[InstSimplify] Fold X * C >= X to true
#129352
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@llvm/pr-subscribers-llvm-analysis @llvm/pr-subscribers-llvm-transforms Author: Veera (veera-sivarajan) ChangesProof: https://alive2.llvm.org/ce/z/T_ocLy Discovered in: rust-lang/rust#114386 This PR folds Folds for other math operators exist already: https://llvm-ir.godbolt.org/z/GKcYEf5Kb Full diff: https://github.com/llvm/llvm-project/pull/129352.diff 2 Files Affected:
diff --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
index 59002cd934ab1..2db1572f55a27 100644
--- a/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -3031,7 +3031,9 @@ enum class MonotonicType { GreaterEq, LowerEq };
/// Get values V_i such that V uge V_i (GreaterEq) or V ule V_i (LowerEq).
static void getUnsignedMonotonicValues(SmallPtrSetImpl<Value *> &Res, Value *V,
- MonotonicType Type, unsigned Depth = 0) {
+ MonotonicType Type,
+ const SimplifyQuery &Q,
+ unsigned Depth = 0) {
if (!Res.insert(V).second)
return;
@@ -3047,24 +3049,31 @@ static void getUnsignedMonotonicValues(SmallPtrSetImpl<Value *> &Res, Value *V,
if (Type == MonotonicType::GreaterEq) {
if (match(I, m_Or(m_Value(X), m_Value(Y))) ||
match(I, m_Intrinsic<Intrinsic::uadd_sat>(m_Value(X), m_Value(Y)))) {
- getUnsignedMonotonicValues(Res, X, Type, Depth);
- getUnsignedMonotonicValues(Res, Y, Type, Depth);
+ getUnsignedMonotonicValues(Res, X, Type, Q, Depth);
+ getUnsignedMonotonicValues(Res, Y, Type, Q, Depth);
+ }
+ // X * Y >= X --> true
+ if (match(I, m_NUWMul(m_Value(X), m_Value(Y)))) {
+ if (isKnownNonZero(X, Q))
+ getUnsignedMonotonicValues(Res, Y, Type, Q, Depth);
+ if (isKnownNonZero(Y, Q))
+ getUnsignedMonotonicValues(Res, X, Type, Q, Depth);
}
} else {
assert(Type == MonotonicType::LowerEq);
switch (I->getOpcode()) {
case Instruction::And:
- getUnsignedMonotonicValues(Res, I->getOperand(0), Type, Depth);
- getUnsignedMonotonicValues(Res, I->getOperand(1), Type, Depth);
+ getUnsignedMonotonicValues(Res, I->getOperand(0), Type, Q, Depth);
+ getUnsignedMonotonicValues(Res, I->getOperand(1), Type, Q, Depth);
break;
case Instruction::URem:
case Instruction::UDiv:
case Instruction::LShr:
- getUnsignedMonotonicValues(Res, I->getOperand(0), Type, Depth);
+ getUnsignedMonotonicValues(Res, I->getOperand(0), Type, Q, Depth);
break;
case Instruction::Call:
if (match(I, m_Intrinsic<Intrinsic::usub_sat>(m_Value(X))))
- getUnsignedMonotonicValues(Res, X, Type, Depth);
+ getUnsignedMonotonicValues(Res, X, Type, Q, Depth);
break;
default:
break;
@@ -3073,16 +3082,16 @@ static void getUnsignedMonotonicValues(SmallPtrSetImpl<Value *> &Res, Value *V,
}
static Value *simplifyICmpUsingMonotonicValues(CmpPredicate Pred, Value *LHS,
- Value *RHS) {
+ Value *RHS,
+ const SimplifyQuery &Q) {
if (Pred != ICmpInst::ICMP_UGE && Pred != ICmpInst::ICMP_ULT)
return nullptr;
-
// We have LHS uge GreaterValues and LowerValues uge RHS. If any of the
// GreaterValues and LowerValues are the same, it follows that LHS uge RHS.
SmallPtrSet<Value *, 4> GreaterValues;
SmallPtrSet<Value *, 4> LowerValues;
- getUnsignedMonotonicValues(GreaterValues, LHS, MonotonicType::GreaterEq);
- getUnsignedMonotonicValues(LowerValues, RHS, MonotonicType::LowerEq);
+ getUnsignedMonotonicValues(GreaterValues, LHS, MonotonicType::GreaterEq, Q);
+ getUnsignedMonotonicValues(LowerValues, RHS, MonotonicType::LowerEq, Q);
for (Value *GV : GreaterValues)
if (LowerValues.contains(GV))
return ConstantInt::getBool(getCompareTy(LHS),
@@ -3994,14 +4003,16 @@ static Value *simplifyICmpInst(CmpPredicate Pred, Value *LHS, Value *RHS,
if (Value *V = simplifyICmpWithIntrinsicOnLHS(Pred, LHS, RHS))
return V;
+
if (Value *V = simplifyICmpWithIntrinsicOnLHS(
ICmpInst::getSwappedPredicate(Pred), RHS, LHS))
return V;
- if (Value *V = simplifyICmpUsingMonotonicValues(Pred, LHS, RHS))
+ if (Value *V = simplifyICmpUsingMonotonicValues(Pred, LHS, RHS, Q))
return V;
+
if (Value *V = simplifyICmpUsingMonotonicValues(
- ICmpInst::getSwappedPredicate(Pred), RHS, LHS))
+ ICmpInst::getSwappedPredicate(Pred), RHS, LHS, Q))
return V;
if (Value *V = simplifyICmpWithDominatingAssume(Pred, LHS, RHS, Q))
diff --git a/llvm/test/Transforms/InstSimplify/icmp-monotonic.ll b/llvm/test/Transforms/InstSimplify/icmp-monotonic.ll
index e1a4ee91bd15c..1063136ab54c4 100644
--- a/llvm/test/Transforms/InstSimplify/icmp-monotonic.ll
+++ b/llvm/test/Transforms/InstSimplify/icmp-monotonic.ll
@@ -216,3 +216,132 @@ define i1 @lshr_add_ule_non_monotonic(i32 %x, i32 %y, i32 %z) {
%cmp = icmp ule i32 %op1, %op2
ret i1 %cmp
}
+
+define i1 @mul_nuw_nonzero_rhs_monotonic(i8 %x, i8 %c) {
+; CHECK-LABEL: define i1 @mul_nuw_nonzero_rhs_monotonic(
+; CHECK-SAME: i8 [[X:%.*]], i8 [[C:%.*]]) {
+; CHECK-NEXT: [[C_NONZERO:%.*]] = icmp ne i8 [[C]], 0
+; CHECK-NEXT: call void @llvm.assume(i1 [[C_NONZERO]])
+; CHECK-NEXT: ret i1 true
+;
+ %c_nonzero = icmp ne i8 %c, 0
+ call void @llvm.assume(i1 %c_nonzero)
+
+ %prod = mul nuw i8 %x, %c
+ %cmp = icmp uge i8 %prod, %x
+ ret i1 %cmp
+}
+
+define i1 @mul_nuw_nonzero_rhs_monotonic_inverse_predicate(i8 %x, i8 %c) {
+; CHECK-LABEL: define i1 @mul_nuw_nonzero_rhs_monotonic_inverse_predicate(
+; CHECK-SAME: i8 [[X:%.*]], i8 [[C:%.*]]) {
+; CHECK-NEXT: [[C_NONZERO:%.*]] = icmp ne i8 [[C]], 0
+; CHECK-NEXT: call void @llvm.assume(i1 [[C_NONZERO]])
+; CHECK-NEXT: ret i1 false
+;
+ %c_nonzero = icmp ne i8 %c, 0
+ call void @llvm.assume(i1 %c_nonzero)
+
+ %prod = mul nuw i8 %x, %c
+ %cmp = icmp ult i8 %prod, %x
+ ret i1 %cmp
+}
+
+define i1 @mul_nuw_nonzero_lhs_monotonic(i8 %x, i8 %c) {
+; CHECK-LABEL: define i1 @mul_nuw_nonzero_lhs_monotonic(
+; CHECK-SAME: i8 [[X:%.*]], i8 [[C:%.*]]) {
+; CHECK-NEXT: [[C_NONZERO:%.*]] = icmp ne i8 [[X]], 0
+; CHECK-NEXT: call void @llvm.assume(i1 [[C_NONZERO]])
+; CHECK-NEXT: ret i1 true
+;
+ %c_nonzero = icmp ne i8 %x, 0
+ call void @llvm.assume(i1 %c_nonzero)
+
+ %prod = mul nuw i8 %x, %c
+ %cmp = icmp uge i8 %prod, %c
+ ret i1 %cmp
+}
+
+define i1 @mul_nuw_nonzero_lhs_rhs_monotonic(i8 %x, i8 %c) {
+; CHECK-LABEL: define i1 @mul_nuw_nonzero_lhs_rhs_monotonic(
+; CHECK-SAME: i8 [[X:%.*]], i8 [[C:%.*]]) {
+; CHECK-NEXT: [[C_NONZERO:%.*]] = icmp ne i8 [[C]], 0
+; CHECK-NEXT: call void @llvm.assume(i1 [[C_NONZERO]])
+; CHECK-NEXT: [[X_NONZERO:%.*]] = icmp ne i8 [[X]], 0
+; CHECK-NEXT: call void @llvm.assume(i1 [[X_NONZERO]])
+; CHECK-NEXT: ret i1 true
+;
+ %c_nonzero = icmp ne i8 %c, 0
+ call void @llvm.assume(i1 %c_nonzero)
+
+ %x_nonzero = icmp ne i8 %x, 0
+ call void @llvm.assume(i1 %x_nonzero)
+
+ %prod = mul nuw i8 %x, %c
+ %cmp = icmp uge i8 %prod, %x
+ ret i1 %cmp
+}
+
+
+define i1 @negative_mul_non_nsw(i8 %x, i8 %c) {
+; CHECK-LABEL: define i1 @negative_mul_non_nsw(
+; CHECK-SAME: i8 [[X:%.*]], i8 [[C:%.*]]) {
+; CHECK-NEXT: [[C_NONZERO:%.*]] = icmp ne i8 [[C]], 0
+; CHECK-NEXT: call void @llvm.assume(i1 [[C_NONZERO]])
+; CHECK-NEXT: [[X3:%.*]] = mul i8 [[X]], [[C]]
+; CHECK-NEXT: [[CMP:%.*]] = icmp uge i8 [[X3]], [[X]]
+; CHECK-NEXT: ret i1 [[CMP]]
+;
+ %c_nonzero = icmp ne i8 %c, 0
+ call void @llvm.assume(i1 %c_nonzero)
+
+ %prod = mul i8 %x, %c
+ %cmp = icmp uge i8 %prod, %x
+ ret i1 %cmp
+}
+
+define i1 @negative_mul_no_nonzero(i8 %x, i8 %c) {
+; CHECK-LABEL: define i1 @negative_mul_no_nonzero(
+; CHECK-SAME: i8 [[X:%.*]], i8 [[C:%.*]]) {
+; CHECK-NEXT: [[X3:%.*]] = mul nsw i8 [[X]], [[C]]
+; CHECK-NEXT: [[CMP:%.*]] = icmp uge i8 [[X3]], [[X]]
+; CHECK-NEXT: ret i1 [[CMP]]
+;
+ %prod = mul nsw i8 %x, %c
+ %cmp = icmp uge i8 %prod, %x
+ ret i1 %cmp
+}
+
+define i1 @negative_mul_lhs_maybe_zero(i8 %x, i8 %c) {
+; CHECK-LABEL: define i1 @negative_mul_lhs_maybe_zero(
+; CHECK-SAME: i8 [[X:%.*]], i8 [[C:%.*]]) {
+; CHECK-NEXT: [[C_NONZERO:%.*]] = icmp ne i8 [[C]], 0
+; CHECK-NEXT: call void @llvm.assume(i1 [[C_NONZERO]])
+; CHECK-NEXT: [[X3:%.*]] = mul nuw i8 [[X]], [[C]]
+; CHECK-NEXT: [[CMP:%.*]] = icmp uge i8 [[X3]], [[C]]
+; CHECK-NEXT: ret i1 [[CMP]]
+;
+ %c_nonzero = icmp ne i8 %c, 0
+ call void @llvm.assume(i1 %c_nonzero)
+
+ %prod = mul nuw i8 %x, %c
+ %cmp = icmp uge i8 %prod, %c
+ ret i1 %cmp
+}
+
+define i1 @negative_mul_rhs_maybe_zero(i8 %x, i8 %c) {
+; CHECK-LABEL: define i1 @negative_mul_rhs_maybe_zero(
+; CHECK-SAME: i8 [[X:%.*]], i8 [[C:%.*]]) {
+; CHECK-NEXT: [[C_NONZERO:%.*]] = icmp ne i8 [[X]], 0
+; CHECK-NEXT: call void @llvm.assume(i1 [[C_NONZERO]])
+; CHECK-NEXT: [[X3:%.*]] = mul nuw i8 [[X]], [[C]]
+; CHECK-NEXT: [[CMP:%.*]] = icmp uge i8 [[X3]], [[X]]
+; CHECK-NEXT: ret i1 [[CMP]]
+;
+ %c_nonzero = icmp ne i8 %x, 0
+ call void @llvm.assume(i1 %c_nonzero)
+
+ %prod = mul nuw i8 %x, %c
+ %cmp = icmp uge i8 %prod, %x
+ ret i1 %cmp
+}
|
This was referenced Mar 1, 2025
nikic
reviewed
Mar 1, 2025
| } | ||
| // X * Y >= X --> true | ||
| if (match(I, m_NUWMul(m_Value(X), m_Value(Y)))) { | ||
| if (isKnownNonZero(X, Q)) |
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Do we need the non-constant support?
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It is needed by assimp:
https://github.com/assimp/assimp/blob/2bce77f909b9f56c8c67cff33cc73a244505aa46/code/AssetLib/glTF2/glTF2Asset.inl#L897-L903
%switch.gep = getelementptr inbounds nuw [7 x i64], ptr @switch.table._ZN5glTF28Accessor6Sparse9PatchDataEj, i64 0, i64 %307
%switch.load = load i64, ptr %switch.gep, align 8
%308 = mul nuw nsw i64 %switch.load, %202
store i64 %308, ptr %20, align 8
%309 = icmp samesign ult i64 %308, %202
Proof: https://alive2.llvm.org/ce/z/T_ocLy This patch folds `X * C >= X` to `true` when `C` is known to be non-zero and `mul` is `nuw`. Folds for other math operators exist already: https://llvm-ir.godbolt.org/z/GKcYEf5Kb
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LLVM Buildbot has detected a new failure on builder Full details are available at: https://lab.llvm.org/buildbot/#/builders/88/builds/8627 Here is the relevant piece of the build log for the reference |
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Proof: https://alive2.llvm.org/ce/z/T_ocLy
Discovered in: rust-lang/rust#114386
This PR folds
X * C >= XtotruewhenCis known to be non-zero andmulisnuw.Folds for other math operators exist already: https://llvm-ir.godbolt.org/z/GKcYEf5Kb