[llvm] [InstCombine] Fold icmp with clamp into unsigned bound check (PR #161303)
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Mon Sep 29 18:01:23 PDT 2025
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-llvm-transforms
Author: Brandon (brandonxin)
<details>
<summary>Changes</summary>
Fix #<!-- -->157315
alive2: https://alive2.llvm.org/ce/z/v5CfSq
The equality comparison of `min(max(X, Lo), Hi)` and `X` is actually a range check on `X`. This PR folds this into an unsigned bound check `(X - Lo) u< (Hi - Lo + 1)`.
---
Full diff: https://github.com/llvm/llvm-project/pull/161303.diff
3 Files Affected:
- (modified) llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp (+46-1)
- (modified) llvm/lib/Transforms/InstCombine/InstCombineInternal.h (+1)
- (added) llvm/test/Transforms/InstCombine/icmp-clamp.ll (+295)
``````````diff
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
index e4cb457499ef5..18bf3903715d5 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -5780,6 +5780,47 @@ Instruction *InstCombinerImpl::foldICmpWithMinMax(Instruction &I,
return nullptr;
}
+// Transform patterns like:
+// icmp eq/ne X, min(max(X, Lo), Hi)
+// Into:
+// (X - Lo) u< (Hi - Lo + 1)
+Instruction *InstCombinerImpl::foldICmpWithClamp(ICmpInst &I, Value *X,
+ MinMaxIntrinsic *Min) {
+ if (!I.isEquality() || !Min->hasOneUse())
+ return nullptr;
+
+ const APInt *Lo = nullptr, *Hi = nullptr;
+ if (Min->isSigned()) {
+ if (!match(Min->getLHS(), m_OneUse(m_SMax(m_Specific(X), m_APInt(Lo)))) ||
+ !match(Min->getRHS(), m_APInt(Hi)) || !Lo->slt(*Hi))
+ return nullptr;
+ } else {
+ if (!match(Min->getLHS(), m_OneUse(m_UMax(m_Specific(X), m_APInt(Lo)))) ||
+ !match(Min->getRHS(), m_APInt(Hi)) || !Lo->ult(*Hi))
+ return nullptr;
+ }
+
+ // If Hi is the maximum value, the min operation becomes redundant and
+ // will be removed by other optimizations.
+ if ((Min->isSigned() && (Lo->isMinSignedValue() || Hi->isMaxSignedValue())) ||
+ (!Min->isSigned() && (Lo->isMinValue() || Hi->isMaxValue())))
+ return nullptr;
+
+ ConstantRange CR(*Lo, *Hi + 1);
+ ICmpInst::Predicate Pred;
+ APInt C, Offset;
+ if (I.getPredicate() == ICmpInst::ICMP_EQ)
+ CR.getEquivalentICmp(Pred, C, Offset);
+ else
+ CR.inverse().getEquivalentICmp(Pred, C, Offset);
+
+ if (Offset != 0)
+ X = Builder.CreateAdd(X, ConstantInt::get(X->getType(), Offset));
+
+ return replaceInstUsesWith(
+ I, Builder.CreateICmp(Pred, X, ConstantInt::get(X->getType(), C)));
+}
+
// Canonicalize checking for a power-of-2-or-zero value:
static Instruction *foldICmpPow2Test(ICmpInst &I,
InstCombiner::BuilderTy &Builder) {
@@ -7467,10 +7508,14 @@ Instruction *InstCombinerImpl::foldICmpCommutative(CmpPredicate Pred,
if (Instruction *NI = foldSelectICmp(Pred, SI, Op1, CxtI))
return NI;
- if (auto *MinMax = dyn_cast<MinMaxIntrinsic>(Op0))
+ if (auto *MinMax = dyn_cast<MinMaxIntrinsic>(Op0)) {
if (Instruction *Res = foldICmpWithMinMax(CxtI, MinMax, Op1, Pred))
return Res;
+ if (Instruction *Res = foldICmpWithClamp(CxtI, Op1, MinMax))
+ return Res;
+ }
+
{
Value *X;
const APInt *C;
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineInternal.h b/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
index 4f94aa2d38541..e01c145bf5de3 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
+++ b/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
@@ -725,6 +725,7 @@ class LLVM_LIBRARY_VISIBILITY InstCombinerImpl final
Instruction *foldICmpBinOp(ICmpInst &Cmp, const SimplifyQuery &SQ);
Instruction *foldICmpWithMinMax(Instruction &I, MinMaxIntrinsic *MinMax,
Value *Z, CmpPredicate Pred);
+ Instruction *foldICmpWithClamp(ICmpInst &Cmp, Value *X, MinMaxIntrinsic *Min);
Instruction *foldICmpEquality(ICmpInst &Cmp);
Instruction *foldIRemByPowerOfTwoToBitTest(ICmpInst &I);
Instruction *foldSignBitTest(ICmpInst &I);
diff --git a/llvm/test/Transforms/InstCombine/icmp-clamp.ll b/llvm/test/Transforms/InstCombine/icmp-clamp.ll
new file mode 100644
index 0000000000000..4866dbffb567a
--- /dev/null
+++ b/llvm/test/Transforms/InstCombine/icmp-clamp.ll
@@ -0,0 +1,295 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 6
+; RUN: opt < %s -passes=instcombine -S | FileCheck %s
+
+declare void @use(i32)
+
+define i1 @test_i32_eq(i32 %x) {
+; CHECK-LABEL: define i1 @test_i32_eq(
+; CHECK-SAME: i32 [[X:%.*]]) {
+; CHECK-NEXT: [[TMP1:%.*]] = add i32 [[X]], 95
+; CHECK-NEXT: [[CMP:%.*]] = icmp ult i32 [[TMP1]], 256
+; CHECK-NEXT: ret i1 [[CMP]]
+;
+ %v1 = tail call i32 @llvm.smax.i32(i32 %x, i32 -95)
+ %v2 = tail call i32 @llvm.smin.i32(i32 %v1, i32 160)
+ %cmp = icmp eq i32 %v2, %x
+ ret i1 %cmp
+}
+
+define i1 @test_i32_ne(i32 %x) {
+; CHECK-LABEL: define i1 @test_i32_ne(
+; CHECK-SAME: i32 [[X:%.*]]) {
+; CHECK-NEXT: [[TMP1:%.*]] = add i32 [[X]], -161
+; CHECK-NEXT: [[CMP:%.*]] = icmp ult i32 [[TMP1]], -256
+; CHECK-NEXT: ret i1 [[CMP]]
+;
+ %v1 = tail call i32 @llvm.smax.i32(i32 %x, i32 -95)
+ %v2 = tail call i32 @llvm.smin.i32(i32 %v1, i32 160)
+ %cmp = icmp ne i32 %v2, %x
+ ret i1 %cmp
+}
+
+define i1 @test_i32_eq_no_add(i32 %x) {
+; CHECK-LABEL: define i1 @test_i32_eq_no_add(
+; CHECK-SAME: i32 [[X:%.*]]) {
+; CHECK-NEXT: [[CMP:%.*]] = icmp ult i32 [[X]], 161
+; CHECK-NEXT: ret i1 [[CMP]]
+;
+ %v1 = tail call i32 @llvm.smax.i32(i32 %x, i32 0)
+ %v2 = tail call i32 @llvm.smin.i32(i32 %v1, i32 160)
+ %cmp = icmp eq i32 %v2, %x
+ ret i1 %cmp
+}
+
+define i1 @test_i32_ne_no_add(i32 %x) {
+; CHECK-LABEL: define i1 @test_i32_ne_no_add(
+; CHECK-SAME: i32 [[X:%.*]]) {
+; CHECK-NEXT: [[CMP:%.*]] = icmp ugt i32 [[X]], 160
+; CHECK-NEXT: ret i1 [[CMP]]
+;
+ %v1 = tail call i32 @llvm.smax.i32(i32 %x, i32 0)
+ %v2 = tail call i32 @llvm.smin.i32(i32 %v1, i32 160)
+ %cmp = icmp ne i32 %v2, %x
+ ret i1 %cmp
+}
+
+define i1 @test_unsigned_eq(i32 %x) {
+; CHECK-LABEL: define i1 @test_unsigned_eq(
+; CHECK-SAME: i32 [[X:%.*]]) {
+; CHECK-NEXT: [[TMP1:%.*]] = add i32 [[X]], -10
+; CHECK-NEXT: [[CMP:%.*]] = icmp ult i32 [[TMP1]], 91
+; CHECK-NEXT: ret i1 [[CMP]]
+;
+ %v1 = tail call i32 @llvm.umax.i32(i32 %x, i32 10)
+ %v2 = tail call i32 @llvm.umin.i32(i32 %v1, i32 100)
+ %cmp = icmp eq i32 %v2, %x
+ ret i1 %cmp
+}
+
+define i1 @test_unsigned_ne(i32 %x) {
+; CHECK-LABEL: define i1 @test_unsigned_ne(
+; CHECK-SAME: i32 [[X:%.*]]) {
+; CHECK-NEXT: [[TMP1:%.*]] = add i32 [[X]], -101
+; CHECK-NEXT: [[CMP:%.*]] = icmp ult i32 [[TMP1]], -91
+; CHECK-NEXT: ret i1 [[CMP]]
+;
+ %v1 = tail call i32 @llvm.umax.i32(i32 %x, i32 10)
+ %v2 = tail call i32 @llvm.umin.i32(i32 %v1, i32 100)
+ %cmp = icmp ne i32 %v2, %x
+ ret i1 %cmp
+}
+
+
+; Different bit widths
+define i1 @test_i8_eq(i8 %x) {
+; CHECK-LABEL: define i1 @test_i8_eq(
+; CHECK-SAME: i8 [[X:%.*]]) {
+; CHECK-NEXT: [[TMP1:%.*]] = add i8 [[X]], 50
+; CHECK-NEXT: [[CMP:%.*]] = icmp ult i8 [[TMP1]], 101
+; CHECK-NEXT: ret i1 [[CMP]]
+;
+ %v1 = tail call i8 @llvm.smax.i8(i8 %x, i8 -50)
+ %v2 = tail call i8 @llvm.smin.i8(i8 %v1, i8 50)
+ %cmp = icmp eq i8 %v2, %x
+ ret i1 %cmp
+}
+
+define i1 @test_i16_eq(i16 %x) {
+; CHECK-LABEL: define i1 @test_i16_eq(
+; CHECK-SAME: i16 [[X:%.*]]) {
+; CHECK-NEXT: [[TMP1:%.*]] = add i16 [[X]], 1000
+; CHECK-NEXT: [[CMP:%.*]] = icmp ult i16 [[TMP1]], 2001
+; CHECK-NEXT: ret i1 [[CMP]]
+;
+ %v1 = tail call i16 @llvm.smax.i16(i16 %x, i16 -1000)
+ %v2 = tail call i16 @llvm.smin.i16(i16 %v1, i16 1000)
+ %cmp = icmp eq i16 %v2, %x
+ ret i1 %cmp
+}
+
+define i1 @test_i64_eq(i64 %x) {
+; CHECK-LABEL: define i1 @test_i64_eq(
+; CHECK-SAME: i64 [[X:%.*]]) {
+; CHECK-NEXT: [[TMP1:%.*]] = add i64 [[X]], 1
+; CHECK-NEXT: [[CMP:%.*]] = icmp sgt i64 [[TMP1]], -1
+; CHECK-NEXT: ret i1 [[CMP]]
+;
+ %v1 = tail call i64 @llvm.smax.i64(i64 %x, i64 -1)
+ %v2 = tail call i64 @llvm.smin.i64(i64 %v1, i64 9223372036854775806)
+ %cmp = icmp eq i64 %v2, %x
+ ret i1 %cmp
+}
+
+; Negative tests - wrong predicate
+define i1 @test_wrong_pred_slt(i32 %x) {
+; CHECK-LABEL: define i1 @test_wrong_pred_slt(
+; CHECK-SAME: i32 [[X:%.*]]) {
+; CHECK-NEXT: [[CMP:%.*]] = icmp sgt i32 [[X]], 160
+; CHECK-NEXT: ret i1 [[CMP]]
+;
+ %v1 = tail call i32 @llvm.smax.i32(i32 %x, i32 -95)
+ %v2 = tail call i32 @llvm.smin.i32(i32 %v1, i32 160)
+ %cmp = icmp slt i32 %v2, %x
+ ret i1 %cmp
+}
+
+
+; Negative tests - not a clamp pattern
+define i1 @test_not_clamp_pattern(i32 %x, i32 %y) {
+; CHECK-LABEL: define i1 @test_not_clamp_pattern(
+; CHECK-SAME: i32 [[X:%.*]], i32 [[Y:%.*]]) {
+; CHECK-NEXT: [[V1:%.*]] = tail call i32 @llvm.smax.i32(i32 [[Y]], i32 -95)
+; CHECK-NEXT: [[V2:%.*]] = tail call i32 @llvm.smin.i32(i32 [[V1]], i32 160)
+; CHECK-NEXT: [[CMP:%.*]] = icmp eq i32 [[V2]], [[X]]
+; CHECK-NEXT: ret i1 [[CMP]]
+;
+ %v1 = tail call i32 @llvm.smax.i32(i32 %y, i32 -95)
+ %v2 = tail call i32 @llvm.smin.i32(i32 %v1, i32 160)
+ %cmp = icmp eq i32 %v2, %x
+ ret i1 %cmp
+}
+
+; Negative tests - Lo >= Hi
+define i1 @test_invalid_range(i32 %x) {
+; CHECK-LABEL: define i1 @test_invalid_range(
+; CHECK-SAME: i32 [[X:%.*]]) {
+; CHECK-NEXT: [[CMP:%.*]] = icmp eq i32 [[X]], 50
+; CHECK-NEXT: ret i1 [[CMP]]
+;
+ %v1 = tail call i32 @llvm.smax.i32(i32 %x, i32 100)
+ %v2 = tail call i32 @llvm.smin.i32(i32 %v1, i32 50)
+ %cmp = icmp eq i32 %v2, %x
+ ret i1 %cmp
+}
+
+; Negative tests - Lo is minimum signed value
+define i1 @test_lo_min_signed(i32 %x) {
+; CHECK-LABEL: define i1 @test_lo_min_signed(
+; CHECK-SAME: i32 [[X:%.*]]) {
+; CHECK-NEXT: [[CMP:%.*]] = icmp slt i32 [[X]], 161
+; CHECK-NEXT: ret i1 [[CMP]]
+;
+ %v1 = tail call i32 @llvm.smax.i32(i32 %x, i32 -2147483648)
+ %v2 = tail call i32 @llvm.smin.i32(i32 %v1, i32 160)
+ %cmp = icmp eq i32 %v2, %x
+ ret i1 %cmp
+}
+
+; Negative tests - Hi is maximum signed value
+define i1 @test_hi_max_signed(i32 %x) {
+; CHECK-LABEL: define i1 @test_hi_max_signed(
+; CHECK-SAME: i32 [[X:%.*]]) {
+; CHECK-NEXT: [[CMP:%.*]] = icmp sgt i32 [[X]], -96
+; CHECK-NEXT: ret i1 [[CMP]]
+;
+ %v1 = tail call i32 @llvm.smax.i32(i32 %x, i32 -95)
+ %v2 = tail call i32 @llvm.smin.i32(i32 %v1, i32 2147483647)
+ %cmp = icmp eq i32 %v2, %x
+ ret i1 %cmp
+}
+
+; Negative tests - Hi is maximum unsigned value
+define i1 @test_hi_max_unsigned(i32 %x) {
+; CHECK-LABEL: define i1 @test_hi_max_unsigned(
+; CHECK-SAME: i32 [[X:%.*]]) {
+; CHECK-NEXT: [[CMP:%.*]] = icmp ugt i32 [[X]], 9
+; CHECK-NEXT: ret i1 [[CMP]]
+;
+ %v1 = tail call i32 @llvm.umax.i32(i32 %x, i32 10)
+ %v2 = tail call i32 @llvm.umin.i32(i32 %v1, i32 4294967295)
+ %cmp = icmp eq i32 %v2, %x
+ ret i1 %cmp
+}
+
+; Multi-use tests - multiple uses of max
+define i1 @test_multi_use_max(i32 %x) {
+; CHECK-LABEL: define i1 @test_multi_use_max(
+; CHECK-SAME: i32 [[X:%.*]]) {
+; CHECK-NEXT: [[V1:%.*]] = tail call i32 @llvm.smax.i32(i32 [[X]], i32 -95)
+; CHECK-NEXT: call void @use(i32 [[V1]])
+; CHECK-NEXT: [[V2:%.*]] = tail call i32 @llvm.smin.i32(i32 [[V1]], i32 160)
+; CHECK-NEXT: [[CMP:%.*]] = icmp eq i32 [[V2]], [[X]]
+; CHECK-NEXT: ret i1 [[CMP]]
+;
+ %v1 = tail call i32 @llvm.smax.i32(i32 %x, i32 -95)
+ call void @use(i32 %v1)
+ %v2 = tail call i32 @llvm.smin.i32(i32 %v1, i32 160)
+ %cmp = icmp eq i32 %v2, %x
+ ret i1 %cmp
+}
+
+; Multi-use tests - multiple uses of min
+define i1 @test_multi_use_min(i32 %x) {
+; CHECK-LABEL: define i1 @test_multi_use_min(
+; CHECK-SAME: i32 [[X:%.*]]) {
+; CHECK-NEXT: [[V1:%.*]] = tail call i32 @llvm.smax.i32(i32 [[X]], i32 -95)
+; CHECK-NEXT: [[V2:%.*]] = tail call i32 @llvm.smin.i32(i32 [[V1]], i32 160)
+; CHECK-NEXT: call void @use(i32 [[V2]])
+; CHECK-NEXT: [[CMP:%.*]] = icmp eq i32 [[V2]], [[X]]
+; CHECK-NEXT: ret i1 [[CMP]]
+;
+ %v1 = tail call i32 @llvm.smax.i32(i32 %x, i32 -95)
+ %v2 = tail call i32 @llvm.smin.i32(i32 %v1, i32 160)
+ call void @use(i32 %v2)
+ %cmp = icmp eq i32 %v2, %x
+ ret i1 %cmp
+}
+
+; Commuted tests
+define i1 @test_commuted_eq(i32 %x) {
+; CHECK-LABEL: define i1 @test_commuted_eq(
+; CHECK-SAME: i32 [[X:%.*]]) {
+; CHECK-NEXT: [[TMP1:%.*]] = add i32 [[X]], 95
+; CHECK-NEXT: [[CMP:%.*]] = icmp ult i32 [[TMP1]], 256
+; CHECK-NEXT: ret i1 [[CMP]]
+;
+ %v1 = tail call i32 @llvm.smax.i32(i32 %x, i32 -95)
+ %v2 = tail call i32 @llvm.smin.i32(i32 %v1, i32 160)
+ %cmp = icmp eq i32 %x, %v2
+ ret i1 %cmp
+}
+
+
+; Vector tests - splat constants
+define <2 x i1> @test_vec_splat_eq(<2 x i32> %x) {
+; CHECK-LABEL: define <2 x i1> @test_vec_splat_eq(
+; CHECK-SAME: <2 x i32> [[X:%.*]]) {
+; CHECK-NEXT: [[TMP1:%.*]] = add <2 x i32> [[X]], splat (i32 50)
+; CHECK-NEXT: [[CMP:%.*]] = icmp ult <2 x i32> [[TMP1]], splat (i32 101)
+; CHECK-NEXT: ret <2 x i1> [[CMP]]
+;
+ %v1 = tail call <2 x i32> @llvm.smax.v2i32(<2 x i32> %x, <2 x i32> <i32 -50, i32 -50>)
+ %v2 = tail call <2 x i32> @llvm.smin.v2i32(<2 x i32> %v1, <2 x i32> <i32 50, i32 50>)
+ %cmp = icmp eq <2 x i32> %v2, %x
+ ret <2 x i1> %cmp
+}
+
+; Vector tests - poison elements
+define <2 x i1> @test_vec_poison_eq(<2 x i32> %x) {
+; CHECK-LABEL: define <2 x i1> @test_vec_poison_eq(
+; CHECK-SAME: <2 x i32> [[X:%.*]]) {
+; CHECK-NEXT: [[V1:%.*]] = tail call <2 x i32> @llvm.smax.v2i32(<2 x i32> [[X]], <2 x i32> <i32 -50, i32 poison>)
+; CHECK-NEXT: [[V2:%.*]] = tail call <2 x i32> @llvm.smin.v2i32(<2 x i32> [[V1]], <2 x i32> <i32 50, i32 poison>)
+; CHECK-NEXT: [[CMP:%.*]] = icmp eq <2 x i32> [[V2]], [[X]]
+; CHECK-NEXT: ret <2 x i1> [[CMP]]
+;
+ %v1 = tail call <2 x i32> @llvm.smax.v2i32(<2 x i32> %x, <2 x i32> <i32 -50, i32 poison>)
+ %v2 = tail call <2 x i32> @llvm.smin.v2i32(<2 x i32> %v1, <2 x i32> <i32 50, i32 poison>)
+ %cmp = icmp eq <2 x i32> %v2, %x
+ ret <2 x i1> %cmp
+}
+
+; Vector tests - non-splat
+define <2 x i1> @test_vec_non_splat_eq(<2 x i32> %x) {
+; CHECK-LABEL: define <2 x i1> @test_vec_non_splat_eq(
+; CHECK-SAME: <2 x i32> [[X:%.*]]) {
+; CHECK-NEXT: [[V1:%.*]] = tail call <2 x i32> @llvm.smax.v2i32(<2 x i32> [[X]], <2 x i32> <i32 -50, i32 -30>)
+; CHECK-NEXT: [[V2:%.*]] = tail call <2 x i32> @llvm.smin.v2i32(<2 x i32> [[V1]], <2 x i32> <i32 50, i32 70>)
+; CHECK-NEXT: [[CMP:%.*]] = icmp eq <2 x i32> [[V2]], [[X]]
+; CHECK-NEXT: ret <2 x i1> [[CMP]]
+;
+ %v1 = tail call <2 x i32> @llvm.smax.v2i32(<2 x i32> %x, <2 x i32> <i32 -50, i32 -30>)
+ %v2 = tail call <2 x i32> @llvm.smin.v2i32(<2 x i32> %v1, <2 x i32> <i32 50, i32 70>)
+ %cmp = icmp eq <2 x i32> %v2, %x
+ ret <2 x i1> %cmp
+}
``````````
</details>
https://github.com/llvm/llvm-project/pull/161303
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