[llvm] [SCCP] Simplify [us]cmp(X, Y) into X - Y (PR #144717)
Yingwei Zheng via llvm-commits
llvm-commits at lists.llvm.org
Wed Jun 18 07:53:24 PDT 2025
https://github.com/dtcxzyw created https://github.com/llvm/llvm-project/pull/144717
If the difference between [us]cmp's operands is not greater than 1, we can simplify it into `X - Y`.
Alive2: https://alive2.llvm.org/ce/z/JS55so
llvm-opt-benchmark diff: https://github.com/dtcxzyw/llvm-opt-benchmark/pull/2464/files
>From d6d8d35657b0d3a3bf18fd8cd60ea272c7372fec Mon Sep 17 00:00:00 2001
From: Yingwei Zheng <dtcxzyw2333 at gmail.com>
Date: Wed, 18 Jun 2025 22:44:25 +0800
Subject: [PATCH 1/2] [SCCP] Add pre-commit tests. NFC.
---
llvm/test/Transforms/SCCP/uscmp.ll | 76 ++++++++++++++++++++++++++++++
1 file changed, 76 insertions(+)
create mode 100644 llvm/test/Transforms/SCCP/uscmp.ll
diff --git a/llvm/test/Transforms/SCCP/uscmp.ll b/llvm/test/Transforms/SCCP/uscmp.ll
new file mode 100644
index 0000000000000..9b9974a93a009
--- /dev/null
+++ b/llvm/test/Transforms/SCCP/uscmp.ll
@@ -0,0 +1,76 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt -passes=sccp -S < %s | FileCheck %s
+
+define i32 @scmp_to_sub(i32 range(i32 -1, 2) %a) {
+; CHECK-LABEL: define i32 @scmp_to_sub(
+; CHECK-SAME: i32 range(i32 -1, 2) [[A:%.*]]) {
+; CHECK-NEXT: [[SCMP:%.*]] = call i32 @llvm.scmp.i32.i32(i32 [[A]], i32 0)
+; CHECK-NEXT: ret i32 [[SCMP]]
+;
+ %scmp = call i32 @llvm.scmp(i32 %a, i32 0)
+ ret i32 %scmp
+}
+
+define i32 @scmp_zext_to_sub(i1 %a, i1 %b) {
+; CHECK-LABEL: define i32 @scmp_zext_to_sub(
+; CHECK-SAME: i1 [[A:%.*]], i1 [[B:%.*]]) {
+; CHECK-NEXT: [[ZEXT_A:%.*]] = zext i1 [[A]] to i32
+; CHECK-NEXT: [[ZEXT_B:%.*]] = zext i1 [[B]] to i32
+; CHECK-NEXT: [[SCMP:%.*]] = call i32 @llvm.scmp.i32.i32(i32 [[ZEXT_A]], i32 [[ZEXT_B]])
+; CHECK-NEXT: ret i32 [[SCMP]]
+;
+ %zext_a = zext i1 %a to i32
+ %zext_b = zext i1 %b to i32
+ %scmp = call i32 @llvm.scmp(i32 %zext_a, i32 %zext_b)
+ ret i32 %scmp
+}
+
+define i8 @scmp_to_sub_trunc(i32 range(i32 -1, 2) %a) {
+; CHECK-LABEL: define i8 @scmp_to_sub_trunc(
+; CHECK-SAME: i32 range(i32 -1, 2) [[A:%.*]]) {
+; CHECK-NEXT: [[SCMP:%.*]] = call i8 @llvm.scmp.i8.i32(i32 [[A]], i32 0)
+; CHECK-NEXT: ret i8 [[SCMP]]
+;
+ %scmp = call i8 @llvm.scmp(i32 %a, i32 0)
+ ret i8 %scmp
+}
+
+define i64 @scmp_to_sub_sext(i32 range(i32 -1, 2) %a) {
+; CHECK-LABEL: define i64 @scmp_to_sub_sext(
+; CHECK-SAME: i32 range(i32 -1, 2) [[A:%.*]]) {
+; CHECK-NEXT: [[SCMP:%.*]] = call i64 @llvm.scmp.i64.i32(i32 [[A]], i32 0)
+; CHECK-NEXT: ret i64 [[SCMP]]
+;
+ %scmp = call i64 @llvm.scmp(i32 %a, i32 0)
+ ret i64 %scmp
+}
+
+define i32 @scmp_to_sub_small_range(i32 range(i32 -1, 1) %a) {
+; CHECK-LABEL: define i32 @scmp_to_sub_small_range(
+; CHECK-SAME: i32 range(i32 -1, 1) [[A:%.*]]) {
+; CHECK-NEXT: [[SCMP:%.*]] = call i32 @llvm.scmp.i32.i32(i32 [[A]], i32 0)
+; CHECK-NEXT: ret i32 [[SCMP]]
+;
+ %scmp = call i32 @llvm.scmp(i32 %a, i32 0)
+ ret i32 %scmp
+}
+
+define i32 @ucmp_to_sub(i32 range(i32 0, 3) %a) {
+; CHECK-LABEL: define i32 @ucmp_to_sub(
+; CHECK-SAME: i32 range(i32 0, 3) [[A:%.*]]) {
+; CHECK-NEXT: [[SCMP:%.*]] = call i32 @llvm.scmp.i32.i32(i32 [[A]], i32 1)
+; CHECK-NEXT: ret i32 [[SCMP]]
+;
+ %scmp = call i32 @llvm.scmp(i32 %a, i32 1)
+ ret i32 %scmp
+}
+
+define i32 @scmp_to_sub_large_range(i32 range(i32 -1, 3) %a) {
+; CHECK-LABEL: define i32 @scmp_to_sub_large_range(
+; CHECK-SAME: i32 range(i32 -1, 3) [[A:%.*]]) {
+; CHECK-NEXT: [[SCMP:%.*]] = call i32 @llvm.scmp.i32.i32(i32 [[A]], i32 0)
+; CHECK-NEXT: ret i32 [[SCMP]]
+;
+ %scmp = call i32 @llvm.scmp(i32 %a, i32 0)
+ ret i32 %scmp
+}
>From 79e351d39ef4313e32adce40a1304a5d90361e58 Mon Sep 17 00:00:00 2001
From: Yingwei Zheng <dtcxzyw2333 at gmail.com>
Date: Wed, 18 Jun 2025 22:45:17 +0800
Subject: [PATCH 2/2] [SCCP] Simplify [us]cmp(X, Y) into X - Y
---
llvm/lib/Transforms/Utils/SCCPSolver.cpp | 37 +++++++++++++++++++++++-
llvm/test/Transforms/SCCP/uscmp.ll | 14 +++++----
2 files changed, 44 insertions(+), 7 deletions(-)
diff --git a/llvm/lib/Transforms/Utils/SCCPSolver.cpp b/llvm/lib/Transforms/Utils/SCCPSolver.cpp
index f4b378b82daec..0e3f0647d6284 100644
--- a/llvm/lib/Transforms/Utils/SCCPSolver.cpp
+++ b/llvm/lib/Transforms/Utils/SCCPSolver.cpp
@@ -245,11 +245,46 @@ static Value *simplifyInstruction(SCCPSolver &Solver,
const APInt *RHSC;
// Remove masking operations.
if (match(&Inst, m_And(m_Value(X), m_LowBitMask(RHSC)))) {
- ConstantRange LRange = GetRange(Inst.getOperand(0));
+ ConstantRange LRange = GetRange(X);
if (LRange.getUnsignedMax().ule(*RHSC))
return X;
}
+ if (auto *II = dyn_cast<IntrinsicInst>(&Inst)) {
+ Intrinsic::ID IID = II->getIntrinsicID();
+ // Check if we can simplify [us]cmp(X, Y) to X - Y.
+ if (IID == Intrinsic::scmp || IID == Intrinsic::ucmp) {
+ Value *LHS = II->getOperand(0);
+ Value *RHS = II->getOperand(1);
+ unsigned BitWidth = LHS->getType()->getScalarSizeInBits();
+ ConstantRange LRange = GetRange(LHS);
+ if (LRange.isSizeLargerThan(3))
+ return nullptr;
+ ConstantRange RRange = GetRange(RHS);
+ if (RRange.isSizeLargerThan(3))
+ return nullptr;
+ ConstantRange RHSLower = RRange.sub(APInt(BitWidth, 1));
+ ConstantRange RHSUpper = RRange.add(APInt(BitWidth, 1));
+ ICmpInst::Predicate Pred =
+ IID == Intrinsic::scmp ? CmpInst::ICMP_SLE : CmpInst::ICMP_ULE;
+ if (!RHSLower.icmp(Pred, LRange) || !LRange.icmp(Pred, RHSUpper))
+ return nullptr;
+ Instruction *Sub = BinaryOperator::CreateSub(LHS, RHS, Inst.getName(),
+ Inst.getIterator());
+ if (IID == Intrinsic::scmp)
+ Sub->setHasNoSignedWrap(true);
+ Sub->setDebugLoc(Inst.getDebugLoc());
+ InsertedValues.insert(Sub);
+ if (Sub->getType() != Inst.getType()) {
+ Sub = CastInst::CreateIntegerCast(Sub, Inst.getType(), true, "",
+ Inst.getIterator());
+ Sub->setDebugLoc(Inst.getDebugLoc());
+ InsertedValues.insert(Sub);
+ }
+ return Sub;
+ }
+ }
+
return nullptr;
}
diff --git a/llvm/test/Transforms/SCCP/uscmp.ll b/llvm/test/Transforms/SCCP/uscmp.ll
index 9b9974a93a009..ea5a65556ac55 100644
--- a/llvm/test/Transforms/SCCP/uscmp.ll
+++ b/llvm/test/Transforms/SCCP/uscmp.ll
@@ -4,7 +4,7 @@
define i32 @scmp_to_sub(i32 range(i32 -1, 2) %a) {
; CHECK-LABEL: define i32 @scmp_to_sub(
; CHECK-SAME: i32 range(i32 -1, 2) [[A:%.*]]) {
-; CHECK-NEXT: [[SCMP:%.*]] = call i32 @llvm.scmp.i32.i32(i32 [[A]], i32 0)
+; CHECK-NEXT: [[SCMP:%.*]] = sub nsw i32 [[A]], 0
; CHECK-NEXT: ret i32 [[SCMP]]
;
%scmp = call i32 @llvm.scmp(i32 %a, i32 0)
@@ -16,7 +16,7 @@ define i32 @scmp_zext_to_sub(i1 %a, i1 %b) {
; CHECK-SAME: i1 [[A:%.*]], i1 [[B:%.*]]) {
; CHECK-NEXT: [[ZEXT_A:%.*]] = zext i1 [[A]] to i32
; CHECK-NEXT: [[ZEXT_B:%.*]] = zext i1 [[B]] to i32
-; CHECK-NEXT: [[SCMP:%.*]] = call i32 @llvm.scmp.i32.i32(i32 [[ZEXT_A]], i32 [[ZEXT_B]])
+; CHECK-NEXT: [[SCMP:%.*]] = sub nsw i32 [[ZEXT_A]], [[ZEXT_B]]
; CHECK-NEXT: ret i32 [[SCMP]]
;
%zext_a = zext i1 %a to i32
@@ -28,7 +28,8 @@ define i32 @scmp_zext_to_sub(i1 %a, i1 %b) {
define i8 @scmp_to_sub_trunc(i32 range(i32 -1, 2) %a) {
; CHECK-LABEL: define i8 @scmp_to_sub_trunc(
; CHECK-SAME: i32 range(i32 -1, 2) [[A:%.*]]) {
-; CHECK-NEXT: [[SCMP:%.*]] = call i8 @llvm.scmp.i8.i32(i32 [[A]], i32 0)
+; CHECK-NEXT: [[SCMP1:%.*]] = sub nsw i32 [[A]], 0
+; CHECK-NEXT: [[SCMP:%.*]] = trunc i32 [[SCMP1]] to i8
; CHECK-NEXT: ret i8 [[SCMP]]
;
%scmp = call i8 @llvm.scmp(i32 %a, i32 0)
@@ -38,7 +39,8 @@ define i8 @scmp_to_sub_trunc(i32 range(i32 -1, 2) %a) {
define i64 @scmp_to_sub_sext(i32 range(i32 -1, 2) %a) {
; CHECK-LABEL: define i64 @scmp_to_sub_sext(
; CHECK-SAME: i32 range(i32 -1, 2) [[A:%.*]]) {
-; CHECK-NEXT: [[SCMP:%.*]] = call i64 @llvm.scmp.i64.i32(i32 [[A]], i32 0)
+; CHECK-NEXT: [[SCMP1:%.*]] = sub nsw i32 [[A]], 0
+; CHECK-NEXT: [[SCMP:%.*]] = sext i32 [[SCMP1]] to i64
; CHECK-NEXT: ret i64 [[SCMP]]
;
%scmp = call i64 @llvm.scmp(i32 %a, i32 0)
@@ -48,7 +50,7 @@ define i64 @scmp_to_sub_sext(i32 range(i32 -1, 2) %a) {
define i32 @scmp_to_sub_small_range(i32 range(i32 -1, 1) %a) {
; CHECK-LABEL: define i32 @scmp_to_sub_small_range(
; CHECK-SAME: i32 range(i32 -1, 1) [[A:%.*]]) {
-; CHECK-NEXT: [[SCMP:%.*]] = call i32 @llvm.scmp.i32.i32(i32 [[A]], i32 0)
+; CHECK-NEXT: [[SCMP:%.*]] = sub nsw i32 [[A]], 0
; CHECK-NEXT: ret i32 [[SCMP]]
;
%scmp = call i32 @llvm.scmp(i32 %a, i32 0)
@@ -58,7 +60,7 @@ define i32 @scmp_to_sub_small_range(i32 range(i32 -1, 1) %a) {
define i32 @ucmp_to_sub(i32 range(i32 0, 3) %a) {
; CHECK-LABEL: define i32 @ucmp_to_sub(
; CHECK-SAME: i32 range(i32 0, 3) [[A:%.*]]) {
-; CHECK-NEXT: [[SCMP:%.*]] = call i32 @llvm.scmp.i32.i32(i32 [[A]], i32 1)
+; CHECK-NEXT: [[SCMP:%.*]] = sub nsw i32 [[A]], 1
; CHECK-NEXT: ret i32 [[SCMP]]
;
%scmp = call i32 @llvm.scmp(i32 %a, i32 1)
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