Skip to content

[ConstantFolding] Consolidate poison propagation for intrinsics #146878

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
merged 4 commits into from
Jul 4, 2025
Merged

[ConstantFolding] Consolidate poison propagation for intrinsics #146878

Show file tree
Hide file tree
Changes from 3 commits
Commits
Show all changes
4 commits
Select commit Hold shift + click to select a range
c1c32e2
Add test for ctpop with poison arg
nikic Jul 3, 2025
f867100
Consolidate poison constant folding
nikic Jul 3, 2025
6c1ed11
Adjust unit test
nikic Jul 3, 2025
95ab15c
Use IsaPred
nikic Jul 3, 2025
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
3 changes: 3 additions & 0 deletions llvm/include/llvm/Analysis/ValueTracking.h
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -727,6 +727,9 @@ LLVM_ABI bool isGuaranteedToExecuteForEveryIteration(const Instruction *I,
/// getGuaranteedNonPoisonOp.
LLVM_ABI bool propagatesPoison(const Use &PoisonOp);

/// Return whether this intrinsic propagates poison for all operands.
LLVM_ABI bool intrinsicPropagatesPoison(Intrinsic::ID IID);

/// Return true if the given instruction must trigger undefined behavior
/// when I is executed with any operands which appear in KnownPoison holding
/// a poison value at the point of execution.
Expand Down
39 changes: 5 additions & 34 deletions llvm/lib/Analysis/ConstantFolding.cpp
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -2229,17 +2229,6 @@ static Constant *ConstantFoldScalarCall1(StringRef Name,
return nullptr;
}

if (isa<PoisonValue>(Operands[0])) {
// TODO: All of these operations should probably propagate poison.
switch (IntrinsicID) {
case Intrinsic::canonicalize:
case Intrinsic::sqrt:
return PoisonValue::get(Ty);
default:
break;
}
}

if (isa<UndefValue>(Operands[0])) {
// cosine(arg) is between -1 and 1. cosine(invalid arg) is NaN.
// ctpop() is between 0 and bitwidth, pick 0 for undef.
Expand Down Expand Up @@ -3228,11 +3217,6 @@ static Constant *ConstantFoldIntrinsicCall2(Intrinsic::ID IntrinsicID, Type *Ty,
case Intrinsic::smin:
case Intrinsic::umax:
case Intrinsic::umin:
// This is the same as for binary ops - poison propagates.
// TODO: Poison handling should be consolidated.
if (isa<PoisonValue>(Operands[0]) || isa<PoisonValue>(Operands[1]))
return PoisonValue::get(Ty);

if (!C0 && !C1)
return UndefValue::get(Ty);
if (!C0 || !C1)
Expand All @@ -3245,9 +3229,6 @@ static Constant *ConstantFoldIntrinsicCall2(Intrinsic::ID IntrinsicID, Type *Ty,

case Intrinsic::scmp:
case Intrinsic::ucmp:
if (isa<PoisonValue>(Operands[0]) || isa<PoisonValue>(Operands[1]))
return PoisonValue::get(Ty);

if (!C0 || !C1)
return ConstantInt::get(Ty, 0);

Expand Down Expand Up @@ -3314,11 +3295,6 @@ static Constant *ConstantFoldIntrinsicCall2(Intrinsic::ID IntrinsicID, Type *Ty,
}
case Intrinsic::uadd_sat:
case Intrinsic::sadd_sat:
// This is the same as for binary ops - poison propagates.
// TODO: Poison handling should be consolidated.
if (isa<PoisonValue>(Operands[0]) || isa<PoisonValue>(Operands[1]))
return PoisonValue::get(Ty);

if (!C0 && !C1)
return UndefValue::get(Ty);
if (!C0 || !C1)
Expand All @@ -3329,11 +3305,6 @@ static Constant *ConstantFoldIntrinsicCall2(Intrinsic::ID IntrinsicID, Type *Ty,
return ConstantInt::get(Ty, C0->sadd_sat(*C1));
case Intrinsic::usub_sat:
case Intrinsic::ssub_sat:
// This is the same as for binary ops - poison propagates.
// TODO: Poison handling should be consolidated.
if (isa<PoisonValue>(Operands[0]) || isa<PoisonValue>(Operands[1]))
return PoisonValue::get(Ty);

if (!C0 && !C1)
return UndefValue::get(Ty);
if (!C0 || !C1)
Expand Down Expand Up @@ -3592,11 +3563,6 @@ static Constant *ConstantFoldScalarCall3(StringRef Name,

if (IntrinsicID == Intrinsic::smul_fix ||
IntrinsicID == Intrinsic::smul_fix_sat) {
// poison * C -> poison
// C * poison -> poison
if (isa<PoisonValue>(Operands[0]) || isa<PoisonValue>(Operands[1]))
return PoisonValue::get(Ty);

const APInt *C0, *C1;
if (!getConstIntOrUndef(Operands[0], C0) ||
!getConstIntOrUndef(Operands[1], C1))
Expand Down Expand Up @@ -3670,6 +3636,11 @@ static Constant *ConstantFoldScalarCall(StringRef Name,
ArrayRef<Constant *> Operands,
const TargetLibraryInfo *TLI,
const CallBase *Call) {
if (IntrinsicID != Intrinsic::not_intrinsic &&
any_of(Operands, [](Constant *Op) { return isa<PoisonValue>(Op); }) &&
intrinsicPropagatesPoison(IntrinsicID))
return PoisonValue::get(Ty);

if (Operands.size() == 1)
return ConstantFoldScalarCall1(Name, IntrinsicID, Ty, Operands, TLI, Call);

Expand Down
75 changes: 43 additions & 32 deletions llvm/lib/Analysis/ValueTracking.cpp
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -7879,6 +7879,47 @@ bool llvm::isGuaranteedToExecuteForEveryIteration(const Instruction *I,
llvm_unreachable("Instruction not contained in its own parent basic block.");
}

bool llvm::intrinsicPropagatesPoison(Intrinsic::ID IID) {
switch (IID) {
// TODO: Add more intrinsics.
case Intrinsic::sadd_with_overflow:
case Intrinsic::ssub_with_overflow:
case Intrinsic::smul_with_overflow:
case Intrinsic::uadd_with_overflow:
case Intrinsic::usub_with_overflow:
case Intrinsic::umul_with_overflow:
// If an input is a vector containing a poison element, the
// two output vectors (calculated results, overflow bits)'
// corresponding lanes are poison.
return true;
case Intrinsic::ctpop:
case Intrinsic::ctlz:
case Intrinsic::cttz:
case Intrinsic::abs:
case Intrinsic::smax:
case Intrinsic::smin:
case Intrinsic::umax:
case Intrinsic::umin:
case Intrinsic::scmp:
case Intrinsic::ucmp:
case Intrinsic::bitreverse:
case Intrinsic::bswap:
case Intrinsic::sadd_sat:
case Intrinsic::ssub_sat:
case Intrinsic::sshl_sat:
case Intrinsic::uadd_sat:
case Intrinsic::usub_sat:
case Intrinsic::ushl_sat:
case Intrinsic::smul_fix:
case Intrinsic::smul_fix_sat:
case Intrinsic::canonicalize:
case Intrinsic::sqrt:
Copy link
Member

@dtcxzyw dtcxzyw Jul 3, 2025

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Suggested change
case Intrinsic::sqrt:
case Intrinsic::sqrt:
case Intrinsic::frexp:

See

llvm-project/llvm/lib/Analysis/ConstantFolding.cpp

Lines 3915 to 3916 in 438863a

if (isa<PoisonValue>(Op))
return {Op, PoisonValue::get(IntTy)};

Copy link
Contributor Author

@nikic nikic Jul 3, 2025

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Consolidating the frexp case is more complicated due to the struct return. I think it needs some refactorings to ConstantFoldStructCall first.

return true;
default:
return false;
}
}

bool llvm::propagatesPoison(const Use &PoisonOp) {
const Operator *I = cast<Operator>(PoisonOp.getUser());
switch (I->getOpcode()) {
Expand All @@ -7889,38 +7930,8 @@ bool llvm::propagatesPoison(const Use &PoisonOp) {
case Instruction::Select:
return PoisonOp.getOperandNo() == 0;
case Instruction::Call:
if (auto *II = dyn_cast<IntrinsicInst>(I)) {
switch (II->getIntrinsicID()) {
// TODO: Add more intrinsics.
case Intrinsic::sadd_with_overflow:
case Intrinsic::ssub_with_overflow:
case Intrinsic::smul_with_overflow:
case Intrinsic::uadd_with_overflow:
case Intrinsic::usub_with_overflow:
case Intrinsic::umul_with_overflow:
// If an input is a vector containing a poison element, the
// two output vectors (calculated results, overflow bits)'
// corresponding lanes are poison.
return true;
case Intrinsic::ctpop:
case Intrinsic::ctlz:
case Intrinsic::cttz:
case Intrinsic::abs:
case Intrinsic::smax:
case Intrinsic::smin:
case Intrinsic::umax:
case Intrinsic::umin:
case Intrinsic::bitreverse:
case Intrinsic::bswap:
case Intrinsic::sadd_sat:
case Intrinsic::ssub_sat:
case Intrinsic::sshl_sat:
case Intrinsic::uadd_sat:
case Intrinsic::usub_sat:
case Intrinsic::ushl_sat:
return true;
}
}
if (auto *II = dyn_cast<IntrinsicInst>(I))
return intrinsicPropagatesPoison(II->getIntrinsicID());
return false;
case Instruction::ICmp:
case Instruction::FCmp:
Expand Down
8 changes: 8 additions & 0 deletions llvm/test/Transforms/InstSimplify/fold-intrinsics.ll
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -44,3 +44,11 @@ define void @powi_i16(float %V, ptr%P) {

ret void
}

define i32 @test_ctpop_poison(i32 %a) {
; CHECK-LABEL: @test_ctpop_poison(
; CHECK-NEXT: ret i32 poison
;
%res = tail call i32 @llvm.ctpop.i32(i32 poison)
ret i32 %res
}
2 changes: 1 addition & 1 deletion llvm/unittests/Analysis/ValueTrackingTest.cpp
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -910,7 +910,7 @@ TEST(ValueTracking, propagatesPoison) {
{false, "call i32 @llvm.fshr.i32(i32 %x, i32 %y, i32 %shamt)", 0},
{false, "call i32 @llvm.fshr.i32(i32 %x, i32 %y, i32 %shamt)", 1},
{false, "call i32 @llvm.fshr.i32(i32 %x, i32 %y, i32 %shamt)", 2},
{false, "call float @llvm.sqrt.f32(float %fx)", 0},
{true, "call float @llvm.sqrt.f32(float %fx)", 0},
{false, "call float @llvm.powi.f32.i32(float %fx, i32 %x)", 0},
{false, "call float @llvm.sin.f32(float %fx)", 0},
{false, "call float @llvm.cos.f32(float %fx)", 0},
Expand Down
Loading