[llvm] [InstSimplify] Fold `X * C >= X` to `true` (PR #129352)
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Fri Feb 28 19:52:56 PST 2025
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-llvm-analysis
@llvm/pr-subscribers-llvm-transforms
Author: Veera (veera-sivarajan)
<details>
<summary>Changes</summary>
Proof: https://alive2.llvm.org/ce/z/T_ocLy
Discovered in: https://github.com/rust-lang/rust/issues/114386
This PR 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
---
Full diff: https://github.com/llvm/llvm-project/pull/129352.diff
2 Files Affected:
- (modified) llvm/lib/Analysis/InstructionSimplify.cpp (+24-13)
- (modified) llvm/test/Transforms/InstSimplify/icmp-monotonic.ll (+129)
``````````diff
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
+}
``````````
</details>
https://github.com/llvm/llvm-project/pull/129352
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