[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

Author: AZero13

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);

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)