[InstCombine] Add a >= b - a<=b to scmp and ucmp folds

https://alive2.llvm.org/ce/z/QiMA_i

Author: AZero13

llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp

@@ -1660,6 +1660,7 @@ Instruction *InstCombinerImpl::visitAdd(BinaryOperator &I) {
     return replaceInstUsesWith(I, Constant::getNullValue(I.getType()));
 
   // sext(A < B) + zext(A > B) => ucmp/scmp(A, B)
+  // sext(A <= B) + zext(A >= B) => ucmp/scmp(A, B)
   CmpPredicate LTPred, GTPred;
   if (match(&I,
             m_c_Add(m_SExt(m_c_ICmp(LTPred, m_Value(A), m_Value(B))),
@@ -1670,13 +1671,50 @@ Instruction *InstCombinerImpl::visitAdd(BinaryOperator &I) {
       std::swap(A, B);
     }
 
-    if (ICmpInst::isLT(LTPred) && ICmpInst::isGT(GTPred) &&
-        ICmpInst::isSigned(LTPred) == ICmpInst::isSigned(GTPred))
-      return replaceInstUsesWith(
-          I, Builder.CreateIntrinsic(
-                 Ty,
-                 ICmpInst::isSigned(LTPred) ? Intrinsic::scmp : Intrinsic::ucmp,
-                 {A, B}));
+    if (ICmpInst::isSigned(LTPred) == ICmpInst::isSigned(GTPred)) {
+      Intrinsic::ID IID =
+          ICmpInst::isSigned(LTPred) ? Intrinsic::scmp : Intrinsic::ucmp;
+
+      // Handle strict inequalities: sext(A < B) + zext(A > B) => scmp/ucmp(A,
+      // B)
+      if (ICmpInst::isLT(LTPred) && ICmpInst::isGT(GTPred)) {
+        return replaceInstUsesWith(I, Builder.CreateIntrinsic(Ty, IID, {A, B}));
+      }
+
+      // Handle non-strict inequalities: sext(A <= B) + zext(A >= B) =>
+      // scmp/ucmp(A, B)
+      if (ICmpInst::isLE(LTPred) && ICmpInst::isGE(GTPred)) {
+        return replaceInstUsesWith(I, Builder.CreateIntrinsic(Ty, IID, {A, B}));
+      }
+    }
+  }
+
+  // Handle constant case: sext(x > C1) + zext(x < C2) where C2 = C1 + 1
+  // This represents (x >= C1+1) - (x <= C1+1) => scmp/ucmp(x, C1+1)
+  Value *X, *Const1, *Const2;
+  CmpPredicate Pred1, Pred2;
+  if (match(&I,
+            m_c_Add(m_SExt(m_c_ICmp(Pred1, m_Value(X), m_Value(Const1))),
+                    m_ZExt(m_c_ICmp(Pred2, m_Deferred(X), m_Value(Const2))))) &&
+      X->getType()->isIntOrIntVectorTy() && isa<ConstantInt>(Const1) &&
+      isa<ConstantInt>(Const2)) {
+
+    // Check if we have x > C1 and x < C2 where C2 = C1 + 2
+    if (ICmpInst::isGT(Pred1) && ICmpInst::isLT(Pred2)) {
+      ConstantInt *ConstC1 = cast<ConstantInt>(Const1);
+      ConstantInt *ConstC2 = cast<ConstantInt>(Const2);
+
+      // Check if C2 = C1 + 2
+      if (ConstC2->getValue() == ConstC1->getValue() + 2) {
+        // This represents (x >= C1+1) - (x <= C1+1) => scmp/ucmp(x, C1+1)
+        Intrinsic::ID IID =
+            ICmpInst::isSigned(Pred1) ? Intrinsic::scmp : Intrinsic::ucmp;
+        Constant *C1Plus1 =
+            ConstantInt::get(Const1->getType(), ConstC1->getValue() + 1);
+        return replaceInstUsesWith(
+            I, Builder.CreateIntrinsic(Ty, IID, {X, C1Plus1}));
+      }
+    }
   }
 
   // A+B --> A|B iff A and B have no bits set in common.

llvm/test/Transforms/InstCombine/sext-a-lt-b-plus-zext-a-gt-b-to-uscmp.ll

@@ -187,11 +187,7 @@ define i8 @signed_add_neg5(i32 %a, i32 %b) {
 define i8 @signed_add_ge_le(i32 %a, i32 %b) {
 ; CHECK-LABEL: define i8 @signed_add_ge_le(
 ; CHECK-SAME: i32 [[A:%.*]], i32 [[B:%.*]]) {
-; CHECK-NEXT:    [[LE:%.*]] = icmp sle i32 [[A]], [[B]]
-; CHECK-NEXT:    [[LE8:%.*]] = sext i1 [[LE]] to i8
-; CHECK-NEXT:    [[GE:%.*]] = icmp sge i32 [[A]], [[B]]
-; CHECK-NEXT:    [[GE8:%.*]] = zext i1 [[GE]] to i8
-; CHECK-NEXT:    [[R:%.*]] = add nsw i8 [[LE8]], [[GE8]]
+; CHECK-NEXT:    [[R:%.*]] = call i8 @llvm.scmp.i8.i32(i32 [[A]], i32 [[B]])
 ; CHECK-NEXT:    ret i8 [[R]]
 ;
   %le = icmp sle i32 %a, %b
@@ -206,11 +202,7 @@ define i8 @signed_add_ge_le(i32 %a, i32 %b) {
 define i8 @unsigned_add_ge_le(i32 %a, i32 %b) {
 ; CHECK-LABEL: define i8 @unsigned_add_ge_le(
 ; CHECK-SAME: i32 [[A:%.*]], i32 [[B:%.*]]) {
-; CHECK-NEXT:    [[LE:%.*]] = icmp ule i32 [[A]], [[B]]
-; CHECK-NEXT:    [[LE8:%.*]] = sext i1 [[LE]] to i8
-; CHECK-NEXT:    [[GE:%.*]] = icmp uge i32 [[A]], [[B]]
-; CHECK-NEXT:    [[GE8:%.*]] = zext i1 [[GE]] to i8
-; CHECK-NEXT:    [[R:%.*]] = add nsw i8 [[LE8]], [[GE8]]
+; CHECK-NEXT:    [[R:%.*]] = call i8 @llvm.ucmp.i8.i32(i32 [[A]], i32 [[B]])
 ; CHECK-NEXT:    ret i8 [[R]]
 ;
   %le = icmp ule i32 %a, %b
@@ -225,11 +217,7 @@ define i8 @unsigned_add_ge_le(i32 %a, i32 %b) {
 define i8 @signed_sub_ge_le(i32 %a, i32 %b) {
 ; CHECK-LABEL: define i8 @signed_sub_ge_le(
 ; CHECK-SAME: i32 [[A:%.*]], i32 [[B:%.*]]) {
-; CHECK-NEXT:    [[LE:%.*]] = icmp sle i32 [[A]], [[B]]
-; CHECK-NEXT:    [[LE8_NEG:%.*]] = sext i1 [[LE]] to i8
-; CHECK-NEXT:    [[GE:%.*]] = icmp sge i32 [[A]], [[B]]
-; CHECK-NEXT:    [[GE8:%.*]] = zext i1 [[GE]] to i8
-; CHECK-NEXT:    [[R:%.*]] = add nsw i8 [[LE8_NEG]], [[GE8]]
+; CHECK-NEXT:    [[R:%.*]] = call i8 @llvm.scmp.i8.i32(i32 [[A]], i32 [[B]])
 ; CHECK-NEXT:    ret i8 [[R]]
 ;
   %le = icmp sle i32 %a, %b
@@ -244,11 +232,7 @@ define i8 @signed_sub_ge_le(i32 %a, i32 %b) {
 define i8 @unsigned_sub_ge_le(i32 %a, i32 %b) {
 ; CHECK-LABEL: define i8 @unsigned_sub_ge_le(
 ; CHECK-SAME: i32 [[A:%.*]], i32 [[B:%.*]]) {
-; CHECK-NEXT:    [[LE:%.*]] = icmp ule i32 [[A]], [[B]]
-; CHECK-NEXT:    [[LE8_NEG:%.*]] = sext i1 [[LE]] to i8
-; CHECK-NEXT:    [[GE:%.*]] = icmp uge i32 [[A]], [[B]]
-; CHECK-NEXT:    [[GE8:%.*]] = zext i1 [[GE]] to i8
-; CHECK-NEXT:    [[R:%.*]] = add nsw i8 [[LE8_NEG]], [[GE8]]
+; CHECK-NEXT:    [[R:%.*]] = call i8 @llvm.ucmp.i8.i32(i32 [[A]], i32 [[B]])
 ; CHECK-NEXT:    ret i8 [[R]]
 ;
   %le = icmp ule i32 %a, %b