null it must be a
// valid (in-bounds) pointer.
const DataLayout &DL = I->getDataLayout();
if (IsDereferenceableOrNull && IsDereferenceableOrNull(O, DL))
return CaptureComponents::None;
}

// Check whether this is a comparison of the base pointer against
// null.
Expand Down Expand Up @@ -447,12 +421,9 @@ void llvm::PointerMayBeCaptured(const Value *V, CaptureTracker *Tracker,
if (!AddUses(V))
return;

auto IsDereferenceableOrNull = [Tracker](Value *V, const DataLayout &DL) {
return Tracker->isDereferenceableOrNull(V, DL);
};
while (!Worklist.empty()) {
const Use *U = Worklist.pop_back_val();
UseCaptureInfo CI = DetermineUseCaptureKind(*U, V, IsDereferenceableOrNull);
UseCaptureInfo CI = DetermineUseCaptureKind(*U, V);
if (capturesAnything(CI.UseCC)) {
switch (Tracker->captured(U, CI)) {
case CaptureTracker::Stop:
Expand Down
20 changes: 3 additions & 17 deletions llvm/lib/Transforms/IPO/AttributorAttributes.cpp
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Expand Up @@ -3928,12 +3928,6 @@ struct AANoAliasCallSiteArgument final : AANoAliasImpl {
// (iii) There is no other pointer argument which could alias with the
// value.

auto IsDereferenceableOrNull = [&](Value *O, const DataLayout &DL) {
const auto *DerefAA = A.getAAFor<AADereferenceable>(
*this, IRPosition::value(*O), DepClassTy::OPTIONAL);
return DerefAA ? DerefAA->getAssumedDereferenceableBytes() : 0;
};

const IRPosition &VIRP = IRPosition::value(getAssociatedValue());
const Function *ScopeFn = VIRP.getAnchorScope();
// Check whether the value is captured in the scope using AANoCapture.
Expand Down Expand Up @@ -3973,8 +3967,7 @@ struct AANoAliasCallSiteArgument final : AANoAliasImpl {
// is CGSCC runs. For those we would need to "allow" AANoCapture for
// a value in the module slice.
// TODO(captures): Make this more precise.
UseCaptureInfo CI =
DetermineUseCaptureKind(U, /*Base=*/nullptr, IsDereferenceableOrNull);
UseCaptureInfo CI = DetermineUseCaptureKind(U, /*Base=*/nullptr);
if (capturesNothing(CI))
return true;
if (CI.isPassthrough()) {
Expand Down Expand Up @@ -6035,16 +6028,9 @@ ChangeStatus AANoCaptureImpl::updateImpl(Attributor &A) {
}
}

auto IsDereferenceableOrNull = [&](Value *O, const DataLayout &DL) {
const auto *DerefAA = A.getAAFor<AADereferenceable>(
*this, IRPosition::value(*O), DepClassTy::OPTIONAL);
return DerefAA && DerefAA->getAssumedDereferenceableBytes();
};

auto UseCheck = [&](const Use &U, bool &Follow) -> bool {
// TODO(captures): Make this more precise.
UseCaptureInfo CI =
DetermineUseCaptureKind(U, /*Base=*/nullptr, IsDereferenceableOrNull);
UseCaptureInfo CI = DetermineUseCaptureKind(U, /*Base=*/nullptr);
if (capturesNothing(CI))
return true;
if (CI.isPassthrough()) {
Expand Down Expand Up @@ -12177,7 +12163,7 @@ struct AAGlobalValueInfoFloating : public AAGlobalValueInfo {
auto UsePred = [&](const Use &U, bool &Follow) -> bool {
Uses.insert(&U);
// TODO(captures): Make this more precise.
UseCaptureInfo CI = DetermineUseCaptureKind(U, /*Base=*/nullptr, nullptr);
UseCaptureInfo CI = DetermineUseCaptureKind(U, /*Base=*/nullptr);
if (CI.isPassthrough()) {
Follow = true;
return true;
Expand Down
9 changes: 1 addition & 8 deletions llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
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Expand Up @@ -1519,12 +1519,6 @@ bool MemCpyOptPass::performStackMoveOptzn(Instruction *Load, Instruction *Store,
SmallSet<Instruction *, 4> AAMetadataInstrs;
bool SrcNotDom = false;

// Recursively track the user and check whether modified alias exist.
auto IsDereferenceableOrNull = [](Value *V, const DataLayout &DL) -> bool {
bool CanBeNull, CanBeFreed;
return V->getPointerDereferenceableBytes(DL, CanBeNull, CanBeFreed);
};

auto CaptureTrackingWithModRef =
[&](Instruction *AI,
function_ref<bool(Instruction *)> ModRefCallback) -> bool {
Expand All @@ -1551,8 +1545,7 @@ bool MemCpyOptPass::performStackMoveOptzn(Instruction *Load, Instruction *Store,
}
if (!Visited.insert(&U).second)
continue;
UseCaptureInfo CI =
DetermineUseCaptureKind(U, AI, IsDereferenceableOrNull);
UseCaptureInfo CI = DetermineUseCaptureKind(U, AI);
// TODO(captures): Make this more precise.
if (capturesAnything(CI.UseCC))
return false;
Expand Down
2 changes: 1 addition & 1 deletion llvm/test/Transforms/Attributor/nocapture-1.ll
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Expand Up @@ -741,7 +741,7 @@ define i1 @nocaptureInboundsGEPICmpRev(ptr %x) {
define i1 @nocaptureDereferenceableOrNullICmp(ptr dereferenceable_or_null(4) %x) {
; CHECK: Function Attrs: mustprogress nofree norecurse nosync nounwind willreturn memory(none)
; CHECK-LABEL: define {{[^@]+}}@nocaptureDereferenceableOrNullICmp
; CHECK-SAME: (ptr nofree noundef readnone captures(none) dereferenceable_or_null(4) [[X:%.*]]) #[[ATTR0]] {
; CHECK-SAME: (ptr nofree noundef readnone dereferenceable_or_null(4) [[X:%.*]]) #[[ATTR0]] {
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Attributor results are currently not optimal because it just generally doesn't support captures, tracked in #135610.

; CHECK-NEXT: [[TMP1:%.*]] = icmp eq ptr [[X]], null
; CHECK-NEXT: ret i1 [[TMP1]]
;
Expand Down
26 changes: 13 additions & 13 deletions llvm/test/Transforms/Attributor/nocapture-2.ll
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Expand Up @@ -164,14 +164,14 @@ entry:
define ptr @scc_A(ptr dereferenceable_or_null(4) %a) {
; CHECK: Function Attrs: nofree nosync nounwind memory(none)
; CHECK-LABEL: define noundef dereferenceable_or_null(4) ptr @scc_A
; CHECK-SAME: (ptr nofree noundef readnone returned dereferenceable_or_null(4) "no-capture-maybe-returned" [[A:%.*]]) #[[ATTR2:[0-9]+]] {
; CHECK-SAME: (ptr nofree noundef readnone returned dereferenceable_or_null(4) [[A:%.*]]) #[[ATTR2:[0-9]+]] {
; CHECK-NEXT: entry:
; CHECK-NEXT: [[TOBOOL:%.*]] = icmp ne ptr [[A]], null
; CHECK-NEXT: br i1 [[TOBOOL]], label [[COND_TRUE:%.*]], label [[COND_FALSE:%.*]]
; CHECK: cond.true:
; CHECK-NEXT: [[CALL:%.*]] = call dereferenceable_or_null(4) ptr @scc_C(ptr noalias nofree noundef nonnull readnone dereferenceable(4) "no-capture-maybe-returned" [[A]]) #[[ATTR2]]
; CHECK-NEXT: [[CALL1:%.*]] = call dereferenceable_or_null(8) ptr @scc_B(ptr noalias nofree noundef readnone dereferenceable_or_null(8) "no-capture-maybe-returned" [[A]]) #[[ATTR2]]
; CHECK-NEXT: [[CALL2:%.*]] = call ptr @scc_A(ptr noalias nofree noundef readnone dereferenceable_or_null(8) "no-capture-maybe-returned" [[A]]) #[[ATTR2]]
; CHECK-NEXT: [[CALL:%.*]] = call dereferenceable_or_null(4) ptr @scc_C(ptr noalias nofree noundef nonnull readnone dereferenceable(4) [[A]]) #[[ATTR2]]
; CHECK-NEXT: [[CALL1:%.*]] = call dereferenceable_or_null(8) ptr @scc_B(ptr noalias nofree noundef readnone dereferenceable_or_null(8) [[A]]) #[[ATTR2]]
; CHECK-NEXT: [[CALL2:%.*]] = call ptr @scc_A(ptr noalias nofree noundef readnone dereferenceable_or_null(8) [[A]]) #[[ATTR2]]
; CHECK-NEXT: br label [[COND_END:%.*]]
; CHECK: cond.false:
; CHECK-NEXT: br label [[COND_END]]
Expand Down Expand Up @@ -201,14 +201,14 @@ cond.end: ; preds = %cond.false, %cond.t
define ptr @scc_B(ptr dereferenceable_or_null(8) %a) {
; CHECK: Function Attrs: nofree nosync nounwind memory(none)
; CHECK-LABEL: define noundef dereferenceable_or_null(8) ptr @scc_B
; CHECK-SAME: (ptr nofree noundef readnone returned dereferenceable_or_null(8) "no-capture-maybe-returned" [[A:%.*]]) #[[ATTR2]] {
; CHECK-SAME: (ptr nofree noundef readnone returned dereferenceable_or_null(8) [[A:%.*]]) #[[ATTR2]] {
; CHECK-NEXT: entry:
; CHECK-NEXT: [[TOBOOL:%.*]] = icmp ne ptr [[A]], null
; CHECK-NEXT: br i1 [[TOBOOL]], label [[COND_TRUE:%.*]], label [[COND_FALSE:%.*]]
; CHECK: cond.true:
; CHECK-NEXT: [[CALL:%.*]] = call dereferenceable_or_null(4) ptr @scc_A(ptr noalias nofree noundef nonnull readnone dereferenceable(8) "no-capture-maybe-returned" [[A]]) #[[ATTR2]]
; CHECK-NEXT: [[CALL1:%.*]] = call dereferenceable_or_null(8) ptr @scc_B(ptr noalias nofree noundef readnone dereferenceable_or_null(8) "no-capture-maybe-returned" [[A]]) #[[ATTR2]]
; CHECK-NEXT: [[CALL2:%.*]] = call ptr @scc_C(ptr noalias nofree noundef readnone dereferenceable_or_null(8) "no-capture-maybe-returned" [[A]]) #[[ATTR2]]
; CHECK-NEXT: [[CALL:%.*]] = call dereferenceable_or_null(4) ptr @scc_A(ptr noalias nofree noundef nonnull readnone dereferenceable(8) [[A]]) #[[ATTR2]]
; CHECK-NEXT: [[CALL1:%.*]] = call dereferenceable_or_null(8) ptr @scc_B(ptr noalias nofree noundef readnone dereferenceable_or_null(8) [[A]]) #[[ATTR2]]
; CHECK-NEXT: [[CALL2:%.*]] = call ptr @scc_C(ptr noalias nofree noundef readnone dereferenceable_or_null(8) [[A]]) #[[ATTR2]]
; CHECK-NEXT: br label [[COND_END:%.*]]
; CHECK: cond.false:
; CHECK-NEXT: br label [[COND_END]]
Expand Down Expand Up @@ -237,20 +237,20 @@ cond.end: ; preds = %cond.false, %cond.t
define ptr @scc_C(ptr dereferenceable_or_null(2) %a) {
; CHECK: Function Attrs: nofree nosync nounwind memory(none)
; CHECK-LABEL: define noundef dereferenceable_or_null(4) ptr @scc_C
; CHECK-SAME: (ptr nofree noundef readnone returned dereferenceable_or_null(4) "no-capture-maybe-returned" [[A:%.*]]) #[[ATTR2]] {
; CHECK-SAME: (ptr nofree noundef readnone returned dereferenceable_or_null(4) [[A:%.*]]) #[[ATTR2]] {
; CHECK-NEXT: entry:
; CHECK-NEXT: [[CALL:%.*]] = call dereferenceable_or_null(4) ptr @scc_A(ptr noalias nofree noundef readnone dereferenceable_or_null(4) "no-capture-maybe-returned" [[A]]) #[[ATTR2]]
; CHECK-NEXT: [[CALL:%.*]] = call ptr @scc_A(ptr noalias nofree noundef readnone dereferenceable_or_null(4) [[A]]) #[[ATTR2]]
; CHECK-NEXT: [[TOBOOL:%.*]] = icmp ne ptr [[A]], null
; CHECK-NEXT: br i1 [[TOBOOL]], label [[COND_TRUE:%.*]], label [[COND_FALSE:%.*]]
; CHECK: cond.true:
; CHECK-NEXT: [[CALL1:%.*]] = call ptr @scc_B(ptr noalias nofree noundef readnone dereferenceable_or_null(8) "no-capture-maybe-returned" [[A]]) #[[ATTR2]]
; CHECK-NEXT: [[CALL1:%.*]] = call ptr @scc_B(ptr noalias nofree noundef readnone dereferenceable_or_null(8) [[A]]) #[[ATTR2]]
; CHECK-NEXT: br label [[COND_END:%.*]]
; CHECK: cond.false:
; CHECK-NEXT: [[CALL2:%.*]] = call ptr @scc_C(ptr noalias nofree noundef readnone dereferenceable_or_null(4) "no-capture-maybe-returned" [[A]]) #[[ATTR2]]
; CHECK-NEXT: [[CALL2:%.*]] = call ptr @scc_C(ptr noalias nofree noundef readnone dereferenceable_or_null(4) [[A]]) #[[ATTR2]]
; CHECK-NEXT: br label [[COND_END]]
; CHECK: cond.end:
; CHECK-NEXT: [[COND:%.*]] = phi ptr [ [[A]], [[COND_TRUE]] ], [ [[A]], [[COND_FALSE]] ]
; CHECK-NEXT: [[CALL3:%.*]] = call ptr @scc_A(ptr noalias nofree noundef readnone dereferenceable_or_null(4) "no-capture-maybe-returned" [[A]]) #[[ATTR2]]
; CHECK-NEXT: [[CALL3:%.*]] = call ptr @scc_A(ptr noalias nofree noundef readnone dereferenceable_or_null(4) [[A]]) #[[ATTR2]]
; CHECK-NEXT: ret ptr [[A]]
;
entry:
Expand Down
2 changes: 1 addition & 1 deletion llvm/test/Transforms/FunctionAttrs/nocapture.ll
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Expand Up @@ -960,7 +960,7 @@ define i1 @inboundsGEPICmpNullPointerDefined(ptr %x) null_pointer_is_valid {
define i1 @nocaptureDereferenceableOrNullICmp(ptr dereferenceable_or_null(4) %x) {
; FNATTRS: Function Attrs: mustprogress nofree norecurse nosync nounwind willreturn memory(none)
; FNATTRS-LABEL: define noundef i1 @nocaptureDereferenceableOrNullICmp
; FNATTRS-SAME: (ptr readnone captures(none) dereferenceable_or_null(4) [[X:%.*]]) #[[ATTR0]] {
; FNATTRS-SAME: (ptr readnone captures(address_is_null) dereferenceable_or_null(4) [[X:%.*]]) #[[ATTR0]] {
; FNATTRS-NEXT: [[TMP1:%.*]] = icmp eq ptr [[X]], null
; FNATTRS-NEXT: ret i1 [[TMP1]]
;
Expand Down
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