[InstSimplify] Add constant folding support for ucmp/scmp intrinsics (#93730)

This PR adds support for folding calls to `ucmp`/`scmp` intrinsics with
constant arguments.

Author: Poseydon42

llvm/lib/Analysis/ConstantFolding.cpp

@@ -1504,6 +1504,8 @@ bool llvm::canConstantFoldCallTo(const CallBase *Call, const Function *F) {
   case Intrinsic::smin:
   case Intrinsic::umax:
   case Intrinsic::umin:
+  case Intrinsic::scmp:
+  case Intrinsic::ucmp:
   case Intrinsic::sadd_with_overflow:
   case Intrinsic::uadd_with_overflow:
   case Intrinsic::ssub_with_overflow:
@@ -2773,6 +2775,21 @@ static Constant *ConstantFoldIntrinsicCall2(Intrinsic::ID IntrinsicID, Type *Ty,
                   ? *C0
                   : *C1);
 
+    case Intrinsic::scmp:
+    case Intrinsic::ucmp:
+      if (isa<PoisonValue>(Operands[0]) || isa<PoisonValue>(Operands[1]))
+        return PoisonValue::get(Ty);
+
+      if (!C0 || !C1)
+        return ConstantInt::get(Ty, 0);
+
+      int Res;
+      if (IntrinsicID == Intrinsic::scmp)
+        Res = C0->sgt(*C1) ? 1 : C0->slt(*C1) ? -1 : 0;
+      else
+        Res = C0->ugt(*C1) ? 1 : C0->ult(*C1) ? -1 : 0;
+      return ConstantInt::get(Ty, Res, /*IsSigned=*/true);
+
     case Intrinsic::usub_with_overflow:
     case Intrinsic::ssub_with_overflow:
       // X - undef -> { 0, false }

llvm/test/Transforms/InstSimplify/uscmp.ll

@@ -0,0 +1,98 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt < %s -passes=instsimplify -S | FileCheck %s
+
+define i8 @scmp_lt() {
+; CHECK-LABEL: define i8 @scmp_lt() {
+; CHECK-NEXT:    ret i8 -1
+;
+  %1 = call i8 @llvm.scmp(i32 -7, i32 3)
+  ret i8 %1
+}
+
+define i8 @scmp_eq() {
+; CHECK-LABEL: define i8 @scmp_eq() {
+; CHECK-NEXT:    ret i8 0
+;
+  %1 = call i8 @llvm.scmp(i32 2, i32 2)
+  ret i8 %1
+}
+
+define i8 @scmp_gt() {
+; CHECK-LABEL: define i8 @scmp_gt() {
+; CHECK-NEXT:    ret i8 1
+;
+  %1 = call i8 @llvm.scmp(i32 2, i32 -7)
+  ret i8 %1
+}
+
+define i8 @ucmp_lt() {
+; CHECK-LABEL: define i8 @ucmp_lt() {
+; CHECK-NEXT:    ret i8 -1
+;
+  %1 = call i8 @llvm.ucmp(i32 7, i32 12)
+  ret i8 %1
+}
+
+define i2 @ucmp_eq() {
+; CHECK-LABEL: define i2 @ucmp_eq() {
+; CHECK-NEXT:    ret i2 0
+;
+  %1 = call i2 @llvm.ucmp(i32 12, i32 12)
+  ret i2 %1
+}
+
+define i100 @ucmp_gt() {
+; CHECK-LABEL: define i100 @ucmp_gt() {
+; CHECK-NEXT:    ret i100 1
+;
+  %1 = call i100 @llvm.ucmp(i32 7, i32 3)
+  ret i100 %1
+}
+
+define i8 @ucmp_poison() {
+; CHECK-LABEL: define i8 @ucmp_poison() {
+; CHECK-NEXT:    ret i8 poison
+;
+  %1 = call i8 @llvm.ucmp(i32 poison, i32 5)
+  ret i8 %1
+}
+
+define i8 @scmp_poison() {
+; CHECK-LABEL: define i8 @scmp_poison() {
+; CHECK-NEXT:    ret i8 poison
+;
+  %1 = call i8 @llvm.scmp(i32 0, i32 poison)
+  ret i8 %1
+}
+
+define i8 @scmp_undef() {
+; CHECK-LABEL: define i8 @scmp_undef() {
+; CHECK-NEXT:    ret i8 0
+;
+  %1 = call i8 @llvm.scmp(i32 undef, i32 -12)
+  ret i8 %1
+}
+
+define i8 @ucmp_undef() {
+; CHECK-LABEL: define i8 @ucmp_undef() {
+; CHECK-NEXT:    ret i8 0
+;
+  %1 = call i8 @llvm.ucmp(i32 2, i32 undef)
+  ret i8 %1
+}
+
+define <4 x i8> @ucmp_lt_splat() {
+; CHECK-LABEL: define <4 x i8> @ucmp_lt_splat() {
+; CHECK-NEXT:    ret <4 x i8> <i8 -1, i8 -1, i8 -1, i8 -1>
+;
+  %1 = call <4 x i8> @llvm.ucmp(<4 x i32> splat(i32 1), <4 x i32> splat(i32 3))
+  ret <4 x i8> %1
+}
+
+define <4 x i8> @scmp_nonsplat() {
+; CHECK-LABEL: define <4 x i8> @scmp_nonsplat() {
+; CHECK-NEXT:    ret <4 x i8> <i8 1, i8 0, i8 1, i8 -1>
+;
+  %1 = call <4 x i8> @llvm.scmp(<4 x i32> <i32 0, i32 1, i32 2, i32 3>, <4 x i32> <i32 -1, i32 1, i32 -2, i32 4>)
+  ret <4 x i8> %1
+}