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[LAA] Always require non-wrapping pointers for runtime checks. #127543

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Feb 20, 2025
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[LAA] Always require non-wrapping pointers for runtime checks. #127543

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41 changes: 19 additions & 22 deletions llvm/lib/Analysis/LoopAccessAnalysis.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -677,16 +677,17 @@ class AccessAnalysis {
const DenseMap<Value *, const SCEV *> &Strides,
DenseMap<Value *, unsigned> &DepSetId,
Loop *TheLoop, unsigned &RunningDepId,
unsigned ASId, bool ShouldCheckStride, bool Assume);
unsigned ASId, bool Assume);

/// Check whether we can check the pointers at runtime for
/// non-intersection.
///
/// Returns true if we need no check or if we do and we can generate them
/// (i.e. the pointers have computable bounds).
bool canCheckPtrAtRT(RuntimePointerChecking &RtCheck, ScalarEvolution *SE,
Loop *TheLoop, const DenseMap<Value *, const SCEV *> &Strides,
Value *&UncomputablePtr, bool ShouldCheckWrap = false);
Loop *TheLoop,
const DenseMap<Value *, const SCEV *> &Strides,
Value *&UncomputablePtr);

/// Goes over all memory accesses, checks whether a RT check is needed
/// and builds sets of dependent accesses.
Expand Down Expand Up @@ -1115,13 +1116,11 @@ findForkedPointer(PredicatedScalarEvolution &PSE,
return {{replaceSymbolicStrideSCEV(PSE, StridesMap, Ptr), false}};
}

bool AccessAnalysis::createCheckForAccess(RuntimePointerChecking &RtCheck,
MemAccessInfo Access, Type *AccessTy,
const DenseMap<Value *, const SCEV *> &StridesMap,
DenseMap<Value *, unsigned> &DepSetId,
Loop *TheLoop, unsigned &RunningDepId,
unsigned ASId, bool ShouldCheckWrap,
bool Assume) {
bool AccessAnalysis::createCheckForAccess(
RuntimePointerChecking &RtCheck, MemAccessInfo Access, Type *AccessTy,
const DenseMap<Value *, const SCEV *> &StridesMap,
DenseMap<Value *, unsigned> &DepSetId, Loop *TheLoop,
unsigned &RunningDepId, unsigned ASId, bool Assume) {
Value *Ptr = Access.getPointer();

SmallVector<PointerIntPair<const SCEV *, 1, bool>> TranslatedPtrs =
Expand Down Expand Up @@ -1152,8 +1151,7 @@ bool AccessAnalysis::createCheckForAccess(RuntimePointerChecking &RtCheck,

// When we run after a failing dependency check we have to make sure
// we don't have wrapping pointers.
if (ShouldCheckWrap &&
!isNoWrap(PSE, AR, TranslatedPtrs.size() == 1 ? Ptr : nullptr, AccessTy,
if (!isNoWrap(PSE, AR, TranslatedPtrs.size() == 1 ? Ptr : nullptr, AccessTy,
TheLoop, Assume)) {
return false;
}
Expand Down Expand Up @@ -1182,10 +1180,10 @@ bool AccessAnalysis::createCheckForAccess(RuntimePointerChecking &RtCheck,
return true;
}

bool AccessAnalysis::canCheckPtrAtRT(RuntimePointerChecking &RtCheck,
ScalarEvolution *SE, Loop *TheLoop,
const DenseMap<Value *, const SCEV *> &StridesMap,
Value *&UncomputablePtr, bool ShouldCheckWrap) {
bool AccessAnalysis::canCheckPtrAtRT(
RuntimePointerChecking &RtCheck, ScalarEvolution *SE, Loop *TheLoop,
const DenseMap<Value *, const SCEV *> &StridesMap,
Value *&UncomputablePtr) {
// Find pointers with computable bounds. We are going to use this information
// to place a runtime bound check.
bool CanDoRT = true;
Expand Down Expand Up @@ -1245,7 +1243,7 @@ bool AccessAnalysis::canCheckPtrAtRT(RuntimePointerChecking &RtCheck,
for (const auto &AccessTy : Accesses[Access]) {
if (!createCheckForAccess(RtCheck, Access, AccessTy, StridesMap,
DepSetId, TheLoop, RunningDepId, ASId,
ShouldCheckWrap, false)) {
false)) {
LLVM_DEBUG(dbgs() << "LAA: Can't find bounds for ptr:"
<< *Access.getPointer() << '\n');
Retries.emplace_back(Access, AccessTy);
Expand Down Expand Up @@ -1275,7 +1273,7 @@ bool AccessAnalysis::canCheckPtrAtRT(RuntimePointerChecking &RtCheck,
for (const auto &[Access, AccessTy] : Retries) {
if (!createCheckForAccess(RtCheck, Access, AccessTy, StridesMap,
DepSetId, TheLoop, RunningDepId, ASId,
ShouldCheckWrap, /*Assume=*/true)) {
/*Assume=*/true)) {
CanDoAliasSetRT = false;
UncomputablePtr = Access.getPointer();
break;
Expand Down Expand Up @@ -2643,9 +2641,8 @@ bool LoopAccessInfo::analyzeLoop(AAResults *AA, const LoopInfo *LI,
// Find pointers with computable bounds. We are going to use this information
// to place a runtime bound check.
Value *UncomputablePtr = nullptr;
bool CanDoRTIfNeeded =
Accesses.canCheckPtrAtRT(*PtrRtChecking, PSE->getSE(), TheLoop,
SymbolicStrides, UncomputablePtr, false);
bool CanDoRTIfNeeded = Accesses.canCheckPtrAtRT(
*PtrRtChecking, PSE->getSE(), TheLoop, SymbolicStrides, UncomputablePtr);
if (!CanDoRTIfNeeded) {
const auto *I = dyn_cast_or_null<Instruction>(UncomputablePtr);
recordAnalysis("CantIdentifyArrayBounds", I)
Expand Down Expand Up @@ -2676,7 +2673,7 @@ bool LoopAccessInfo::analyzeLoop(AAResults *AA, const LoopInfo *LI,
auto *SE = PSE->getSE();
UncomputablePtr = nullptr;
CanDoRTIfNeeded = Accesses.canCheckPtrAtRT(
*PtrRtChecking, SE, TheLoop, SymbolicStrides, UncomputablePtr, true);
*PtrRtChecking, SE, TheLoop, SymbolicStrides, UncomputablePtr);

// Check that we found the bounds for the pointer.
if (!CanDoRTIfNeeded) {
Expand Down
30 changes: 18 additions & 12 deletions llvm/test/Analysis/LoopAccessAnalysis/nusw-predicates.ll
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Expand Up @@ -15,6 +15,12 @@ define void @int_and_pointer_predicate(ptr %v, i32 %N) {
; CHECK-EMPTY:
; CHECK-NEXT: Run-time memory checks:
; CHECK-NEXT: Grouped accesses:
; CHECK-NEXT: Group [[GRP1:0x[0-9a-f]+]]:
; CHECK-NEXT: (Low: %v High: (2 + %v))
; CHECK-NEXT: Member: %v
; CHECK-NEXT: Group [[GRP2:0x[0-9a-f]+]]:
; CHECK-NEXT: (Low: %v High: (6 + (4 * (trunc i32 %N to i16)) + %v))
; CHECK-NEXT: Member: {%v,+,4}<%loop>
; CHECK-EMPTY:
; CHECK-NEXT: Non vectorizable stores to invariant address were not found in loop.
; CHECK-NEXT: SCEV assumptions:
Expand Down Expand Up @@ -57,36 +63,36 @@ define void @int_and_multiple_pointer_predicates(ptr %v, ptr %w, i32 %N) {
; CHECK-EMPTY:
; CHECK-NEXT: Run-time memory checks:
; CHECK-NEXT: Check 0:
; CHECK-NEXT: Comparing group ([[GRP1:0x[0-9a-f]+]]):
; CHECK-NEXT: Comparing group ([[GRP3:0x[0-9a-f]+]]):
; CHECK-NEXT: ptr %v
; CHECK-NEXT: Against group ([[GRP2:0x[0-9a-f]+]]):
; CHECK-NEXT: Against group ([[GRP4:0x[0-9a-f]+]]):
; CHECK-NEXT: ptr %w
; CHECK-NEXT: Check 1:
; CHECK-NEXT: Comparing group ([[GRP1]]):
; CHECK-NEXT: Comparing group ([[GRP3]]):
; CHECK-NEXT: ptr %v
; CHECK-NEXT: Against group ([[GRP3:0x[0-9a-f]+]]):
; CHECK-NEXT: Against group ([[GRP5:0x[0-9a-f]+]]):
; CHECK-NEXT: %gep.w = getelementptr { i16, i16 }, ptr %w, i16 %iv.i16
; CHECK-NEXT: Check 2:
; CHECK-NEXT: Comparing group ([[GRP4:0x[0-9a-f]+]]):
; CHECK-NEXT: Comparing group ([[GRP6:0x[0-9a-f]+]]):
; CHECK-NEXT: %gep.v = getelementptr { i16, i16 }, ptr %v, i16 %iv.i16
; CHECK-NEXT: Against group ([[GRP2]]):
; CHECK-NEXT: Against group ([[GRP4]]):
; CHECK-NEXT: ptr %w
; CHECK-NEXT: Check 3:
; CHECK-NEXT: Comparing group ([[GRP4]]):
; CHECK-NEXT: Comparing group ([[GRP6]]):
; CHECK-NEXT: %gep.v = getelementptr { i16, i16 }, ptr %v, i16 %iv.i16
; CHECK-NEXT: Against group ([[GRP3]]):
; CHECK-NEXT: Against group ([[GRP5]]):
; CHECK-NEXT: %gep.w = getelementptr { i16, i16 }, ptr %w, i16 %iv.i16
; CHECK-NEXT: Grouped accesses:
; CHECK-NEXT: Group [[GRP1]]:
; CHECK-NEXT: Group [[GRP3]]:
; CHECK-NEXT: (Low: %v High: (2 + %v))
; CHECK-NEXT: Member: %v
; CHECK-NEXT: Group [[GRP4]]:
; CHECK-NEXT: Group [[GRP6]]:
; CHECK-NEXT: (Low: %v High: (6 + (4 * (trunc i32 %N to i16)) + %v))
; CHECK-NEXT: Member: {%v,+,4}<%loop>
; CHECK-NEXT: Group [[GRP2]]:
; CHECK-NEXT: Group [[GRP4]]:
; CHECK-NEXT: (Low: %w High: (2 + %w))
; CHECK-NEXT: Member: %w
; CHECK-NEXT: Group [[GRP3]]:
; CHECK-NEXT: Group [[GRP5]]:
; CHECK-NEXT: (Low: %w High: (6 + (4 * (trunc i32 %N to i16)) + %w))
; CHECK-NEXT: Member: {%w,+,4}<%loop>
; CHECK-EMPTY:
Expand Down
4 changes: 2 additions & 2 deletions ...ysis/LoopAccessAnalysis/retry-runtime-checks-after-dependence-analysis-forked-pointers.ll
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Expand Up @@ -163,7 +163,7 @@ exit:
define void @dependency_check_and_runtime_checks_needed_select_of_ptr_add_recs_may_wrap_1(ptr %a, ptr %b, ptr %c, i64 %offset, i64 %n) {
; CHECK-LABEL: 'dependency_check_and_runtime_checks_needed_select_of_ptr_add_recs_may_wrap_1'
; CHECK-NEXT: loop:
; CHECK-NEXT: Report: cannot check memory dependencies at runtime
; CHECK-NEXT: Report: cannot identify array bounds
; CHECK-NEXT: Dependences:
; CHECK-NEXT: Run-time memory checks:
; CHECK-NEXT: Grouped accesses:
Expand Down Expand Up @@ -204,7 +204,7 @@ exit:
define void @dependency_check_and_runtime_checks_needed_select_of_ptr_add_recs_may_wrap_2(ptr %a, ptr %b, ptr %c, i64 %offset, i64 %n) {
; CHECK-LABEL: 'dependency_check_and_runtime_checks_needed_select_of_ptr_add_recs_may_wrap_2'
; CHECK-NEXT: loop:
; CHECK-NEXT: Report: cannot check memory dependencies at runtime
; CHECK-NEXT: Report: cannot identify array bounds
; CHECK-NEXT: Dependences:
; CHECK-NEXT: Run-time memory checks:
; CHECK-NEXT: Grouped accesses:
Expand Down
28 changes: 14 additions & 14 deletions llvm/test/Analysis/LoopAccessAnalysis/retry-runtime-checks-after-dependence-analysis.ll
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Expand Up @@ -72,27 +72,27 @@ define void @dependency_check_and_runtime_checks_needed_gepb_not_inbounds_iv2_st
; CHECK-NEXT: Comparing group ([[GRP4:0x[0-9a-f]+]]):
; CHECK-NEXT: %gep.a.iv = getelementptr inbounds float, ptr %a, i64 %iv
; CHECK-NEXT: Against group ([[GRP5:0x[0-9a-f]+]]):
; CHECK-NEXT: %gep.a.iv.off = getelementptr inbounds float, ptr %a, i64 %iv.offset
; CHECK-NEXT: %gep.b = getelementptr i8, ptr %b, i64 %iv2
; CHECK-NEXT: Check 1:
; CHECK-NEXT: Comparing group ([[GRP4]]):
; CHECK-NEXT: %gep.a.iv = getelementptr inbounds float, ptr %a, i64 %iv
; CHECK-NEXT: Against group ([[GRP6:0x[0-9a-f]+]]):
; CHECK-NEXT: %gep.b = getelementptr i8, ptr %b, i64 %iv2
; CHECK-NEXT: %gep.a.iv.off = getelementptr inbounds float, ptr %a, i64 %iv.offset
; CHECK-NEXT: Check 2:
; CHECK-NEXT: Comparing group ([[GRP5]]):
; CHECK-NEXT: %gep.a.iv.off = getelementptr inbounds float, ptr %a, i64 %iv.offset
; CHECK-NEXT: Against group ([[GRP6]]):
; CHECK-NEXT: %gep.b = getelementptr i8, ptr %b, i64 %iv2
; CHECK-NEXT: Against group ([[GRP6]]):
; CHECK-NEXT: %gep.a.iv.off = getelementptr inbounds float, ptr %a, i64 %iv.offset
; CHECK-NEXT: Grouped accesses:
; CHECK-NEXT: Group [[GRP4]]:
; CHECK-NEXT: (Low: %a High: ((4 * %n) + %a))
; CHECK-NEXT: Member: {%a,+,4}<nuw><%loop>
; CHECK-NEXT: Group [[GRP5]]:
; CHECK-NEXT: (Low: ((4 * %offset) + %a) High: ((4 * %offset) + (4 * %n) + %a))
; CHECK-NEXT: Member: {((4 * %offset) + %a),+,4}<%loop>
; CHECK-NEXT: Group [[GRP6]]:
; CHECK-NEXT: (Low: %b High: (-1 + (5 * %n) + %b))
; CHECK-NEXT: Member: {%b,+,5}<%loop>
; CHECK-NEXT: Group [[GRP6]]:
; CHECK-NEXT: (Low: ((4 * %offset) + %a) High: ((4 * %offset) + (4 * %n) + %a))
; CHECK-NEXT: Member: {((4 * %offset) + %a),+,4}<%loop>
; CHECK-EMPTY:
; CHECK-NEXT: Non vectorizable stores to invariant address were not found in loop.
; CHECK-NEXT: SCEV assumptions:
Expand Down Expand Up @@ -265,27 +265,27 @@ define void @dependency_check_and_runtime_checks_needed_gepb_may_wrap(ptr %a, pt
; CHECK-NEXT: Comparing group ([[GRP13:0x[0-9a-f]+]]):
; CHECK-NEXT: %gep.a.iv = getelementptr inbounds float, ptr %a, i64 %iv
; CHECK-NEXT: Against group ([[GRP14:0x[0-9a-f]+]]):
; CHECK-NEXT: %gep.a.iv.off = getelementptr inbounds float, ptr %a, i64 %iv.offset
; CHECK-NEXT: %gep.b = getelementptr float, ptr %b, i64 %iv2
; CHECK-NEXT: Check 1:
; CHECK-NEXT: Comparing group ([[GRP13]]):
; CHECK-NEXT: %gep.a.iv = getelementptr inbounds float, ptr %a, i64 %iv
; CHECK-NEXT: Against group ([[GRP15:0x[0-9a-f]+]]):
; CHECK-NEXT: %gep.b = getelementptr float, ptr %b, i64 %iv2
; CHECK-NEXT: %gep.a.iv.off = getelementptr inbounds float, ptr %a, i64 %iv.offset
; CHECK-NEXT: Check 2:
; CHECK-NEXT: Comparing group ([[GRP14]]):
; CHECK-NEXT: %gep.a.iv.off = getelementptr inbounds float, ptr %a, i64 %iv.offset
; CHECK-NEXT: Against group ([[GRP15]]):
; CHECK-NEXT: %gep.b = getelementptr float, ptr %b, i64 %iv2
; CHECK-NEXT: Against group ([[GRP15]]):
; CHECK-NEXT: %gep.a.iv.off = getelementptr inbounds float, ptr %a, i64 %iv.offset
; CHECK-NEXT: Grouped accesses:
; CHECK-NEXT: Group [[GRP13]]:
; CHECK-NEXT: (Low: %a High: ((4 * %n) + %a))
; CHECK-NEXT: Member: {%a,+,4}<nuw><%loop>
; CHECK-NEXT: Group [[GRP14]]:
; CHECK-NEXT: (Low: ((4 * %offset) + %a) High: ((4 * %offset) + (4 * %n) + %a))
; CHECK-NEXT: Member: {((4 * %offset) + %a),+,4}<%loop>
; CHECK-NEXT: Group [[GRP15]]:
; CHECK-NEXT: (Low: %b High: (-4 + (8 * %n) + %b))
; CHECK-NEXT: Member: {%b,+,8}<%loop>
; CHECK-NEXT: Group [[GRP15]]:
; CHECK-NEXT: (Low: ((4 * %offset) + %a) High: ((4 * %offset) + (4 * %n) + %a))
; CHECK-NEXT: Member: {((4 * %offset) + %a),+,4}<%loop>
; CHECK-EMPTY:
; CHECK-NEXT: Non vectorizable stores to invariant address were not found in loop.
; CHECK-NEXT: SCEV assumptions:
Expand Down
11 changes: 6 additions & 5 deletions llvm/test/Analysis/LoopAccessAnalysis/runtime-checks-may-wrap.ll
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Expand Up @@ -11,20 +11,21 @@ define void @geps_may_wrap(ptr %a, ptr %b, i64 %N) {
; CHECK-NEXT: Run-time memory checks:
; CHECK-NEXT: Check 0:
; CHECK-NEXT: Comparing group ([[GRP1:0x[0-9a-f]+]]):
; CHECK-NEXT: %gep.iv = getelementptr i32, ptr %a, i64 %iv
; CHECK-NEXT: Against group ([[GRP2:0x[0-9a-f]+]]):
; CHECK-NEXT: ptr %b
; CHECK-NEXT: Against group ([[GRP2:0x[0-9a-f]+]]):
; CHECK-NEXT: %gep.iv = getelementptr i32, ptr %a, i64 %iv
; CHECK-NEXT: Grouped accesses:
; CHECK-NEXT: Group [[GRP1]]:
; CHECK-NEXT: (Low: %a High: (16 + (12 * (trunc i128 ((zext i64 %N to i128) /u 3) to i16)) + %a))
; CHECK-NEXT: Member: {%a,+,12}<%loop>
; CHECK-NEXT: Group [[GRP2]]:
; CHECK-NEXT: (Low: %b High: (4 + %b))
; CHECK-NEXT: Member: %b
; CHECK-NEXT: Group [[GRP2]]:
; CHECK-NEXT: (Low: %a High: (16 + (12 * (trunc i128 ((zext i64 %N to i128) /u 3) to i16)) + %a))
; CHECK-NEXT: Member: {%a,+,12}<%loop>
; CHECK-EMPTY:
; CHECK-NEXT: Non vectorizable stores to invariant address were not found in loop.
; CHECK-NEXT: SCEV assumptions:
; CHECK-NEXT: {0,+,3}<%loop> Added Flags: <nusw>
; CHECK-NEXT: {%a,+,12}<%loop> Added Flags: <nusw>
; CHECK-EMPTY:
; CHECK-NEXT: Expressions re-written:
;
Expand Down
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