[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: Nikita Popov <[email protected]>
Co-Authored-By: Yingwei Zheng <[email protected]>

Author: 3 people

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)

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)
@@ -610,6 +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 -1)
+; CHECK-NEXT:    [[COND5:%.*]] = call i32 @llvm.smin.i32(i32 [[COND]], i32 2)
+; CHECK-NEXT:    ret i32 [[COND5]]
+;
+  %cond = call i32 @llvm.smax.i32(i32 %x, i32 -1)
+  %cond5 = call i32 @llvm.smin.i32(i32 %cond, i32 2)
+  ret i32 %cond5
+}
+
 define i32 @test_multiple_uses(i32 %x) {
 ; CHECK-LABEL: define i32 @test_multiple_uses
 ; CHECK-SAME: (i32 [[X:%.*]]) {