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

via llvm-commits llvm-commits at lists.llvm.org
Fri Jun 27 13:07:45 PDT 2025 

https://github.com/AZero13 updated https://github.com/llvm/llvm-project/pull/145736

>From bc144b6213fd6544e4af2b9f16953d2da5e07aaa Mon Sep 17 00:00:00 2001
From: Rose <gfunni234 at gmail.com>
Date: Wed, 25 Jun 2025 11:47:21 -0400
Subject: [PATCH 1/5] [InstCombine] Pre-commit tests (NFC)

---
 .../Transforms/InstCombine/compare-3way.ll    | 105 ++++++++++++++----
 1 file changed, 84 insertions(+), 21 deletions(-)

diff --git a/llvm/test/Transforms/InstCombine/compare-3way.ll b/llvm/test/Transforms/InstCombine/compare-3way.ll
index 5d443cd45238c..b951edac673dc 100644
--- a/llvm/test/Transforms/InstCombine/compare-3way.ll
+++ b/llvm/test/Transforms/InstCombine/compare-3way.ll
@@ -3,7 +3,7 @@
 
 declare void @use(i32)
 
-; These 18 exercise all combinations of signed comparison
+; These exercise all combinations of signed comparison
 ; for each of the three values produced by your typical
 ; 3way compare function (-1, 0, 1)
 
@@ -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 +560,66 @@ 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:    [[COND:%.*]] = call i32 @llvm.smax.i32(i32 [[X]], i32 -1)
+; 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 -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:    [[COND:%.*]] = call i16 @llvm.smax.i16(i16 [[X]], i16 -1)
+; CHECK-NEXT:    [[COND5:%.*]] = call i16 @llvm.smin.i16(i16 [[COND]], i16 1)
+; 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:    [[TMP1:%.*]] = call i32 @llvm.smax.i32(i32 [[X]], i32 -1)
+; CHECK-NEXT:    [[COND5:%.*]] = call i32 @llvm.smin.i32(i32 [[TMP1]], i32 1)
+; 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
+}

>From 0ed9210970f60ae27530581a4fd7250bd8e465eb Mon Sep 17 00:00:00 2001
From: Rose <gfunni234 at gmail.com>
Date: Wed, 25 Jun 2025 12:22:35 -0400
Subject: [PATCH 2/5] [InstCombine] smin(smax(X, -1), 1) -> scmp(X, 0) and
 smax(smin(X, 1), -1) -> scmp(X, 0)

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

Alive2: https://alive2.llvm.org/ce/z/-bPPAg
Co-Authored-By: Yingwei Zheng <dtcxzyw at qq.com>
---
 .../Transforms/InstCombine/InstCombineCalls.cpp   | 15 +++++++++++++++
 llvm/test/Transforms/InstCombine/compare-3way.ll  |  9 +++------
 2 files changed, 18 insertions(+), 6 deletions(-)

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
index b6ed1dc4331d2..1920ee9e4c1aa 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -1972,6 +1972,21 @@ Instruction *InstCombinerImpl::visitCallInst(CallInst &CI) {
       return BinaryOperator::CreateOr(I0, I1);
     }
 
+    // smin(smax(X, -1), 1) -> scmp(X, 0)
+    // smax(smin(X, 1), -1) -> scmp(X, 0)
+    // At this point, smax(smin(X, 1), -1) is changed to smin(smax(X, -1)
+    // 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()))) &&
+          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 || IID == Intrinsic::smin) {
       // smax (neg nsw X), (neg nsw Y) --> neg nsw (smin X, Y)
       // smin (neg nsw X), (neg nsw Y) --> neg nsw (smax X, Y)
diff --git a/llvm/test/Transforms/InstCombine/compare-3way.ll b/llvm/test/Transforms/InstCombine/compare-3way.ll
index b951edac673dc..ea9aa0299c52e 100644
--- a/llvm/test/Transforms/InstCombine/compare-3way.ll
+++ b/llvm/test/Transforms/InstCombine/compare-3way.ll
@@ -564,8 +564,7 @@ unreached:
 define i32 @smax_smin_to_scmp(i32 %x) {
 ; CHECK-LABEL: define i32 @smax_smin_to_scmp
 ; 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:    [[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)
@@ -576,8 +575,7 @@ define i32 @smax_smin_to_scmp(i32 %x) {
 define i16 @smax_smin_to_scmp_i16(i16 %x) {
 ; CHECK-LABEL: define i16 @smax_smin_to_scmp_i16
 ; CHECK-SAME: (i16 [[X:%.*]]) {
-; CHECK-NEXT:    [[COND:%.*]] = call i16 @llvm.smax.i16(i16 [[X]], i16 -1)
-; CHECK-NEXT:    [[COND5:%.*]] = call i16 @llvm.smin.i16(i16 [[COND]], i16 1)
+; 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)
@@ -589,8 +587,7 @@ define i16 @smax_smin_to_scmp_i16(i16 %x) {
 define i32 @smin_smax_to_scmp(i32 %x) {
 ; CHECK-LABEL: define i32 @smin_smax_to_scmp
 ; CHECK-SAME: (i32 [[X:%.*]]) {
-; CHECK-NEXT:    [[TMP1:%.*]] = call i32 @llvm.smax.i32(i32 [[X]], i32 -1)
-; CHECK-NEXT:    [[COND5:%.*]] = call i32 @llvm.smin.i32(i32 [[TMP1]], i32 1)
+; 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)

>From b432c151fd9c1984447313e51e38d20950593de7 Mon Sep 17 00:00:00 2001
From: AZero13 <gfunni234 at gmail.com>
Date: Fri, 27 Jun 2025 13:52:21 -0400
Subject: [PATCH 3/5] More tests

---
 llvm/test/Transforms/InstCombine/compare-3way.ll | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/llvm/test/Transforms/InstCombine/compare-3way.ll b/llvm/test/Transforms/InstCombine/compare-3way.ll
index ea9aa0299c52e..b83b416c18e30 100644
--- a/llvm/test/Transforms/InstCombine/compare-3way.ll
+++ b/llvm/test/Transforms/InstCombine/compare-3way.ll
@@ -607,6 +607,18 @@ define i32 @test_max_min_neg(i32 %x) {
   ret i32 %cond5
 }
 
+define i32 @test_max_min_neg_2(i32 %x) {
+; CHECK-LABEL: define i32 @test_max_min_neg_2
+; 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:%.*]]) {

>From a235880587295b0139174f6a4c4fd1fce3fdfa69 Mon Sep 17 00:00:00 2001
From: AZero13 <gfunni234 at gmail.com>
Date: Fri, 27 Jun 2025 14:45:04 -0400
Subject: [PATCH 4/5] Fix

---
 llvm/test/Transforms/InstCombine/compare-3way.ll | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/llvm/test/Transforms/InstCombine/compare-3way.ll b/llvm/test/Transforms/InstCombine/compare-3way.ll
index b83b416c18e30..7d9bfe43873c9 100644
--- a/llvm/test/Transforms/InstCombine/compare-3way.ll
+++ b/llvm/test/Transforms/InstCombine/compare-3way.ll
@@ -610,9 +610,7 @@ define i32 @test_max_min_neg(i32 %x) {
 define i32 @test_max_min_neg_2(i32 %x) {
 ; CHECK-LABEL: define i32 @test_max_min_neg_2
 ; 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]]
+; CHECK-NEXT:    ret i32 -1
 ;
   %cond = call i32 @llvm.smax.i32(i32 %x, i32 2)
   %cond5 = call i32 @llvm.smin.i32(i32 %cond, i32 -1)

>From 2bded0bf7fdb671ec0f662c106f5ec48e94b7c20 Mon Sep 17 00:00:00 2001
From: AZero13 <gfunni234 at gmail.com>
Date: Fri, 27 Jun 2025 16:07:34 -0400
Subject: [PATCH 5/5] Update compare-3way.ll

Co-authored-by: Nikita Popov <github at npopov.com>
---
 llvm/test/Transforms/InstCombine/compare-3way.ll | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/llvm/test/Transforms/InstCombine/compare-3way.ll b/llvm/test/Transforms/InstCombine/compare-3way.ll
index 7d9bfe43873c9..307c79749b517 100644
--- a/llvm/test/Transforms/InstCombine/compare-3way.ll
+++ b/llvm/test/Transforms/InstCombine/compare-3way.ll
@@ -612,8 +612,8 @@ define i32 @test_max_min_neg_2(i32 %x) {
 ; CHECK-SAME: (i32 [[X:%.*]]) {
 ; CHECK-NEXT:    ret i32 -1
 ;
-  %cond = call i32 @llvm.smax.i32(i32 %x, i32 2)
-  %cond5 = call i32 @llvm.smin.i32(i32 %cond, i32 -1)
+  %cond = call i32 @llvm.smax.i32(i32 %x, i32 -1)
+  %cond5 = call i32 @llvm.smin.i32(i32 %cond, i32 2)
   ret i32 %cond5
 }

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