[llvm-branch-commits] [llvm] 1d5d125 - [ConstantFolding] Consolidate poison propagation for intrinsics (#146878)
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Sun Jul 6 19:11:21 PDT 2025
Author: Nikita Popov
Date: 2025-07-04T09:16:28+02:00
New Revision: 1d5d1256487c1574e5a8addcf27983fd569966e5
URL: https://github.com/llvm/llvm-project/commit/1d5d1256487c1574e5a8addcf27983fd569966e5
DIFF: https://github.com/llvm/llvm-project/commit/1d5d1256487c1574e5a8addcf27983fd569966e5.diff
LOG: [ConstantFolding] Consolidate poison propagation for intrinsics (#146878)
This consolidates the "fold poison arg to poison result" constant
folding logic for intrinsics, based on a common
intrinsicPropagatesPoison() helper, which is also used for poison
propagation reasoning in ValueTracking. This ensures that the set of
supported intrinsics is consistent.
This add ucmp, scmp, smul.fix, smul.fix.sat, canonicalize and sqrt to
the intrinsicPropagatesPoison list, as these were handled by
ConstantFolding but not ValueTracking. The ctpop test is an example of
the converse, where it was handled by ValueTracking but not
ConstantFolding.
Added:
Modified:
llvm/include/llvm/Analysis/ValueTracking.h
llvm/lib/Analysis/ConstantFolding.cpp
llvm/lib/Analysis/ValueTracking.cpp
llvm/test/Transforms/InstSimplify/fold-intrinsics.ll
llvm/unittests/Analysis/ValueTrackingTest.cpp
Removed:
################################################################################
diff --git a/llvm/include/llvm/Analysis/ValueTracking.h b/llvm/include/llvm/Analysis/ValueTracking.h
index 17c79790a69f2..02990a3cb44f7 100644
--- a/llvm/include/llvm/Analysis/ValueTracking.h
+++ b/llvm/include/llvm/Analysis/ValueTracking.h
@@ -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.
diff --git a/llvm/lib/Analysis/ConstantFolding.cpp b/llvm/lib/Analysis/ConstantFolding.cpp
index 9e3c271f7d93f..af955f202ac28 100644
--- a/llvm/lib/Analysis/ConstantFolding.cpp
+++ b/llvm/lib/Analysis/ConstantFolding.cpp
@@ -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.
@@ -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)
@@ -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);
@@ -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)
@@ -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)
@@ -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))
@@ -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, IsaPred<PoisonValue>) &&
+ intrinsicPropagatesPoison(IntrinsicID))
+ return PoisonValue::get(Ty);
+
if (Operands.size() == 1)
return ConstantFoldScalarCall1(Name, IntrinsicID, Ty, Operands, TLI, Call);
diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index e576f4899810a..2b7b1ee273992 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -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:
+ return true;
+ default:
+ return false;
+ }
+}
+
bool llvm::propagatesPoison(const Use &PoisonOp) {
const Operator *I = cast<Operator>(PoisonOp.getUser());
switch (I->getOpcode()) {
@@ -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:
diff --git a/llvm/test/Transforms/InstSimplify/fold-intrinsics.ll b/llvm/test/Transforms/InstSimplify/fold-intrinsics.ll
index e45aa3fd09ce0..b66d0c76d5ede 100644
--- a/llvm/test/Transforms/InstSimplify/fold-intrinsics.ll
+++ b/llvm/test/Transforms/InstSimplify/fold-intrinsics.ll
@@ -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
+}
diff --git a/llvm/unittests/Analysis/ValueTrackingTest.cpp b/llvm/unittests/Analysis/ValueTrackingTest.cpp
index 129052fbe08b8..e283591843748 100644
--- a/llvm/unittests/Analysis/ValueTrackingTest.cpp
+++ b/llvm/unittests/Analysis/ValueTrackingTest.cpp
@@ -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},
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