Implement the fold

Author: Poseydon42

llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp

@@ -3551,9 +3551,7 @@ Instruction *InstCombinerImpl::foldSelectToCmp(SelectInst &SI) {
     Pred = ICmpInst::getSwappedPredicate(Pred);
     std::swap(LHS, RHS);
   }
-
-  Intrinsic::ID IID =
-      ICmpInst::isSigned(Pred) ? Intrinsic::scmp : Intrinsic::ucmp;
+  bool IsSigned = ICmpInst::isSigned(Pred);
 
   bool Replace = false;
   ICmpInst::Predicate ExtendedCmpPredicate;
@@ -3575,6 +3573,33 @@ Instruction *InstCombinerImpl::foldSelectToCmp(SelectInst &SI) {
        ICmpInst::getSwappedPredicate(ExtendedCmpPredicate) == Pred))
     Replace = true;
 
+  // (x == y) ? 0 : (x > y ? 1 : -1)
+  ICmpInst::Predicate FalseBranchSelectPredicate;
+  ConstantInt *InnerTV, *InnerFV;
+  if (Pred == ICmpInst::ICMP_EQ && match(TV, m_Zero()) &&
+      match(FV, m_Select(m_c_ICmp(FalseBranchSelectPredicate, m_Specific(LHS),
+                                  m_Specific(RHS)),
+                         m_ConstantInt(InnerTV), m_ConstantInt(InnerFV)))) {
+    if (!ICmpInst::isGT(FalseBranchSelectPredicate)) {
+      FalseBranchSelectPredicate =
+          ICmpInst::getSwappedPredicate(FalseBranchSelectPredicate);
+      std::swap(LHS, RHS);
+    }
+
+    if (!InnerTV->isOne()) {
+      std::swap(InnerTV, InnerFV);
+      std::swap(LHS, RHS);
+    }
+
+    if (ICmpInst::isGT(FalseBranchSelectPredicate) && InnerTV->isOne() &&
+        InnerFV->isAllOnesValue()) {
+      IsSigned = ICmpInst::isSigned(FalseBranchSelectPredicate);
+      Replace = true;
+    }
+  }
+
+  Intrinsic::ID IID =
+      IsSigned ? Intrinsic::scmp : Intrinsic::ucmp;
   if (Replace)
     return replaceInstUsesWith(
         SI, Builder.CreateIntrinsic(SI.getType(), IID, {LHS, RHS}));

llvm/test/Transforms/InstCombine/scmp.ll

@@ -348,10 +348,7 @@ define i8 @scmp_from_select_gt_and_lt(i32 %x, i32 %y) {
 define i8 @scmp_from_select_eq_and_gt(i32 %x, i32 %y) {
 ; CHECK-LABEL: define i8 @scmp_from_select_eq_and_gt(
 ; CHECK-SAME: i32 [[X:%.*]], i32 [[Y:%.*]]) {
-; CHECK-NEXT:    [[EQ:%.*]] = icmp eq i32 [[X]], [[Y]]
-; CHECK-NEXT:    [[GT:%.*]] = icmp sgt i32 [[X]], [[Y]]
-; CHECK-NEXT:    [[SEL1:%.*]] = select i1 [[GT]], i8 1, i8 -1
-; CHECK-NEXT:    [[R:%.*]] = select i1 [[EQ]], i8 0, i8 [[SEL1]]
+; CHECK-NEXT:    [[R:%.*]] = call i8 @llvm.scmp.i8.i32(i32 [[X]], i32 [[Y]])
 ; CHECK-NEXT:    ret i8 [[R]]
 ;
   %eq = icmp eq i32 %x, %y
@@ -364,10 +361,7 @@ define i8 @scmp_from_select_eq_and_gt(i32 %x, i32 %y) {
 define i8 @scmp_from_select_eq_and_gt_commuted1(i32 %x, i32 %y) {
 ; CHECK-LABEL: define i8 @scmp_from_select_eq_and_gt_commuted1(
 ; CHECK-SAME: i32 [[X:%.*]], i32 [[Y:%.*]]) {
-; CHECK-NEXT:    [[EQ:%.*]] = icmp eq i32 [[X]], [[Y]]
-; CHECK-NEXT:    [[GT:%.*]] = icmp slt i32 [[X]], [[Y]]
-; CHECK-NEXT:    [[SEL1:%.*]] = select i1 [[GT]], i8 1, i8 -1
-; CHECK-NEXT:    [[R:%.*]] = select i1 [[EQ]], i8 0, i8 [[SEL1]]
+; CHECK-NEXT:    [[R:%.*]] = call i8 @llvm.scmp.i8.i32(i32 [[Y]], i32 [[X]])
 ; CHECK-NEXT:    ret i8 [[R]]
 ;
   %eq = icmp eq i32 %x, %y
@@ -380,10 +374,7 @@ define i8 @scmp_from_select_eq_and_gt_commuted1(i32 %x, i32 %y) {
 define i8 @scmp_from_select_eq_and_gt_commuted2(i32 %x, i32 %y) {
 ; CHECK-LABEL: define i8 @scmp_from_select_eq_and_gt_commuted2(
 ; CHECK-SAME: i32 [[X:%.*]], i32 [[Y:%.*]]) {
-; CHECK-NEXT:    [[EQ:%.*]] = icmp eq i32 [[X]], [[Y]]
-; CHECK-NEXT:    [[GT:%.*]] = icmp sgt i32 [[X]], [[Y]]
-; CHECK-NEXT:    [[SEL1:%.*]] = select i1 [[GT]], i8 -1, i8 1
-; CHECK-NEXT:    [[R:%.*]] = select i1 [[EQ]], i8 0, i8 [[SEL1]]
+; CHECK-NEXT:    [[R:%.*]] = call i8 @llvm.scmp.i8.i32(i32 [[Y]], i32 [[X]])
 ; CHECK-NEXT:    ret i8 [[R]]
 ;
   %eq = icmp eq i32 %x, %y
@@ -396,10 +387,7 @@ define i8 @scmp_from_select_eq_and_gt_commuted2(i32 %x, i32 %y) {
 define i8 @scmp_from_select_eq_and_gt_commuted3(i32 %x, i32 %y) {
 ; CHECK-LABEL: define i8 @scmp_from_select_eq_and_gt_commuted3(
 ; CHECK-SAME: i32 [[X:%.*]], i32 [[Y:%.*]]) {
-; CHECK-NEXT:    [[EQ:%.*]] = icmp eq i32 [[X]], [[Y]]
-; CHECK-NEXT:    [[GT:%.*]] = icmp slt i32 [[X]], [[Y]]
-; CHECK-NEXT:    [[SEL1:%.*]] = select i1 [[GT]], i8 -1, i8 1
-; CHECK-NEXT:    [[R:%.*]] = select i1 [[EQ]], i8 0, i8 [[SEL1]]
+; CHECK-NEXT:    [[R:%.*]] = call i8 @llvm.scmp.i8.i32(i32 [[X]], i32 [[Y]])
 ; CHECK-NEXT:    ret i8 [[R]]
 ;
   %eq = icmp eq i32 %x, %y

llvm/test/Transforms/InstCombine/ucmp.ll

@@ -546,10 +546,7 @@ define i8 @ucmp_from_select_gt_and_lt(i32 %x, i32 %y) {
 define i8 @scmp_from_select_eq_and_gt(i32 %x, i32 %y) {
 ; CHECK-LABEL: define i8 @scmp_from_select_eq_and_gt(
 ; CHECK-SAME: i32 [[X:%.*]], i32 [[Y:%.*]]) {
-; CHECK-NEXT:    [[EQ:%.*]] = icmp eq i32 [[X]], [[Y]]
-; CHECK-NEXT:    [[GT:%.*]] = icmp ugt i32 [[X]], [[Y]]
-; CHECK-NEXT:    [[SEL1:%.*]] = select i1 [[GT]], i8 1, i8 -1
-; CHECK-NEXT:    [[R:%.*]] = select i1 [[EQ]], i8 0, i8 [[SEL1]]
+; CHECK-NEXT:    [[R:%.*]] = call i8 @llvm.ucmp.i8.i32(i32 [[X]], i32 [[Y]])
 ; CHECK-NEXT:    ret i8 [[R]]
 ;
   %eq = icmp eq i32 %x, %y