diff --git a/CHANGELOG.md b/CHANGELOG.md
index 6c76a6809d..ef3f326b63 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -52,6 +52,7 @@
 - Improve output of record copying. https://github.com/rescript-lang/rescript-compiler/pull/7043
 - Provide additional context in error message when `unit` is expected. https://github.com/rescript-lang/rescript-compiler/pull/7045
 - Improve error message when passing an object where a record is expected. https://github.com/rescript-lang/rescript-compiler/pull/7101
+- Improve code generation or pattern matching of untagged variants. https://github.com/rescript-lang/rescript-compiler/pull/7128
 
 #### :house: Internal
 
diff --git a/compiler/core/js_exp_make.ml b/compiler/core/js_exp_make.ml
index 5d9c197ddd..5997dafcce 100644
--- a/compiler/core/js_exp_make.ml
+++ b/compiler/core/js_exp_make.ml
@@ -673,6 +673,14 @@ let rec filter_bool (e : t) ~j ~b =
     match (filter_bool e1 ~j ~b, filter_bool e2 ~j ~b) with
     | None, _ | _, None -> None
     | Some e1, Some e2 -> Some {e with expression_desc = Bin (Or, e1, e2)})
+  | Bin (EqEqEq, {expression_desc = Var i}, {expression_desc = Bool b1})
+  | Bin (EqEqEq, {expression_desc = Bool b1}, {expression_desc = Var i})
+    when Js_op_util.same_vident i j ->
+    if b1 = b then None else Some e
+  | Bin (NotEqEq, {expression_desc = Var i}, {expression_desc = Bool b1})
+  | Bin (NotEqEq, {expression_desc = Bool b1}, {expression_desc = Var i})
+    when Js_op_util.same_vident i j ->
+    if b1 <> b then None else Some e
   | Bin
       ( NotEqEq,
         {expression_desc = Typeof {expression_desc = Var i}},
diff --git a/compiler/ml/ast_untagged_variants.ml b/compiler/ml/ast_untagged_variants.ml
index ab53f3961e..5e7df5cd69 100644
--- a/compiler/ml/ast_untagged_variants.ml
+++ b/compiler/ml/ast_untagged_variants.ml
@@ -372,6 +372,14 @@ module DynamicChecks = struct
     | Not of 'a t
     | Expr of 'a
 
+  let rec size = function
+    | BinOp (_, x, y) -> 1 + size x + size y
+    | TagType _ -> 1
+    | TypeOf x -> 1 + size x
+    | IsInstanceOf (_, x) -> 1 + size x
+    | Not x -> 1 + size x
+    | Expr _ -> 1
+
   let bin op x y = BinOp (op, x, y)
   let tag_type t = TagType t
   let typeof x = TypeOf x
@@ -396,7 +404,7 @@ module DynamicChecks = struct
   let ( &&& ) x y = bin And x y
 
   let rec is_a_literal_case ~(literal_cases : tag_type list) ~block_cases
-      (e : _ t) =
+      ~list_literal_cases (e : _ t) =
     let literals_overlaps_with_string () =
       Ext_list.exists literal_cases (function
         | String _ -> true
@@ -458,12 +466,33 @@ module DynamicChecks = struct
           Ext_list.fold_right others is_literal_1 (fun literal_n acc ->
               is_literal_case literal_n ||| acc))
     in
-    match block_cases with
-    | [c] -> is_not_block_case c
-    | c1 :: (_ :: _ as rest) ->
-      is_not_block_case c1
-      &&& is_a_literal_case ~literal_cases ~block_cases:rest e
-    | [] -> assert false
+    if list_literal_cases then
+      let rec mk cases =
+        match List.rev cases with
+        | [case] -> is_literal_case case
+        | case :: rest -> is_literal_case case ||| mk rest
+        | [] -> assert false
+      in
+      mk literal_cases
+    else
+      match block_cases with
+      | [c] -> is_not_block_case c
+      | c1 :: (_ :: _ as rest) ->
+        is_not_block_case c1
+        &&& is_a_literal_case ~literal_cases ~block_cases:rest
+              ~list_literal_cases e
+      | [] -> assert false
+
+  let is_a_literal_case ~literal_cases ~block_cases e =
+    let with_literal_cases =
+      is_a_literal_case ~literal_cases ~block_cases ~list_literal_cases:true e
+    in
+    let without_literal_cases =
+      is_a_literal_case ~literal_cases ~block_cases ~list_literal_cases:false e
+    in
+    if size with_literal_cases <= size without_literal_cases then
+      with_literal_cases
+    else without_literal_cases
 
   let is_int_tag ?(has_null_undefined_other = (false, false, false)) (e : _ t) :
       _ t =
diff --git a/tests/tests/src/UntaggedVariants.mjs b/tests/tests/src/UntaggedVariants.mjs
index 6f59067b7b..6043df57ac 100644
--- a/tests/tests/src/UntaggedVariants.mjs
+++ b/tests/tests/src/UntaggedVariants.mjs
@@ -6,7 +6,7 @@ import * as Primitive_array from "rescript/lib/es6/Primitive_array.js";
 import * as Primitive_option from "rescript/lib/es6/Primitive_option.js";
 
 function classify(x) {
-  if (x === "A" && typeof x !== "number") {
+  if (x === "A") {
     return "A";
   } else if (typeof x === "number") {
     return "An integer";
@@ -40,13 +40,13 @@ let ListWithTuples = {};
 let ListWithObjects = {};
 
 function tuplesToObjects(l) {
-  if (Array.isArray(l)) {
+  if (l === undefined) {
+    return null;
+  } else {
     return {
       hd: l[0],
       tl: tuplesToObjects(l[1])
     };
-  } else {
-    return null;
   }
 }
 
@@ -68,7 +68,7 @@ console.log("l1", l1);
 console.log("l2", l2);
 
 function isTrue(x) {
-  if (typeof x !== "object") {
+  if (x === true) {
     return true;
   } else {
     return x.flag;
@@ -80,7 +80,7 @@ let Truthy = {
 };
 
 function classify$1(x) {
-  if (x === null || typeof x !== "object") {
+  if (x === null || x === undefined) {
     if (x === null) {
       return "null";
     } else {
@@ -112,7 +112,7 @@ let Unknown = {
 };
 
 function classify$3(x) {
-  if (typeof x !== "object" && typeof x !== "number" && (x === "C" || x === "B" || x === "A" || x === "D")) {
+  if (x === "A" || x === "D" || x === "B" || x === "C") {
     switch (x) {
       case "A" :
         return "a";
@@ -173,7 +173,7 @@ let WithArray = {
 };
 
 function classify$6(x) {
-  if (!Array.isArray(x) && (x === null || typeof x !== "object") && typeof x !== "number" && typeof x !== "string") {
+  if (x === false || x === null || x === true) {
     switch (x) {
       case false :
         return "JSONFalse";
@@ -214,18 +214,18 @@ let Json = {
 };
 
 function check(s, y) {
-  if (!Array.isArray(s)) {
+  if (s === "B") {
     return 42;
   }
   let x = s[0];
-  if (!Array.isArray(x)) {
+  if (x === "B") {
     return 42;
   }
   let tmp = s[1];
-  if (Array.isArray(tmp) || x === y) {
-    return 42;
-  } else {
+  if (tmp === "B" && x !== y) {
     return 41;
+  } else {
+    return 42;
   }
 }
 
@@ -234,7 +234,7 @@ let TrickyNested = {
 };
 
 function checkEnum(e) {
-  if (!(e === "Two" || e === "One" || e === "Three")) {
+  if (!(e === "One" || e === "Three" || e === "Two")) {
     return "Something else..." + e;
   }
   switch (e) {
@@ -252,7 +252,7 @@ let OverlapString = {
 };
 
 function checkEnum$1(e) {
-  if (!(e === "Two" || e === 1.0 || e === "Three")) {
+  if (!(e === 1.0 || e === "Three" || e === "Two")) {
     return "Something else...";
   }
   switch (e) {
@@ -376,7 +376,7 @@ let TestFunctionCase = {
 let someJson = '[{"name": "Haan"}, {"name": "Mr"}, false]';
 
 function check$1(s) {
-  if (!Array.isArray(s) && (s === null || typeof s !== "object") && typeof s !== "number" && typeof s !== "string") {
+  if (s === undefined || s === null || s === false || s === true) {
     console.log("Nope...");
     return;
   }
@@ -390,7 +390,7 @@ function check$1(s) {
       let match$1 = s[1];
       if (match$1 === false) {
         let match$2 = s[2];
-        if (!Array.isArray(match$2) && (match$2 === null || typeof match$2 !== "object") && typeof match$2 !== "number" && typeof match$2 !== "string") {
+        if (match$2 === undefined || match$2 === null || match$2 === false || match$2 === true) {
           console.log("Nope...");
           return;
         }
@@ -400,13 +400,13 @@ function check$1(s) {
             return;
           }
           let match$3 = match$2[0];
-          if (!Array.isArray(match$3) && (match$3 === null || typeof match$3 !== "object") && typeof match$3 !== "number" && typeof match$3 !== "string") {
+          if (match$3 === undefined || match$3 === null || match$3 === false || match$3 === true) {
             console.log("Nope...");
             return;
           }
           if (typeof match$3 === "string" && match$3 === "My name is") {
             let match$4 = match$2[1];
-            if (!Array.isArray(match$4) && (match$4 === null || typeof match$4 !== "object") && typeof match$4 !== "number" && typeof match$4 !== "string") {
+            if (match$4 === undefined || match$4 === null || match$4 === false || match$4 === true) {
               console.log("Nope...");
               return;
             }
@@ -476,7 +476,7 @@ let PromiseSync = {
 };
 
 async function classify$10(a) {
-  if (typeof a !== "object" && !(a instanceof Promise) && (a === "test" || a === 12) && !Array.isArray(a)) {
+  if (a === "test" || a === 12) {
     if (a === "test") {
       console.log("testing");
       return;
diff --git a/tests/tests/src/core/Core_JsonTests.mjs b/tests/tests/src/core/Core_JsonTests.mjs
index 8898a2d2b0..0ddd7e6628 100644
--- a/tests/tests/src/core/Core_JsonTests.mjs
+++ b/tests/tests/src/core/Core_JsonTests.mjs
@@ -5,19 +5,19 @@ import * as Test from "./Test.mjs";
 function decodeJsonTest() {
   let json = {"someProp":{"otherProp": null, "thirdProp": [true, false]}};
   let decodedCorrectly;
-  if (!Array.isArray(json) && (json === null || typeof json !== "object") && typeof json !== "number" && typeof json !== "string" && typeof json !== "boolean" || !(typeof json === "object" && !Array.isArray(json))) {
+  if (json === null || !(typeof json === "object" && !Array.isArray(json))) {
     decodedCorrectly = false;
   } else {
     let match = json["someProp"];
-    if (match !== undefined && !(!Array.isArray(match) && (match === null || typeof match !== "object") && typeof match !== "number" && typeof match !== "string" && typeof match !== "boolean" || !(typeof match === "object" && !Array.isArray(match)))) {
+    if (match !== undefined && !(match === null || !(typeof match === "object" && !Array.isArray(match)))) {
       let match$1 = match["thirdProp"];
-      if (match$1 !== undefined && !(!Array.isArray(match$1) && (match$1 === null || typeof match$1 !== "object") && typeof match$1 !== "number" && typeof match$1 !== "string" && typeof match$1 !== "boolean" || !(Array.isArray(match$1) && match$1.length === 2))) {
+      if (match$1 !== undefined && !(match$1 === null || !(Array.isArray(match$1) && match$1.length === 2))) {
         let match$2 = match$1[0];
-        if (!Array.isArray(match$2) && (match$2 === null || typeof match$2 !== "object") && typeof match$2 !== "number" && typeof match$2 !== "string" && typeof match$2 !== "boolean" || !(typeof match$2 === "boolean" && match$2)) {
+        if (match$2 === null || !(typeof match$2 === "boolean" && match$2)) {
           decodedCorrectly = false;
         } else {
           let match$3 = match$1[1];
-          decodedCorrectly = !Array.isArray(match$3) && (match$3 === null || typeof match$3 !== "object") && typeof match$3 !== "number" && typeof match$3 !== "string" && typeof match$3 !== "boolean" || !(typeof match$3 === "boolean" && !match$3) ? false : true;
+          decodedCorrectly = match$3 === null || !(typeof match$3 === "boolean" && !match$3) ? false : true;
         }
       } else {
         decodedCorrectly = false;
diff --git a/tests/tests/src/untagged_variants_heuristic.mjs b/tests/tests/src/untagged_variants_heuristic.mjs
new file mode 100644
index 0000000000..66eb239c11
--- /dev/null
+++ b/tests/tests/src/untagged_variants_heuristic.mjs
@@ -0,0 +1,22 @@
+// Generated by ReScript, PLEASE EDIT WITH CARE
+
+
+function f(x) {
+  if (x !== null) {
+    return;
+  }
+  console.log("abc");
+}
+
+function ff(x) {
+  if (typeof x !== "number") {
+    return;
+  }
+  console.log("abc");
+}
+
+export {
+  f,
+  ff,
+}
+/* No side effect */
diff --git a/tests/tests/src/untagged_variants_heuristic.res b/tests/tests/src/untagged_variants_heuristic.res
new file mode 100644
index 0000000000..2f068b207a
--- /dev/null
+++ b/tests/tests/src/untagged_variants_heuristic.res
@@ -0,0 +1,22 @@
+let f = (x: JSON.t) =>
+  switch x {
+  | Null => Console.log("abc")
+  | _ => ()
+  }
+
+@unboxed
+type t =
+  | A
+  | B
+  | C
+  | D
+  | E
+  | F
+  | G
+  | Int(int)
+
+let ff = (x: t) =>
+  switch x {
+  | Int(_) => Console.log("abc")
+  | _ => ()
+  }
diff --git a/tests/tests/src/variantsMatching.mjs b/tests/tests/src/variantsMatching.mjs
index 0a90661e6a..498102609f 100644
--- a/tests/tests/src/variantsMatching.mjs
+++ b/tests/tests/src/variantsMatching.mjs
@@ -274,7 +274,7 @@ function isWhyNot(x) {
 }
 
 function plus$3(x, y) {
-  if (x === undefined || x === null || x === "WhyNotAnotherOne") {
+  if (x === null || x === "WhyNotAnotherOne" || x === undefined) {
     switch (x) {
       case null :
       case undefined :
@@ -282,13 +282,13 @@ function plus$3(x, y) {
       case "WhyNotAnotherOne" :
         break;
     }
-  } else if (!(y === undefined || y === null || y === "WhyNotAnotherOne")) {
+  } else if (!(y === null || y === "WhyNotAnotherOne" || y === undefined)) {
     return {
       x: x.x + y.x,
       y: x.y + y.y
     };
   }
-  if (!(y === undefined || y === null || y === "WhyNotAnotherOne")) {
+  if (!(y === null || y === "WhyNotAnotherOne" || y === undefined)) {
     return "WhyNotAnotherOne";
   }
   switch (y) {
@@ -301,7 +301,7 @@ function plus$3(x, y) {
 }
 
 function kind$1(x) {
-  if (!(x === undefined || x === null || x === "WhyNotAnotherOne")) {
+  if (!(x === null || x === "WhyNotAnotherOne" || x === undefined)) {
     return "present";
   }
   switch (x) {