[InstSimplify] Provide information about the range of values that UCMP/SCMP can produce to fold some comparisons

Author: Poseydon42

llvm/lib/Analysis/ValueTracking.cpp

@@ -9393,6 +9393,10 @@ static ConstantRange getRangeForIntrinsic(const IntrinsicInst &II) {
     if (!II.getParent() || !II.getFunction())
       break;
     return getVScaleRange(II.getFunction(), Width);
+  case Intrinsic::scmp:
+  case Intrinsic::ucmp:
+    return ConstantRange::getNonEmpty(APInt::getAllOnes(Width),
+                                      APInt::getOneBitSet(Width, 0));
   default:
     break;
   }

llvm/test/Transforms/InstSimplify/uscmp.ll

@@ -232,9 +232,7 @@ define <4 x i8> @ucmp_with_addition_vec(<4 x i32> %x) {
 define i1 @scmp_eq_4(i32 %x, i32 %y) {
 ; CHECK-LABEL: define i1 @scmp_eq_4(
 ; CHECK-SAME: i32 [[X:%.*]], i32 [[Y:%.*]]) {
-; CHECK-NEXT:    [[TMP1:%.*]] = call i8 @llvm.scmp.i8.i32(i32 [[X]], i32 [[Y]])
-; CHECK-NEXT:    [[TMP2:%.*]] = icmp eq i8 [[TMP1]], 4
-; CHECK-NEXT:    ret i1 [[TMP2]]
+; CHECK-NEXT:    ret i1 false
 ;
   %1 = call i8 @llvm.scmp(i32 %x, i32 %y)
   %2 = icmp eq i8 %1, 4
@@ -244,9 +242,7 @@ define i1 @scmp_eq_4(i32 %x, i32 %y) {
 define i1 @ucmp_ne_negative_2(i32 %x, i32 %y) {
 ; CHECK-LABEL: define i1 @ucmp_ne_negative_2(
 ; CHECK-SAME: i32 [[X:%.*]], i32 [[Y:%.*]]) {
-; CHECK-NEXT:    [[TMP1:%.*]] = call i8 @llvm.ucmp.i8.i32(i32 [[X]], i32 [[Y]])
-; CHECK-NEXT:    [[TMP2:%.*]] = icmp ne i8 [[TMP1]], -2
-; CHECK-NEXT:    ret i1 [[TMP2]]
+; CHECK-NEXT:    ret i1 true
 ;
   %1 = call i8 @llvm.ucmp(i32 %x, i32 %y)
   %2 = icmp ne i8 %1, -2