[LVI][CVP] Treat undef like a full range (#68190)

When converting to ConstantRange, we should treat undef like a full range.
Fixes #68381.

Author: dianqk

llvm/lib/Analysis/LazyValueInfo.cpp

@@ -801,7 +801,7 @@ void LazyValueInfoImpl::intersectAssumeOrGuardBlockValueConstantRange(
 
 static ConstantRange getConstantRangeOrFull(const ValueLatticeElement &Val,
                                             Type *Ty, const DataLayout &DL) {
-  if (Val.isConstantRange())
+  if (Val.isConstantRange(/*UndefAllowed*/ false))
     return Val.getConstantRange();
   return ConstantRange::getFull(DL.getTypeSizeInBits(Ty));
 }

llvm/test/Transforms/CorrelatedValuePropagation/merge-range-and-undef.ll

@@ -382,3 +382,40 @@ exit: ; CVP only simplifies based on ranges for non-local conditions.
   call void @use(i1 %t.1)
   ret i64 %res
 }
+
+; Test case for PR68381.
+; Because of `undef`, we can only delete the second `and` instruction.
+define i32 @constant_range_and_undef_and(i1 %c0, i1 %c1, i8 %v1, i8 %v2) {
+; CHECK-LABEL: @constant_range_and_undef_and(
+; CHECK-NEXT:  start:
+; CHECK-NEXT:    br i1 [[C0:%.*]], label [[BB0:%.*]], label [[BB1:%.*]]
+; CHECK:       bb0:
+; CHECK-NEXT:    [[V1_I32:%.*]] = zext i8 [[V1:%.*]] to i32
+; CHECK-NEXT:    br label [[BB1]]
+; CHECK:       bb1:
+; CHECK-NEXT:    [[X:%.*]] = phi i32 [ [[V1_I32]], [[BB0]] ], [ undef, [[START:%.*]] ]
+; CHECK-NEXT:    br i1 [[C1:%.*]], label [[BB0]], label [[BB2:%.*]]
+; CHECK:       bb2:
+; CHECK-NEXT:    [[V2_I32:%.*]] = zext i8 [[V2:%.*]] to i32
+; CHECK-NEXT:    [[Y:%.*]] = or i32 [[X]], [[V2_I32]]
+; CHECK-NEXT:    [[Z:%.*]] = and i32 [[Y]], 255
+; CHECK-NEXT:    ret i32 [[Z]]
+;
+start:
+  br i1 %c0, label %bb0, label %bb1
+
+bb0:
+  %v1_i32 = zext i8 %v1 to i32
+  br label %bb1
+
+bb1:
+  %x = phi i32 [ %v1_i32, %bb0 ], [ undef, %start ]
+  br i1 %c1, label %bb0, label %bb2
+
+bb2:
+  %v2_i32 = zext i8 %v2 to i32
+  %y = or i32 %x, %v2_i32
+  %z = and i32 %y, 255
+  %z1 = and i32 %z, 255
+  ret i32 %z1
+}