[InstCombine] smin(smax(X, -1), 1) -> scmp(X, 0) and smax(smin(X, 1), -1) -> scmp(X, 0) #145736

AZero13 · 2025-06-25T16:23:17Z

Motivating case: https://godbolt.org/z/Wxcc51jcj

Alive2: https://alive2.llvm.org/ce/z/-bPPAg

llvmbot · 2025-06-25T16:23:56Z

@llvm/pr-subscribers-llvm-transforms

Author: AZero13 (AZero13)

Changes

Motivating case: https://godbolt.org/z/Wxcc51jcj

Alive2: https://alive2.llvm.org/ce/z/-bPPAg

Full diff: https://github.com/llvm/llvm-project/pull/145736.diff

2 Files Affected:

(modified) llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp (+28)
(modified) llvm/test/Transforms/InstCombine/compare-3way.ll (+80-20)

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
index b6ed1dc4331d2..5f1624abf68e2 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -1920,6 +1920,34 @@ Instruction *InstCombinerImpl::visitCallInst(CallInst &CI) {
   case Intrinsic::smin: {
     Value *I0 = II->getArgOperand(0), *I1 = II->getArgOperand(1);
     Value *X, *Y;
+
+    // smin(smax(X, -1), 1) -> scmp(X, 0)
+    // smax(smin(X, 1), -1) -> scmp(X, 0)
+    // These patterns clamp X to [-1, 1] which is equivalent to a three-way
+    // comparison
+
+    // TODO: Is One use needed? yes it is one intrinisc less, but these do
+    // expand.
+    if (IID == Intrinsic::smin) {
+      if (match(I0, m_OneUse(m_Intrinsic<Intrinsic::smax>(m_Value(X),
+                                                          m_AllOnes()))) &&
+          match(I1, m_One())) {
+        Value *Zero = ConstantInt::get(X->getType(), 0);
+        return replaceInstUsesWith(
+            CI,
+            Builder.CreateIntrinsic(II->getType(), Intrinsic::scmp, {X, Zero}));
+      }
+    }
+
+    if (IID == Intrinsic::smax) {
+      if (match(I0, m_OneUse(m_Intrinsic<Intrinsic::smin>(m_Value(X), m_One()))) &&
+          match(I1, m_AllOnes())) {
+        Value *Zero = ConstantInt::get(X->getType(), 0);
+        return replaceInstUsesWith(CI,
+            Builder.CreateIntrinsic(II->getType(), Intrinsic::scmp, {X, Zero}));
+      }
+    }
+    
     if (match(I0, m_SExt(m_Value(X))) && match(I1, m_SExt(m_Value(Y))) &&
         (I0->hasOneUse() || I1->hasOneUse()) && X->getType() == Y->getType()) {
       Value *NarrowMaxMin = Builder.CreateBinaryIntrinsic(IID, X, Y);
diff --git a/llvm/test/Transforms/InstCombine/compare-3way.ll b/llvm/test/Transforms/InstCombine/compare-3way.ll
index 5d443cd45238c..8f65756775f1b 100644
--- a/llvm/test/Transforms/InstCombine/compare-3way.ll
+++ b/llvm/test/Transforms/InstCombine/compare-3way.ll
@@ -81,8 +81,8 @@ unreached:
 define void @test_low_sle(i64 %a, i64 %b) {
 ; CHECK-LABEL: define void @test_low_sle
 ; CHECK-SAME: (i64 [[A:%.*]], i64 [[B:%.*]]) {
-; CHECK-NEXT:    [[TMP1:%.*]] = icmp slt i64 [[A]], [[B]]
-; CHECK-NEXT:    br i1 [[TMP1]], label [[UNREACHED:%.*]], label [[NORMAL:%.*]]
+; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i64 [[A]], [[B]]
+; CHECK-NEXT:    br i1 [[CMP]], label [[UNREACHED:%.*]], label [[NORMAL:%.*]]
 ; CHECK:       normal:
 ; CHECK-NEXT:    ret void
 ; CHECK:       unreached:
@@ -105,8 +105,8 @@ unreached:
 define void @test_low_ne(i64 %a, i64 %b) {
 ; CHECK-LABEL: define void @test_low_ne
 ; CHECK-SAME: (i64 [[A:%.*]], i64 [[B:%.*]]) {
-; CHECK-NEXT:    [[TMP1:%.*]] = icmp slt i64 [[A]], [[B]]
-; CHECK-NEXT:    br i1 [[TMP1]], label [[NORMAL:%.*]], label [[UNREACHED:%.*]]
+; CHECK-NEXT:    [[CMP_NOT:%.*]] = icmp slt i64 [[A]], [[B]]
+; CHECK-NEXT:    br i1 [[CMP_NOT]], label [[NORMAL:%.*]], label [[UNREACHED:%.*]]
 ; CHECK:       normal:
 ; CHECK-NEXT:    ret void
 ; CHECK:       unreached:
@@ -130,8 +130,8 @@ unreached:
 define void @test_low_eq(i64 %a, i64 %b) {
 ; CHECK-LABEL: define void @test_low_eq
 ; CHECK-SAME: (i64 [[A:%.*]], i64 [[B:%.*]]) {
-; CHECK-NEXT:    [[TMP1:%.*]] = icmp slt i64 [[A]], [[B]]
-; CHECK-NEXT:    br i1 [[TMP1]], label [[UNREACHED:%.*]], label [[NORMAL:%.*]]
+; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i64 [[A]], [[B]]
+; CHECK-NEXT:    br i1 [[CMP]], label [[UNREACHED:%.*]], label [[NORMAL:%.*]]
 ; CHECK:       normal:
 ; CHECK-NEXT:    ret void
 ; CHECK:       unreached:
@@ -154,8 +154,8 @@ unreached:
 define void @test_mid_sgt(i64 %a, i64 %b) {
 ; CHECK-LABEL: define void @test_mid_sgt
 ; CHECK-SAME: (i64 [[A:%.*]], i64 [[B:%.*]]) {
-; CHECK-NEXT:    [[TMP1:%.*]] = icmp sgt i64 [[A]], [[B]]
-; CHECK-NEXT:    br i1 [[TMP1]], label [[UNREACHED:%.*]], label [[NORMAL:%.*]]
+; CHECK-NEXT:    [[CMP:%.*]] = icmp sgt i64 [[A]], [[B]]
+; CHECK-NEXT:    br i1 [[CMP]], label [[UNREACHED:%.*]], label [[NORMAL:%.*]]
 ; CHECK:       normal:
 ; CHECK-NEXT:    ret void
 ; CHECK:       unreached:
@@ -178,8 +178,8 @@ unreached:
 define void @test_mid_slt(i64 %a, i64 %b) {
 ; CHECK-LABEL: define void @test_mid_slt
 ; CHECK-SAME: (i64 [[A:%.*]], i64 [[B:%.*]]) {
-; CHECK-NEXT:    [[TMP1:%.*]] = icmp slt i64 [[A]], [[B]]
-; CHECK-NEXT:    br i1 [[TMP1]], label [[UNREACHED:%.*]], label [[NORMAL:%.*]]
+; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i64 [[A]], [[B]]
+; CHECK-NEXT:    br i1 [[CMP]], label [[UNREACHED:%.*]], label [[NORMAL:%.*]]
 ; CHECK:       normal:
 ; CHECK-NEXT:    ret void
 ; CHECK:       unreached:
@@ -252,8 +252,8 @@ unreached:
 define void @test_mid_ne(i64 %a, i64 %b) {
 ; CHECK-LABEL: define void @test_mid_ne
 ; CHECK-SAME: (i64 [[A:%.*]], i64 [[B:%.*]]) {
-; CHECK-NEXT:    [[EQ:%.*]] = icmp eq i64 [[A]], [[B]]
-; CHECK-NEXT:    br i1 [[EQ]], label [[NORMAL:%.*]], label [[UNREACHED:%.*]]
+; CHECK-NEXT:    [[CMP_NOT:%.*]] = icmp eq i64 [[A]], [[B]]
+; CHECK-NEXT:    br i1 [[CMP_NOT]], label [[NORMAL:%.*]], label [[UNREACHED:%.*]]
 ; CHECK:       normal:
 ; CHECK-NEXT:    ret void
 ; CHECK:       unreached:
@@ -277,8 +277,8 @@ unreached:
 define void @test_mid_eq(i64 %a, i64 %b) {
 ; CHECK-LABEL: define void @test_mid_eq
 ; CHECK-SAME: (i64 [[A:%.*]], i64 [[B:%.*]]) {
-; CHECK-NEXT:    [[EQ:%.*]] = icmp eq i64 [[A]], [[B]]
-; CHECK-NEXT:    br i1 [[EQ]], label [[UNREACHED:%.*]], label [[NORMAL:%.*]]
+; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i64 [[A]], [[B]]
+; CHECK-NEXT:    br i1 [[CMP]], label [[UNREACHED:%.*]], label [[NORMAL:%.*]]
 ; CHECK:       normal:
 ; CHECK-NEXT:    ret void
 ; CHECK:       unreached:
@@ -348,8 +348,8 @@ unreached:
 define void @test_high_sge(i64 %a, i64 %b) {
 ; CHECK-LABEL: define void @test_high_sge
 ; CHECK-SAME: (i64 [[A:%.*]], i64 [[B:%.*]]) {
-; CHECK-NEXT:    [[TMP1:%.*]] = icmp sgt i64 [[A]], [[B]]
-; CHECK-NEXT:    br i1 [[TMP1]], label [[UNREACHED:%.*]], label [[NORMAL:%.*]]
+; CHECK-NEXT:    [[CMP:%.*]] = icmp sgt i64 [[A]], [[B]]
+; CHECK-NEXT:    br i1 [[CMP]], label [[UNREACHED:%.*]], label [[NORMAL:%.*]]
 ; CHECK:       normal:
 ; CHECK-NEXT:    ret void
 ; CHECK:       unreached:
@@ -396,8 +396,8 @@ unreached:
 define void @test_high_ne(i64 %a, i64 %b) {
 ; CHECK-LABEL: define void @test_high_ne
 ; CHECK-SAME: (i64 [[A:%.*]], i64 [[B:%.*]]) {
-; CHECK-NEXT:    [[TMP1:%.*]] = icmp sgt i64 [[A]], [[B]]
-; CHECK-NEXT:    br i1 [[TMP1]], label [[NORMAL:%.*]], label [[UNREACHED:%.*]]
+; CHECK-NEXT:    [[CMP_NOT:%.*]] = icmp sgt i64 [[A]], [[B]]
+; CHECK-NEXT:    br i1 [[CMP_NOT]], label [[NORMAL:%.*]], label [[UNREACHED:%.*]]
 ; CHECK:       normal:
 ; CHECK-NEXT:    ret void
 ; CHECK:       unreached:
@@ -421,8 +421,8 @@ unreached:
 define void @test_high_eq(i64 %a, i64 %b) {
 ; CHECK-LABEL: define void @test_high_eq
 ; CHECK-SAME: (i64 [[A:%.*]], i64 [[B:%.*]]) {
-; CHECK-NEXT:    [[TMP1:%.*]] = icmp sgt i64 [[A]], [[B]]
-; CHECK-NEXT:    br i1 [[TMP1]], label [[UNREACHED:%.*]], label [[NORMAL:%.*]]
+; CHECK-NEXT:    [[CMP:%.*]] = icmp sgt i64 [[A]], [[B]]
+; CHECK-NEXT:    br i1 [[CMP]], label [[UNREACHED:%.*]], label [[NORMAL:%.*]]
 ; CHECK:       normal:
 ; CHECK-NEXT:    ret void
 ; CHECK:       unreached:
@@ -560,3 +560,63 @@ unreached:
   call void @use(i32 %result)
   ret void
 }
+
+define i32 @smax_smin_to_scmp(i32 %x) {
+; CHECK-LABEL: define i32 @smax_smin_to_scmp
+; CHECK-SAME: (i32 [[X:%.*]]) {
+; CHECK-NEXT:    [[COND5:%.*]] = call i32 @llvm.scmp.i32.i32(i32 [[X]], i32 0)
+; CHECK-NEXT:    ret i32 [[COND5]]
+;
+  %cond = call i32 @llvm.smax.i32(i32 %x, i32 -1)
+  %cond5 = call i32 @llvm.smin.i32(i32 %cond, i32 1)
+  ret i32 %cond5
+}
+
+define i16 @smax_smin_to_scmp_i16(i16 %x) {
+; CHECK-LABEL: define i16 @smax_smin_to_scmp_i16
+; CHECK-SAME: (i16 [[X:%.*]]) {
+; CHECK-NEXT:    [[COND5:%.*]] = call i16 @llvm.scmp.i16.i16(i16 [[X]], i16 0)
+; CHECK-NEXT:    ret i16 [[COND5]]
+;
+  %cond = call i16 @llvm.smax.i16(i16 %x, i16 -1)
+  %cond5 = call i16 @llvm.smin.i16(i16 %cond, i16 1)
+  ret i16 %cond5
+}
+
+; Test the reversed pattern: smax(smin(X, 1), -1) -> scmp(X, 0)
+define i32 @smin_smax_to_scmp(i32 %x) {
+; CHECK-LABEL: define i32 @smin_smax_to_scmp
+; CHECK-SAME: (i32 [[X:%.*]]) {
+; CHECK-NEXT:    [[COND5:%.*]] = call i32 @llvm.scmp.i32.i32(i32 [[X]], i32 0)
+; CHECK-NEXT:    ret i32 [[COND5]]
+;
+  %cond = call i32 @llvm.smin.i32(i32 %x, i32 1)
+  %cond5 = call i32 @llvm.smax.i32(i32 %cond, i32 -1)
+  ret i32 %cond5
+}
+
+define i32 @test_max_min_neg(i32 %x) {
+; CHECK-LABEL: define i32 @test_max_min_neg
+; CHECK-SAME: (i32 [[X:%.*]]) {
+; CHECK-NEXT:    [[COND:%.*]] = call i32 @llvm.smax.i32(i32 [[X]], i32 -2)
+; CHECK-NEXT:    [[COND5:%.*]] = call i32 @llvm.smin.i32(i32 [[COND]], i32 1)
+; CHECK-NEXT:    ret i32 [[COND5]]
+;
+  %cond = call i32 @llvm.smax.i32(i32 %x, i32 -2)
+  %cond5 = call i32 @llvm.smin.i32(i32 %cond, i32 1)
+  ret i32 %cond5
+}
+
+define i32 @test_multiple_uses(i32 %x) {
+; CHECK-LABEL: define i32 @test_multiple_uses
+; CHECK-SAME: (i32 [[X:%.*]]) {
+; CHECK-NEXT:    [[COND:%.*]] = call i32 @llvm.smax.i32(i32 [[X]], i32 -1)
+; CHECK-NEXT:    [[COND5:%.*]] = call i32 @llvm.smin.i32(i32 [[COND]], i32 1)
+; CHECK-NEXT:    [[SUM:%.*]] = add i32 [[COND]], [[COND5]]
+; CHECK-NEXT:    ret i32 [[SUM]]
+;
+  %cond = call i32 @llvm.smax.i32(i32 %x, i32 -1)
+  %cond5 = call i32 @llvm.smin.i32(i32 %cond, i32 1)
+  %sum = add i32 %cond, %cond5
+  ret i32 %sum
+}

github-actions · 2025-06-25T16:25:39Z

✅ With the latest revision this PR passed the C/C++ code formatter.

llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp

dtcxzyw · 2025-06-27T13:02:06Z

⚠️ C/C++ code formatter, clang-format found issues in your code. ⚠️

You can test this locally with the following command:

git-clang-format --diff HEAD~1 HEAD --extensions cpp -- llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp

View the diff from clang-format here.

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
index c836ad7ae..1920ee9e4 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -1978,8 +1978,7 @@ Instruction *InstCombinerImpl::visitCallInst(CallInst &CI) {
     // And i1's have been changed to and/ors
     // So we only need to check for smin
     if (IID == Intrinsic::smin) {
-      if (match(I0, m_OneUse(m_SMax(m_Value(X),
-                                                          m_AllOnes()))) &&
+      if (match(I0, m_OneUse(m_SMax(m_Value(X), m_AllOnes()))) &&
           match(I1, m_One())) {
         Value *Zero = ConstantInt::get(X->getType(), 0);
         return replaceInstUsesWith(

Please fix the format.

AZero13 · 2025-06-27T14:10:09Z

⚠️ C/C++ code formatter, clang-format found issues in your code. ⚠️
You can test this locally with the following command:

git-clang-format --diff HEAD~1 HEAD --extensions cpp -- llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp

View the diff from clang-format here.

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
index c836ad7ae..1920ee9e4 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -1978,8 +1978,7 @@ Instruction *InstCombinerImpl::visitCallInst(CallInst &CI) {
     // And i1's have been changed to and/ors
     // So we only need to check for smin
     if (IID == Intrinsic::smin) {
-      if (match(I0, m_OneUse(m_SMax(m_Value(X),
-                                                          m_AllOnes()))) &&
+      if (match(I0, m_OneUse(m_SMax(m_Value(X), m_AllOnes()))) &&
           match(I1, m_One())) {
         Value *Zero = ConstantInt::get(X->getType(), 0);
         return replaceInstUsesWith(

Please fix the format.

Fixed!

nikic

LGTM

llvm/test/Transforms/InstCombine/compare-3way.ll

AZero13 · 2025-06-27T18:07:28Z

@nikic Can you please merge?

llvm/test/Transforms/InstCombine/compare-3way.ll

… -1) -> scmp(X, 0) Motivating case: https://godbolt.org/z/Wxcc51jcj Alive2: https://alive2.llvm.org/ce/z/-bPPAg Co-Authored-By: Nikita Popov <[email protected]> Co-Authored-By: Yingwei Zheng <[email protected]>

AZero13 · 2025-06-28T16:32:17Z

@nikic I do not have merge permissions.

AZero13 requested a review from nikic as a code owner June 25, 2025 16:23

llvmbot added llvm:instcombine Covers the InstCombine, InstSimplify and AggressiveInstCombine passes llvm:transforms labels Jun 25, 2025

AZero13 force-pushed the scmp branch from 78fb682 to 89433db Compare June 25, 2025 16:23

AZero13 force-pushed the scmp branch 4 times, most recently from b53ab34 to db30a00 Compare June 25, 2025 17:10

dtcxzyw reviewed Jun 27, 2025

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This was referenced Jun 27, 2025

Fuzz PR145736 dtcxzyw/llvm-mutation-based-fuzz-service#67

Closed

Task submission dtcxzyw/llvm-opt-benchmark#1312

Open

zyw-bot mentioned this pull request Jun 27, 2025

pre-commit: PR145736 dtcxzyw/llvm-opt-benchmark#2508

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AZero13 force-pushed the scmp branch from b6ebdc1 to 0ed9210 Compare June 27, 2025 13:35

AZero13 requested a review from dtcxzyw June 27, 2025 13:35

nikic approved these changes Jun 27, 2025

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llvm/test/Transforms/InstCombine/compare-3way.ll Show resolved Hide resolved

nikic reviewed Jun 27, 2025

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llvm/test/Transforms/InstCombine/compare-3way.ll Outdated Show resolved Hide resolved

AZero13 and others added 2 commits June 27, 2025 16:19

[InstCombine] Pre-commit tests (NFC)

b16eb26

[InstCombine] smin(smax(X, -1), 1) -> scmp(X, 0) and smax(smin(X, 1),…

a876476

… -1) -> scmp(X, 0) Motivating case: https://godbolt.org/z/Wxcc51jcj Alive2: https://alive2.llvm.org/ce/z/-bPPAg Co-Authored-By: Nikita Popov <[email protected]> Co-Authored-By: Yingwei Zheng <[email protected]>

AZero13 force-pushed the scmp branch from 50cb3b7 to a876476 Compare June 27, 2025 20:19

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[InstCombine] smin(smax(X, -1), 1) -> scmp(X, 0) and smax(smin(X, 1), -1) -> scmp(X, 0) #145736

[InstCombine] smin(smax(X, -1), 1) -> scmp(X, 0) and smax(smin(X, 1), -1) -> scmp(X, 0) #145736

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[InstCombine] smin(smax(X, -1), 1) -> scmp(X, 0) and smax(smin(X, 1), -1) -> scmp(X, 0) #145736

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[InstCombine] smin(smax(X, -1), 1) -> scmp(X, 0) and smax(smin(X, 1), -1) -> scmp(X, 0) #145736

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