From c9c49f04aebbc9740f77fa6d8cc97ab77980ed41 Mon Sep 17 00:00:00 2001
From: Cristiano Calcagno <cristianoc@users.noreply.github.com>
Date: Fri, 8 Nov 2024 13:34:29 +0100
Subject: [PATCH 01/10] Simplify conditionals.

Fixes https://github.com/rescript-lang/rescript-compiler/issues/7142

- x ? y : false --> x && y
- x ? false : y --> !x && y
- push negation inside when it leads to simplification
---
 compiler/core/js_exp_make.ml                  | 29 ++++++++++++++-----
 lib/es6/Belt_List.js                          |  6 +---
 lib/es6/Belt_Result.js                        | 10 ++-----
 lib/es6/List.js                               |  6 +---
 lib/es6/Primitive_option.js                   |  2 +-
 lib/es6/Result.js                             | 10 ++-----
 lib/js/Belt_List.js                           |  6 +---
 lib/js/Belt_Result.js                         | 10 ++-----
 lib/js/List.js                                |  6 +---
 lib/js/Primitive_option.js                    |  2 +-
 lib/js/Result.js                              | 10 ++-----
 tests/tests/src/UntaggedVariants.mjs          |  6 ++--
 tests/tests/src/bdd.mjs                       |  4 +--
 tests/tests/src/bs_poly_map_test.mjs          |  6 ++--
 tests/tests/src/complex_while_loop.mjs        |  6 ++--
 tests/tests/src/core/Core_NullableTests.mjs   |  4 +--
 tests/tests/src/demo_page.mjs                 |  6 ++--
 .../tests/src/exception_rebound_err_test.mjs  |  2 +-
 tests/tests/src/fib.mjs                       |  6 ++--
 tests/tests/src/gpr_3877_test.mjs             |  6 ++--
 tests/tests/src/gpr_4900_test.mjs             |  4 +--
 tests/tests/src/gpr_4924_test.mjs             |  8 ++---
 tests/tests/src/int_overflow_test.mjs         |  6 ++--
 tests/tests/src/json_decorders.mjs            |  4 +--
 tests/tests/src/test_bool_equal.mjs           |  4 +--
 tests/tests/src/test_demo.mjs                 |  6 ++--
 tests/tests/src/test_fib.mjs                  | 12 ++++----
 tests/tests/src/test_while_side_effect.mjs    |  6 ++--
 tests/tests/src/topsort_test.mjs              |  2 +-
 tests/tests/src/tramp_fib.mjs                 |  6 ++--
 tests/tests/src/variantsMatching.mjs          | 16 ++++++----
 31 files changed, 96 insertions(+), 121 deletions(-)

diff --git a/compiler/core/js_exp_make.ml b/compiler/core/js_exp_make.ml
index cc8d357043..828d3f61dc 100644
--- a/compiler/core/js_exp_make.ml
+++ b/compiler/core/js_exp_make.ml
@@ -997,7 +997,7 @@ let rec simplify_and ~n (e1 : t) (e2 : t) : t option =
              _ ) as is_array) )
       when Js_op_util.same_vident ia ib ->
       Some {expression_desc = is_array; comment = None}
-    | x, y when x = y -> Some e1
+    | _ when Js_analyzer.eq_expression e1 e2 -> Some e1
     | ( Bin
           ( EqEqEq,
             {expression_desc = Var ia},
@@ -1022,7 +1022,9 @@ let rec simplify_and ~n (e1 : t) (e2 : t) : t option =
             ({expression_desc = Bool _ | Null | Undefined _ | Number _ | Str _}
              as v2) ) )
       when Js_op_util.same_vident ia ib && op1 != op2 ->
-      if v1 = v2 then Some false_ else if op1 = EqEqEq then Some e1 else Some e2
+      if Js_analyzer.eq_expression v1 v2 then Some false_
+      else if op1 = EqEqEq then Some e1
+      else Some e2
     | _ -> None
   in
   (if debug then
@@ -1138,7 +1140,10 @@ let not (e : t) : t =
   | Bin (Ge, a, b) -> {e with expression_desc = Bin (Lt, a, b)}
   | Bin (Le, a, b) -> {e with expression_desc = Bin (Gt, a, b)}
   | Bin (Gt, a, b) -> {e with expression_desc = Bin (Le, a, b)}
-  | _ -> {expression_desc = Js_not e; comment = None}
+  | _ -> (
+    match push_negation e with
+    | Some e_ -> e_
+    | None -> {expression_desc = Js_not e; comment = None})
 
 let not_empty_branch (x : t) =
   match x.expression_desc with
@@ -1146,6 +1151,11 @@ let not_empty_branch (x : t) =
   | _ -> true
 
 let rec econd ?comment (pred : t) (ifso : t) (ifnot : t) : t =
+  let default () =
+    if Js_analyzer.eq_expression ifso ifnot then
+      if no_side_effect pred then ifso else seq ?comment pred ifso
+    else {expression_desc = Cond (pred, ifso, ifnot); comment}
+  in
   match (pred.expression_desc, ifso.expression_desc, ifnot.expression_desc) with
   | Bool false, _, _ -> ifnot
   | Number (Int {i = 0l; _}), _, _ -> ifnot
@@ -1179,10 +1189,15 @@ let rec econd ?comment (pred : t) (ifso : t) (ifnot : t) : t =
       Seq (a, {expression_desc = Undefined _}),
       Seq (b, {expression_desc = Undefined _}) ) ->
     seq (econd ?comment pred a b) undefined
-  | _ ->
-    if Js_analyzer.eq_expression ifso ifnot then
-      if no_side_effect pred then ifso else seq ?comment pred ifso
-    else {expression_desc = Cond (pred, ifso, ifnot); comment}
+  | _, _, Bool false -> (
+    match simplify_and ~n:0 pred ifso with
+    | Some e -> e
+    | None -> default ())
+  | _, Bool false, _ -> (
+    match simplify_and ~n:0 (not pred) ifnot with
+    | Some e -> e
+    | None -> default ())
+  | _ -> default ()
 
 let rec float_equal ?comment (e0 : t) (e1 : t) : t =
   match (e0.expression_desc, e1.expression_desc) with
diff --git a/lib/es6/Belt_List.js b/lib/es6/Belt_List.js
index 0991cb4e96..22455cc2e0 100644
--- a/lib/es6/Belt_List.js
+++ b/lib/es6/Belt_List.js
@@ -988,11 +988,7 @@ function eq(_l1, _l2, p) {
     let l2 = _l2;
     let l1 = _l1;
     if (!l1) {
-      if (l2) {
-        return false;
-      } else {
-        return true;
-      }
+      return !l2;
     }
     if (!l2) {
       return false;
diff --git a/lib/es6/Belt_Result.js b/lib/es6/Belt_Result.js
index b83195146a..e534ddd9fe 100644
--- a/lib/es6/Belt_Result.js
+++ b/lib/es6/Belt_Result.js
@@ -57,11 +57,7 @@ function isOk(x) {
 }
 
 function isError(x) {
-  if (x.TAG === "Ok") {
-    return false;
-  } else {
-    return true;
-  }
+  return x.TAG !== "Ok";
 }
 
 function eq(a, b, f) {
@@ -71,10 +67,8 @@ function eq(a, b, f) {
     } else {
       return false;
     }
-  } else if (b.TAG === "Ok") {
-    return false;
   } else {
-    return true;
+    return b.TAG !== "Ok";
   }
 }
 
diff --git a/lib/es6/List.js b/lib/es6/List.js
index 89b2209010..06760467a5 100644
--- a/lib/es6/List.js
+++ b/lib/es6/List.js
@@ -1000,11 +1000,7 @@ function equal(_l1, _l2, p) {
     let l2 = _l2;
     let l1 = _l1;
     if (!l1) {
-      if (l2) {
-        return false;
-      } else {
-        return true;
-      }
+      return !l2;
     }
     if (!l2) {
       return false;
diff --git a/lib/es6/Primitive_option.js b/lib/es6/Primitive_option.js
index 2bdb0ccca9..7d3ab0014e 100644
--- a/lib/es6/Primitive_option.js
+++ b/lib/es6/Primitive_option.js
@@ -44,7 +44,7 @@ function fromNull(x) {
 }
 
 function valFromOption(x) {
-  if (!(x !== null && x.BS_PRIVATE_NESTED_SOME_NONE !== undefined)) {
+  if (x === null || x.BS_PRIVATE_NESTED_SOME_NONE === undefined) {
     return x;
   }
   let depth = x.BS_PRIVATE_NESTED_SOME_NONE;
diff --git a/lib/es6/Result.js b/lib/es6/Result.js
index 5b5023054f..9fc4536c9e 100644
--- a/lib/es6/Result.js
+++ b/lib/es6/Result.js
@@ -51,11 +51,7 @@ function isOk(x) {
 }
 
 function isError(x) {
-  if (x.TAG === "Ok") {
-    return false;
-  } else {
-    return true;
-  }
+  return x.TAG !== "Ok";
 }
 
 function equal(a, b, f) {
@@ -65,10 +61,8 @@ function equal(a, b, f) {
     } else {
       return false;
     }
-  } else if (b.TAG === "Ok") {
-    return false;
   } else {
-    return true;
+    return b.TAG !== "Ok";
   }
 }
 
diff --git a/lib/js/Belt_List.js b/lib/js/Belt_List.js
index f5bf603c2b..2d9f0e17ec 100644
--- a/lib/js/Belt_List.js
+++ b/lib/js/Belt_List.js
@@ -988,11 +988,7 @@ function eq(_l1, _l2, p) {
     let l2 = _l2;
     let l1 = _l1;
     if (!l1) {
-      if (l2) {
-        return false;
-      } else {
-        return true;
-      }
+      return !l2;
     }
     if (!l2) {
       return false;
diff --git a/lib/js/Belt_Result.js b/lib/js/Belt_Result.js
index 0aba2f6f5c..fb2585738a 100644
--- a/lib/js/Belt_Result.js
+++ b/lib/js/Belt_Result.js
@@ -57,11 +57,7 @@ function isOk(x) {
 }
 
 function isError(x) {
-  if (x.TAG === "Ok") {
-    return false;
-  } else {
-    return true;
-  }
+  return x.TAG !== "Ok";
 }
 
 function eq(a, b, f) {
@@ -71,10 +67,8 @@ function eq(a, b, f) {
     } else {
       return false;
     }
-  } else if (b.TAG === "Ok") {
-    return false;
   } else {
-    return true;
+    return b.TAG !== "Ok";
   }
 }
 
diff --git a/lib/js/List.js b/lib/js/List.js
index 129fb6f5cf..8e8cd35fbc 100644
--- a/lib/js/List.js
+++ b/lib/js/List.js
@@ -1000,11 +1000,7 @@ function equal(_l1, _l2, p) {
     let l2 = _l2;
     let l1 = _l1;
     if (!l1) {
-      if (l2) {
-        return false;
-      } else {
-        return true;
-      }
+      return !l2;
     }
     if (!l2) {
       return false;
diff --git a/lib/js/Primitive_option.js b/lib/js/Primitive_option.js
index 53c29aae13..d6d8a9f45b 100644
--- a/lib/js/Primitive_option.js
+++ b/lib/js/Primitive_option.js
@@ -44,7 +44,7 @@ function fromNull(x) {
 }
 
 function valFromOption(x) {
-  if (!(x !== null && x.BS_PRIVATE_NESTED_SOME_NONE !== undefined)) {
+  if (x === null || x.BS_PRIVATE_NESTED_SOME_NONE === undefined) {
     return x;
   }
   let depth = x.BS_PRIVATE_NESTED_SOME_NONE;
diff --git a/lib/js/Result.js b/lib/js/Result.js
index b0c9638920..bee54d5b2f 100644
--- a/lib/js/Result.js
+++ b/lib/js/Result.js
@@ -51,11 +51,7 @@ function isOk(x) {
 }
 
 function isError(x) {
-  if (x.TAG === "Ok") {
-    return false;
-  } else {
-    return true;
-  }
+  return x.TAG !== "Ok";
 }
 
 function equal(a, b, f) {
@@ -65,10 +61,8 @@ function equal(a, b, f) {
     } else {
       return false;
     }
-  } else if (b.TAG === "Ok") {
-    return false;
   } else {
-    return true;
+    return b.TAG !== "Ok";
   }
 }
 
diff --git a/tests/tests/src/UntaggedVariants.mjs b/tests/tests/src/UntaggedVariants.mjs
index 95d20f5767..4a2a4c5fc8 100644
--- a/tests/tests/src/UntaggedVariants.mjs
+++ b/tests/tests/src/UntaggedVariants.mjs
@@ -234,7 +234,7 @@ let TrickyNested = {
 };
 
 function checkEnum(e) {
-  if (!(e === "One" || e === "Three" || e === "Two")) {
+  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 === 1.0 || e === "Three" || e === "Two")) {
+  if (e !== 1.0 && e !== "Three" && e !== "Two") {
     return "Something else...";
   }
   switch (e) {
@@ -270,7 +270,7 @@ let OverlapNumber = {
 };
 
 function checkEnum$2(e) {
-  if (!(e === null || typeof e !== "object")) {
+  if (e !== null && typeof e === "object") {
     return "Object...";
   }
   switch (e) {
diff --git a/tests/tests/src/bdd.mjs b/tests/tests/src/bdd.mjs
index dd2b767d28..ea08036d64 100644
--- a/tests/tests/src/bdd.mjs
+++ b/tests/tests/src/bdd.mjs
@@ -363,10 +363,8 @@ function random_vars(n) {
 function bool_equal(a, b) {
   if (a) {
     return b;
-  } else if (b) {
-    return false;
   } else {
-    return true;
+    return !b;
   }
 }
 
diff --git a/tests/tests/src/bs_poly_map_test.mjs b/tests/tests/src/bs_poly_map_test.mjs
index 5015db4a04..548269bfd8 100644
--- a/tests/tests/src/bs_poly_map_test.mjs
+++ b/tests/tests/src/bs_poly_map_test.mjs
@@ -210,7 +210,7 @@ let match$1 = match[0];
 
 let match$2 = Belt_Map.get(v3, 10);
 
-b("File \"bs_poly_map_test.res\", line 155, characters 4-11", match$2 !== undefined ? match$2 === 11 : false);
+b("File \"bs_poly_map_test.res\", line 155, characters 4-11", match$2 === 11);
 
 let match$3 = Belt_Map.get(v3, -10);
 
@@ -218,13 +218,13 @@ b("File \"bs_poly_map_test.res\", line 162, characters 4-11", match$3 === undefi
 
 let match$4 = Belt_Map.get(v4, -10);
 
-b("File \"bs_poly_map_test.res\", line 169, characters 4-11", match$4 !== undefined ? match$4 === 0 : false);
+b("File \"bs_poly_map_test.res\", line 169, characters 4-11", match$4 === 0);
 
 b("File \"bs_poly_map_test.res\", line 175, characters 4-11", Belt_Map.isEmpty(Belt_Map.remove(Belt_Map.make(Icmp), 0)));
 
 b("File \"bs_poly_map_test.res\", line 176, characters 4-11", Belt_Map.isEmpty(Belt_Map.removeMany(Belt_Map.make(Icmp), [0])));
 
-b("File \"bs_poly_map_test.res\", line 178, characters 4-11", pres !== undefined ? pres === 5000 : false);
+b("File \"bs_poly_map_test.res\", line 178, characters 4-11", pres === 5000);
 
 b("File \"bs_poly_map_test.res\", line 184, characters 4-11", Belt_Array.eq(Belt_Map.keysToArray(match$1[0]), Belt_Array.makeBy(5000, i => i), (prim0, prim1) => prim0 === prim1));
 
diff --git a/tests/tests/src/complex_while_loop.mjs b/tests/tests/src/complex_while_loop.mjs
index 5fd9b2aa27..ad885374a3 100644
--- a/tests/tests/src/complex_while_loop.mjs
+++ b/tests/tests/src/complex_while_loop.mjs
@@ -5,10 +5,10 @@ function f() {
   let n = 0;
   while ((() => {
       let fib = x => {
-        if (x === 0 || x === 1) {
-          return 1;
-        } else {
+        if (x !== 0 && x !== 1) {
           return fib(x - 1 | 0) + fib(x - 2 | 0) | 0;
+        } else {
+          return 1;
         }
       };
       return fib(n) > 10;
diff --git a/tests/tests/src/core/Core_NullableTests.mjs b/tests/tests/src/core/Core_NullableTests.mjs
index 7228bd972c..f781a4e6cc 100644
--- a/tests/tests/src/core/Core_NullableTests.mjs
+++ b/tests/tests/src/core/Core_NullableTests.mjs
@@ -7,7 +7,7 @@ function shouldHandleNullableValues() {
   let tUndefined = undefined;
   let tValue = "hello";
   let tmp;
-  tmp = (tNull == null) ? tNull === null : false;
+  tmp = tNull === null;
   Test.run([
     [
       "Core_NullableTests.res",
@@ -29,7 +29,7 @@ function shouldHandleNullableValues() {
     "Should handle undefined"
   ], tmp$1, (prim0, prim1) => prim0 === prim1, true);
   let tmp$2;
-  tmp$2 = (tValue == null) ? false : tValue === "hello";
+  tmp$2 = tValue === "hello";
   Test.run([
     [
       "Core_NullableTests.res",
diff --git a/tests/tests/src/demo_page.mjs b/tests/tests/src/demo_page.mjs
index ee3b1665a5..cacf467d0b 100644
--- a/tests/tests/src/demo_page.mjs
+++ b/tests/tests/src/demo_page.mjs
@@ -4,10 +4,10 @@ import * as React from "react";
 import * as ReactDom from "react-dom";
 
 function fib(x) {
-  if (x === 2 || x === 1) {
-    return 1;
-  } else {
+  if (x !== 2 && x !== 1) {
     return fib(x - 1 | 0) + fib(x - 2 | 0) | 0;
+  } else {
+    return 1;
   }
 }
 
diff --git a/tests/tests/src/exception_rebound_err_test.mjs b/tests/tests/src/exception_rebound_err_test.mjs
index a43cea2ec0..fcb0d2812e 100644
--- a/tests/tests/src/exception_rebound_err_test.mjs
+++ b/tests/tests/src/exception_rebound_err_test.mjs
@@ -52,7 +52,7 @@ function test_js_error4() {
       }
     } else if (e.RE_EXN_ID === B) {
       return 5;
-    } else if (e.RE_EXN_ID === C && !(e._1 !== 1 || e._2 !== 2)) {
+    } else if (e.RE_EXN_ID === C && e._1 === 1 && e._2 === 2) {
       return 6;
     } else {
       return 7;
diff --git a/tests/tests/src/fib.mjs b/tests/tests/src/fib.mjs
index 40a3b661f3..9c974944f1 100644
--- a/tests/tests/src/fib.mjs
+++ b/tests/tests/src/fib.mjs
@@ -2,10 +2,10 @@
 
 
 function fib(x) {
-  if (x === 0 || x === 1) {
-    return 1;
-  } else {
+  if (x !== 0 && x !== 1) {
     return fib(x - 1 | 0) + fib(x - 2 | 0) | 0;
+  } else {
+    return 1;
   }
 }
 
diff --git a/tests/tests/src/gpr_3877_test.mjs b/tests/tests/src/gpr_3877_test.mjs
index 66f0c8d4ff..2c16b2d958 100644
--- a/tests/tests/src/gpr_3877_test.mjs
+++ b/tests/tests/src/gpr_3877_test.mjs
@@ -3,10 +3,10 @@
 
 function test(code) {
   if (code > 599 || code < 500) {
-    if (code === 201 || code === 200) {
-      return "good response";
-    } else {
+    if (code !== 201 && code !== 200) {
       return "the catch all";
+    } else {
+      return "good response";
     }
   } else if (code > 597 || code < 512) {
     return "bad response";
diff --git a/tests/tests/src/gpr_4900_test.mjs b/tests/tests/src/gpr_4900_test.mjs
index 5d3ef07f54..1113493aeb 100644
--- a/tests/tests/src/gpr_4900_test.mjs
+++ b/tests/tests/src/gpr_4900_test.mjs
@@ -11,8 +11,8 @@ let test_id = {
 };
 
 function showToJs(x) {
-  if (typeof x !== "object" && x === "No") {
-    return false;
+  if (typeof x !== "object") {
+    return x !== "No";
   } else {
     return true;
   }
diff --git a/tests/tests/src/gpr_4924_test.mjs b/tests/tests/src/gpr_4924_test.mjs
index fc3b42303d..03278edbad 100644
--- a/tests/tests/src/gpr_4924_test.mjs
+++ b/tests/tests/src/gpr_4924_test.mjs
@@ -27,8 +27,8 @@ function u1(b) {
 }
 
 function u2(b) {
-  if (typeof b !== "object" && b === "A") {
-    return false;
+  if (typeof b !== "object") {
+    return b !== "A";
   } else {
     return true;
   }
@@ -57,8 +57,8 @@ function u4(b) {
 }
 
 function u5(b) {
-  if (typeof b !== "object" && b === "A") {
-    return false;
+  if (typeof b !== "object") {
+    return b !== "A";
   } else {
     return true;
   }
diff --git a/tests/tests/src/int_overflow_test.mjs b/tests/tests/src/int_overflow_test.mjs
index 8f44d3aae1..192ca3ca25 100644
--- a/tests/tests/src/int_overflow_test.mjs
+++ b/tests/tests/src/int_overflow_test.mjs
@@ -28,10 +28,10 @@ function hash_variant2(s) {
 }
 
 function fib(x) {
-  if (x === 0 || x === 1) {
-    return 1;
-  } else {
+  if (x !== 0 && x !== 1) {
     return fib(x - 1 | 0) + fib(x - 2 | 0) | 0;
+  } else {
+    return 1;
   }
 }
 
diff --git a/tests/tests/src/json_decorders.mjs b/tests/tests/src/json_decorders.mjs
index cac0277cc7..781dfca57d 100644
--- a/tests/tests/src/json_decorders.mjs
+++ b/tests/tests/src/json_decorders.mjs
@@ -3,7 +3,7 @@
 import * as $$Array from "rescript/lib/es6/Array.js";
 
 function decodeUser(json) {
-  if (!(typeof json === "object" && !Array.isArray(json))) {
+  if (typeof json !== "object" || Array.isArray(json)) {
     return;
   }
   let id = json.id;
@@ -30,7 +30,7 @@ function decodeUser(json) {
 }
 
 function decodeGroup(json) {
-  if (!(typeof json === "object" && !Array.isArray(json))) {
+  if (typeof json !== "object" || Array.isArray(json)) {
     return;
   }
   let id = json.id;
diff --git a/tests/tests/src/test_bool_equal.mjs b/tests/tests/src/test_bool_equal.mjs
index 6d0bc4e9d6..d7e5c90a32 100644
--- a/tests/tests/src/test_bool_equal.mjs
+++ b/tests/tests/src/test_bool_equal.mjs
@@ -4,10 +4,8 @@
 function bool_equal(x, y) {
   if (x) {
     return y;
-  } else if (y) {
-    return false;
   } else {
-    return true;
+    return !y;
   }
 }
 
diff --git a/tests/tests/src/test_demo.mjs b/tests/tests/src/test_demo.mjs
index 048494ef32..44e19f2540 100644
--- a/tests/tests/src/test_demo.mjs
+++ b/tests/tests/src/test_demo.mjs
@@ -3,10 +3,10 @@
 import * as Belt_List from "rescript/lib/es6/Belt_List.js";
 
 function fib(x) {
-  if (x === 2 || x === 1) {
-    return 1;
-  } else {
+  if (x !== 2 && x !== 1) {
     return fib(x - 1 | 0) + fib(x - 2 | 0) | 0;
+  } else {
+    return 1;
   }
 }
 
diff --git a/tests/tests/src/test_fib.mjs b/tests/tests/src/test_fib.mjs
index 982775b5a6..4e488a8269 100644
--- a/tests/tests/src/test_fib.mjs
+++ b/tests/tests/src/test_fib.mjs
@@ -2,18 +2,18 @@
 
 
 function fib(x) {
-  if (x === 0 || x === 1) {
-    return 1;
-  } else {
+  if (x !== 0 && x !== 1) {
     return fib(x - 1 | 0) + fib(x - 2 | 0) | 0;
+  } else {
+    return 1;
   }
 }
 
 function fib2(x) {
-  if (x === 2 || x === 1) {
-    return 1;
-  } else {
+  if (x !== 2 && x !== 1) {
     return fib2(x - 1 | 0) + fib2(x - 2 | 0) | 0;
+  } else {
+    return 1;
   }
 }
 
diff --git a/tests/tests/src/test_while_side_effect.mjs b/tests/tests/src/test_while_side_effect.mjs
index 2cbc733d44..315cd3bc1f 100644
--- a/tests/tests/src/test_while_side_effect.mjs
+++ b/tests/tests/src/test_while_side_effect.mjs
@@ -10,10 +10,10 @@ while (console.log(v.contents.toString()), v.contents = v.contents + 1 | 0, v.co
 };
 
 function fib(x) {
-  if (x === 0 || x === 1) {
-    return 1;
-  } else {
+  if (x !== 0 && x !== 1) {
     return fib(x - 1 | 0) + fib(x - 2 | 0) | 0;
+  } else {
+    return 1;
   }
 }
 
diff --git a/tests/tests/src/topsort_test.mjs b/tests/tests/src/topsort_test.mjs
index 90fdebb6c5..2dc512b66a 100644
--- a/tests/tests/src/topsort_test.mjs
+++ b/tests/tests/src/topsort_test.mjs
@@ -545,7 +545,7 @@ try {
         let match$2 = match$1.tl;
         if (match$2 && match$2.hd === "eat") {
           let match$3 = match$2.tl;
-          if (!(match$3 && match$3.hd === "go" && !match$3.tl)) {
+          if (!(match$3 && !(match$3.hd !== "go" || match$3.tl))) {
             exit = 1;
           }
           
diff --git a/tests/tests/src/tramp_fib.mjs b/tests/tests/src/tramp_fib.mjs
index 69ceed051f..2d440bb5a3 100644
--- a/tests/tests/src/tramp_fib.mjs
+++ b/tests/tests/src/tramp_fib.mjs
@@ -15,13 +15,13 @@ function eq(loc, x, y) {
 }
 
 function fib(n, k) {
-  if (n === 0 || n === 1) {
-    return k(1);
-  } else {
+  if (n !== 0 && n !== 1) {
     return {
       TAG: "Suspend",
       _0: () => fib(n - 1 | 0, v0 => fib(n - 2 | 0, v1 => k(v0 + v1 | 0)))
     };
+  } else {
+    return k(1);
   }
 }
 
diff --git a/tests/tests/src/variantsMatching.mjs b/tests/tests/src/variantsMatching.mjs
index e4b281726f..4e367a3740 100644
--- a/tests/tests/src/variantsMatching.mjs
+++ b/tests/tests/src/variantsMatching.mjs
@@ -74,8 +74,8 @@ function st(state) {
 }
 
 function showToJs(x) {
-  if (typeof x !== "object" && x === "No") {
-    return false;
+  if (typeof x !== "object") {
+    return x !== "No";
   } else {
     return true;
   }
@@ -96,7 +96,11 @@ function third(l) {
     return false;
   }
   let match$1 = match.tl;
-  return match$1 && !(match$1.hd !== 3 || match$1.tl);
+  if (match$1 && match$1.hd === 3) {
+    return !match$1.tl;
+  } else {
+    return false;
+  }
 }
 
 function third2(l) {
@@ -274,13 +278,13 @@ function plus$3(x, y) {
       case "WhyNotAnotherOne" :
         break;
     }
-  } else if (!(y === null || y === "WhyNotAnotherOne" || y === undefined)) {
+  } else if (y !== null && y !== "WhyNotAnotherOne" && y !== undefined) {
     return {
       x: x.x + y.x,
       y: x.y + y.y
     };
   }
-  if (!(y === null || y === "WhyNotAnotherOne" || y === undefined)) {
+  if (y !== null && y !== "WhyNotAnotherOne" && y !== undefined) {
     return "WhyNotAnotherOne";
   }
   switch (y) {
@@ -293,7 +297,7 @@ function plus$3(x, y) {
 }
 
 function kind$1(x) {
-  if (!(x === null || x === "WhyNotAnotherOne" || x === undefined)) {
+  if (x !== null && x !== "WhyNotAnotherOne" && x !== undefined) {
     return "present";
   }
   switch (x) {

From 2dad0322838230710998514e59773f240eb22164 Mon Sep 17 00:00:00 2001
From: Cristiano Calcagno <cristianoc@users.noreply.github.com>
Date: Fri, 8 Nov 2024 13:35:35 +0100
Subject: [PATCH 02/10] Update CHANGELOG.md

---
 CHANGELOG.md | 1 +
 1 file changed, 1 insertion(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index ba3fd69f59..6c5ad614c5 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -63,6 +63,7 @@
 - Improve pattern matching on optional fields. https://github.com/rescript-lang/rescript-compiler/pull/7143 https://github.com/rescript-lang/rescript-compiler/pull/7144
 - Optimize compilation of switch statements for untagged variants when there are no literal cases. https://github.com/rescript-lang/rescript-compiler/pull/7135
 - Further improve boolean optimizations. https://github.com/rescript-lang/rescript-compiler/pull/7149
+- Simplify code generated forconditionals. https://github.com/rescript-lang/rescript-compiler/pull/7151
 
 
 #### :house: Internal

From 0d49895dc9f272fdb16ebb704b7a75deec4772d6 Mon Sep 17 00:00:00 2001
From: Cristiano Calcagno <cristianoc@users.noreply.github.com>
Date: Fri, 8 Nov 2024 13:42:08 +0100
Subject: [PATCH 03/10] Squeeze in side effects check

From https://github.com/rescript-lang/rescript-compiler/pull/7149/files#r1834278587
---
 compiler/core/js_exp_make.ml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/compiler/core/js_exp_make.ml b/compiler/core/js_exp_make.ml
index 828d3f61dc..65bea5242b 100644
--- a/compiler/core/js_exp_make.ml
+++ b/compiler/core/js_exp_make.ml
@@ -743,7 +743,7 @@ let rec simplify_and ~n (e1 : t) (e2 : t) : t option =
   let res =
     match (e1.expression_desc, e2.expression_desc) with
     | Bool false, _ -> Some false_
-    | _, Bool false -> Some false_
+    | _, Bool false when no_side_effect e1 -> Some false_
     | Bool true, _ -> Some e2
     | _, Bool true -> Some e1
     | Bin (And, a, b), _ -> (

From 8bb34736e19171caf3ea13c0e911b6bcf39a5d44 Mon Sep 17 00:00:00 2001
From: Cristiano Calcagno <cristianoc@users.noreply.github.com>
Date: Fri, 8 Nov 2024 13:58:25 +0100
Subject: [PATCH 04/10] comment

---
 compiler/core/js_exp_make.ml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/compiler/core/js_exp_make.ml b/compiler/core/js_exp_make.ml
index 65bea5242b..0dfc0166d9 100644
--- a/compiler/core/js_exp_make.ml
+++ b/compiler/core/js_exp_make.ml
@@ -702,7 +702,7 @@ let rec push_negation (e : t) : t option =
   Basic simplification rules:
   - [false && e] -> [false]
   - [true && e] -> [e] 
-  - [e && false] -> [false]
+  - [e && false] -> [false] If [e] has no side effects
   - [e && true] -> [e]
   - [(a && b) && e] -> If either [a && e] or [b && e] can be simplified, 
                        creates new AND expression with simplified parts: [(a' && b')]

From 30a6b2d0b77ae1c376177a897cd54f8eb356b0c7 Mon Sep 17 00:00:00 2001
From: Cristiano Calcagno <cristianoc@users.noreply.github.com>
Date: Sat, 9 Nov 2024 08:37:25 +0100
Subject: [PATCH 05/10] Only apply optimisations when there are no side
 effects.

---
 compiler/core/js_analyzer.ml         |  8 +++--
 compiler/core/js_exp_make.ml         | 48 ++++++++++++++++------------
 tests/tests/src/option_repr_test.mjs |  4 +--
 3 files changed, 35 insertions(+), 25 deletions(-)

diff --git a/compiler/core/js_analyzer.ml b/compiler/core/js_analyzer.ml
index 2b660a025a..7411de8bcf 100644
--- a/compiler/core/js_analyzer.ml
+++ b/compiler/core/js_analyzer.ml
@@ -109,9 +109,11 @@ let rec no_side_effect_expression_desc (x : J.expression_desc) =
     no_side_effect call_expr
     && Ext_list.for_all strings no_side_effect
     && Ext_list.for_all values no_side_effect
-  | Js_not _ | Cond _ | FlatCall _ | Call _ | New _ | Raw_js_code _
-  (* actually true? *) ->
-    false
+  | Js_not e -> no_side_effect e
+  | Cond (a, b, c) -> no_side_effect a && no_side_effect b && no_side_effect c
+  | Call ({expression_desc = Str {txt = "Array.isArray"}}, [e], _) ->
+    no_side_effect e
+  | FlatCall _ | Call _ | New _ | Raw_js_code _ (* actually true? *) -> false
   | Await _ -> false
   | Spread _ -> false
 
diff --git a/compiler/core/js_exp_make.ml b/compiler/core/js_exp_make.ml
index 0dfc0166d9..1310675f56 100644
--- a/compiler/core/js_exp_make.ml
+++ b/compiler/core/js_exp_make.ml
@@ -696,13 +696,13 @@ let rec push_negation (e : t) : t option =
   | _ -> None
 
 (**
-  [simplify_and e1 e2] attempts to simplify the boolean AND expression [e1 && e2].
+  [simplify_and_ e1 e2] attempts to simplify the boolean AND expression [e1 && e2].
   Returns [Some simplified] if simplification is possible, [None] otherwise.
 
   Basic simplification rules:
   - [false && e] -> [false]
   - [true && e] -> [e] 
-  - [e && false] -> [false] If [e] has no side effects
+  - [e && false] -> [false]
   - [e && true] -> [e]
   - [(a && b) && e] -> If either [a && e] or [b && e] can be simplified, 
                        creates new AND expression with simplified parts: [(a' && b')]
@@ -735,7 +735,7 @@ let rec push_negation (e : t) : t option =
   attempting to reduce it to a simpler form. If no simplification is possible,
   returns [None].
 *)
-let rec simplify_and ~n (e1 : t) (e2 : t) : t option =
+let rec simplify_and_ ~n (e1 : t) (e2 : t) : t option =
   if debug then
     Printf.eprintf "%s simplify_and %s %s\n"
       (String.make (n * 2) ' ')
@@ -743,34 +743,34 @@ let rec simplify_and ~n (e1 : t) (e2 : t) : t option =
   let res =
     match (e1.expression_desc, e2.expression_desc) with
     | Bool false, _ -> Some false_
-    | _, Bool false when no_side_effect e1 -> Some false_
+    | _, Bool false -> Some false_
     | Bool true, _ -> Some e2
     | _, Bool true -> Some e1
     | Bin (And, a, b), _ -> (
-      let ao = simplify_and ~n:(n + 1) a e2 in
-      let bo = simplify_and ~n:(n + 1) b e2 in
+      let ao = simplify_and_ ~n:(n + 1) a e2 in
+      let bo = simplify_and_ ~n:(n + 1) b e2 in
       match (ao, bo) with
       | None, None -> (
-        match simplify_and ~n:(n + 1) a b with
+        match simplify_and_ ~n:(n + 1) a b with
         | None -> None
         | Some e -> simplify_and_force ~n:(n + 1) e e2)
       | Some a_, None -> simplify_and_force ~n:(n + 1) a_ b
       | None, Some b_ -> simplify_and_force ~n:(n + 1) a b_
       | Some a_, Some b_ -> simplify_and_force ~n:(n + 1) a_ b_)
     | _, Bin (And, a, b) ->
-      simplify_and ~n:(n + 1)
+      simplify_and_ ~n:(n + 1)
         {expression_desc = Bin (And, e1, a); comment = None}
         b
     | Bin (Or, a, b), _ -> (
-      let ao = simplify_and ~n:(n + 1) a e2 in
-      let bo = simplify_and ~n:(n + 1) b e2 in
+      let ao = simplify_and_ ~n:(n + 1) a e2 in
+      let bo = simplify_and_ ~n:(n + 1) b e2 in
       match (ao, bo) with
       | Some {expression_desc = Bool false}, None ->
         Some {expression_desc = Bin (And, b, e2); comment = None}
       | None, Some {expression_desc = Bool false} ->
         Some {expression_desc = Bin (And, a, e2); comment = None}
       | None, _ | _, None -> (
-        match simplify_or ~n:(n + 1) a b with
+        match simplify_or_ ~n:(n + 1) a b with
         | None -> None
         | Some e -> simplify_and_force ~n:(n + 1) e e2)
       | Some a_, Some b_ -> simplify_or_force ~n:(n + 1) a_ b_)
@@ -1037,12 +1037,12 @@ let rec simplify_and ~n (e1 : t) (e2 : t) : t option =
   res
 
 and simplify_and_force ~n (e1 : t) (e2 : t) : t option =
-  match simplify_and ~n e1 e2 with
+  match simplify_and_ ~n e1 e2 with
   | None -> Some {expression_desc = Bin (And, e1, e2); comment = None}
   | x -> x
 
 (**
-  [simplify_or e1 e2] attempts to simplify the boolean OR expression [e1 || e2].
+  [simplify_or_ e1 e2] attempts to simplify the boolean OR expression [e1 || e2].
   Returns [Some simplified] if simplification is possible, [None] otherwise.
 
   Basic simplification rules:
@@ -1061,7 +1061,7 @@ and simplify_and_force ~n (e1 : t) (e2 : t) : t option =
   This transformation allows reuse of [simplify_and]'s more extensive optimizations
   in the context of OR expressions.
 *)
-and simplify_or ~n (e1 : t) (e2 : t) : t option =
+and simplify_or_ ~n (e1 : t) (e2 : t) : t option =
   if debug then
     Printf.eprintf "%ssimplify_or %s %s\n"
       (String.make (n * 2) ' ')
@@ -1076,7 +1076,7 @@ and simplify_or ~n (e1 : t) (e2 : t) : t option =
     | _ -> (
       match (push_negation e1, push_negation e2) with
       | Some e1_, Some e2_ -> (
-        match simplify_and ~n:(n + 1) e1_ e2_ with
+        match simplify_and_ ~n:(n + 1) e1_ e2_ with
         | Some e -> push_negation e
         | None -> None)
       | _ -> None)
@@ -1091,10 +1091,18 @@ and simplify_or ~n (e1 : t) (e2 : t) : t option =
   res
 
 and simplify_or_force ~n (e1 : t) (e2 : t) : t option =
-  match simplify_or ~n e1 e2 with
+  match simplify_or_ ~n e1 e2 with
   | None -> Some {expression_desc = Bin (Or, e1, e2); comment = None}
   | x -> x
 
+let simplify_and (e1 : t) (e2 : t) : t option =
+  if no_side_effect e1 && no_side_effect e2 then simplify_and_ ~n:0 e1 e2
+  else None
+
+let simplify_or (e1 : t) (e2 : t) : t option =
+  if no_side_effect e1 && no_side_effect e2 then simplify_or_ ~n:0 e1 e2
+  else None
+
 let and_ ?comment (e1 : t) (e2 : t) : t =
   match (e1.expression_desc, e2.expression_desc) with
   | Var i, Var j when Js_op_util.same_vident i j -> e1
@@ -1111,7 +1119,7 @@ let and_ ?comment (e1 : t) (e2 : t) : t =
     when Js_op_util.same_vident i j ->
     e2
   | _, _ -> (
-    match simplify_and ~n:0 e1 e2 with
+    match simplify_and e1 e2 with
     | Some e -> e
     | None -> {expression_desc = Bin (And, e1, e2); comment})
 
@@ -1125,7 +1133,7 @@ let or_ ?comment (e1 : t) (e2 : t) =
     when Js_op_util.same_vident i j ->
     {e2 with expression_desc = Bin (Or, r, l)}
   | _, _ -> (
-    match simplify_or ~n:0 e1 e2 with
+    match simplify_or e1 e2 with
     | Some e -> e
     | None -> {expression_desc = Bin (Or, e1, e2); comment})
 
@@ -1190,11 +1198,11 @@ let rec econd ?comment (pred : t) (ifso : t) (ifnot : t) : t =
       Seq (b, {expression_desc = Undefined _}) ) ->
     seq (econd ?comment pred a b) undefined
   | _, _, Bool false -> (
-    match simplify_and ~n:0 pred ifso with
+    match simplify_and pred ifso with
     | Some e -> e
     | None -> default ())
   | _, Bool false, _ -> (
-    match simplify_and ~n:0 (not pred) ifnot with
+    match simplify_and (not pred) ifnot with
     | Some e -> e
     | None -> default ())
   | _ -> default ()
diff --git a/tests/tests/src/option_repr_test.mjs b/tests/tests/src/option_repr_test.mjs
index 9f4d0e742b..d67be245ef 100644
--- a/tests/tests/src/option_repr_test.mjs
+++ b/tests/tests/src/option_repr_test.mjs
@@ -221,9 +221,9 @@ b("File \"option_repr_test.res\", line 127, characters 3-10", Belt_List.every(xs
 let xs_1$1 = {
   hd: neqx(undefined, null),
   tl: {
-    hd: Primitive_object.equal(Primitive_option.some(undefined), Primitive_option.some(undefined)),
+    hd: Primitive_object.equal(Primitive_option.some(undefined), Primitive_option.some(undefined)) && Primitive_object.equal(Primitive_option.some(undefined), Primitive_option.some(undefined)),
     tl: {
-      hd: Primitive_object.equal(Primitive_option.some(Primitive_option.some(undefined)), Primitive_option.some(Primitive_option.some(undefined))),
+      hd: Primitive_object.equal(Primitive_option.some(Primitive_option.some(undefined)), Primitive_option.some(Primitive_option.some(undefined))) && Primitive_object.equal(Primitive_option.some(Primitive_option.some(undefined)), Primitive_option.some(Primitive_option.some(undefined))),
       tl: {
         hd: Primitive_object.notequal(Primitive_option.some(Primitive_option.some(Primitive_option.some(undefined))), Primitive_option.some(Primitive_option.some(undefined))) && Primitive_object.notequal(Primitive_option.some(Primitive_option.some(undefined)), Primitive_option.some(Primitive_option.some(Primitive_option.some(undefined)))),
         tl: /* [] */0

From c0e5b7843b5ece3d3cf39a7e577b5e99c0deb544 Mon Sep 17 00:00:00 2001
From: Cristiano Calcagno <cristianoc@users.noreply.github.com>
Date: Sun, 10 Nov 2024 08:57:41 +0100
Subject: [PATCH 06/10] More side effects.

---
 compiler/core/js_exp_make.ml           | 26 ++++++++++++++++++--------
 compiler/core/js_exp_make.mli          |  2 +-
 compiler/core/lam_compile_primitive.ml |  8 ++++----
 3 files changed, 23 insertions(+), 13 deletions(-)

diff --git a/compiler/core/js_exp_make.ml b/compiler/core/js_exp_make.ml
index 1310675f56..893753b761 100644
--- a/compiler/core/js_exp_make.ml
+++ b/compiler/core/js_exp_make.ml
@@ -1394,13 +1394,15 @@ let rec int_comp (cmp : Lam_compat.comparison) ?comment (e0 : t) (e1 : t) =
           _ ),
       Number (Int {i = 0l}) ) ->
     int_comp cmp l r (* = 0 > 0 < 0 *)
-  | Ceq, Optional_block _, Undefined _ | Ceq, Undefined _, Optional_block _ ->
+  | (Ceq, Optional_block _, Undefined _ | Ceq, Undefined _, Optional_block _)
+    when no_side_effect e0 && no_side_effect e1 ->
     false_
   | Ceq, _, _ -> int_equal e0 e1
   | Cneq, Optional_block _, Undefined _
   | Cneq, Undefined _, Optional_block _
   | Cneq, Caml_block _, Number _
-  | Cneq, Number _, Caml_block _ ->
+  | Cneq, Number _, Caml_block _
+    when no_side_effect e0 && no_side_effect e1 ->
     true_
   | _ -> bin ?comment (Lam_compile_util.jsop_of_comp cmp) e0 e1
 
@@ -1718,7 +1720,7 @@ let of_block ?comment ?e block : t =
 let is_null ?comment (x : t) = triple_equal ?comment x nil
 let is_undef ?comment x = triple_equal ?comment x undefined
 
-let for_sure_js_null_undefined (x : t) =
+let is_null_undefined_constant (x : t) =
   match x.expression_desc with
   | Null | Undefined _ -> true
   | _ -> false
@@ -1730,28 +1732,36 @@ let is_null_undefined ?comment (x : t) : t =
   | _ -> {comment; expression_desc = Is_null_or_undefined x}
 
 let eq_null_undefined_boolean ?comment (a : t) (b : t) =
+  (* [a == b] when either a or b is null or undefined *)
   match (a.expression_desc, b.expression_desc) with
   | ( (Null | Undefined _),
-      (Bool _ | Number _ | Typeof _ | Fun _ | Array _ | Caml_block _) ) ->
+      (Bool _ | Number _ | Typeof _ | Fun _ | Array _ | Caml_block _) )
+    when no_side_effect b ->
     false_
   | ( (Bool _ | Number _ | Typeof _ | Fun _ | Array _ | Caml_block _),
-      (Null | Undefined _) ) ->
+      (Null | Undefined _) )
+    when no_side_effect a ->
     false_
   | Null, Undefined _ | Undefined _, Null -> false_
   | Null, Null | Undefined _, Undefined _ -> true_
   | _ -> {expression_desc = Bin (EqEqEq, a, b); comment}
 
 let neq_null_undefined_boolean ?comment (a : t) (b : t) =
+  (* [a != b] when either a or b is null or undefined *)
   match (a.expression_desc, b.expression_desc) with
   | ( (Null | Undefined _),
-      (Bool _ | Number _ | Typeof _ | Fun _ | Array _ | Caml_block _) ) ->
+      (Bool _ | Number _ | Typeof _ | Fun _ | Array _ | Caml_block _) )
+    when no_side_effect b ->
     true_
   | ( (Bool _ | Number _ | Typeof _ | Fun _ | Array _ | Caml_block _),
-      (Null | Undefined _) ) ->
+      (Null | Undefined _) )
+    when no_side_effect a ->
     true_
   | Null, Null | Undefined _, Undefined _ -> false_
   | Null, Undefined _ | Undefined _, Null -> true_
-  | _ -> {expression_desc = Bin (NotEqEq, a, b); comment}
+  | _ ->
+    let _ = assert false in
+    {expression_desc = Bin (NotEqEq, a, b); comment}
 
 let make_exception (s : string) =
   pure_runtime_call Primitive_modules.exceptions Literals.create [str s]
diff --git a/compiler/core/js_exp_make.mli b/compiler/core/js_exp_make.mli
index e890e4c6aa..20022f942c 100644
--- a/compiler/core/js_exp_make.mli
+++ b/compiler/core/js_exp_make.mli
@@ -365,7 +365,7 @@ val is_null : ?comment:string -> t -> t
 
 val is_undef : ?comment:string -> t -> t
 
-val for_sure_js_null_undefined : J.expression -> bool
+val is_null_undefined_constant : J.expression -> bool
 
 val is_null_undefined : ?comment:string -> t -> t
 
diff --git a/compiler/core/lam_compile_primitive.ml b/compiler/core/lam_compile_primitive.ml
index efea6c977b..47c255afb2 100644
--- a/compiler/core/lam_compile_primitive.ml
+++ b/compiler/core/lam_compile_primitive.ml
@@ -373,13 +373,13 @@ let translate output_prefix loc (cxt : Lam_compile_context.t)
     match args with
     | [e1; e2]
       when cmp = Ceq
-           && (E.for_sure_js_null_undefined e1
-              || E.for_sure_js_null_undefined e2) ->
+           && (E.is_null_undefined_constant e1
+              || E.is_null_undefined_constant e2) ->
       E.eq_null_undefined_boolean e1 e2
     | [e1; e2]
       when cmp = Cneq
-           && (E.for_sure_js_null_undefined e1
-              || E.for_sure_js_null_undefined e2) ->
+           && (E.is_null_undefined_constant e1
+              || E.is_null_undefined_constant e2) ->
       E.neq_null_undefined_boolean e1 e2
     | [e1; e2] ->
       Location.prerr_warning loc Warnings.Bs_polymorphic_comparison;

From 00b9b92cb9df0642d3371f754fe2dbcd3478360f Mon Sep 17 00:00:00 2001
From: Cristiano Calcagno <cristianoc@users.noreply.github.com>
Date: Sun, 10 Nov 2024 09:38:24 +0100
Subject: [PATCH 07/10] More side effect cases.

---
 compiler/core/js_exp_make.ml | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/compiler/core/js_exp_make.ml b/compiler/core/js_exp_make.ml
index 893753b761..e894d761dd 100644
--- a/compiler/core/js_exp_make.ml
+++ b/compiler/core/js_exp_make.ml
@@ -559,7 +559,8 @@ let string_length ?comment (e : t) : t =
 (* TODO: use [Buffer] instead? *)
 let bytes_length ?comment (e : t) : t =
   match e.expression_desc with
-  | Array (l, _) -> int ?comment (Int32.of_int (List.length l))
+  | Array (l, _) when no_side_effect e ->
+    int ?comment (Int32.of_int (List.length l))
   | _ -> {expression_desc = Length (e, Bytes); comment}
 
 let function_length ?comment (e : t) : t =
@@ -624,7 +625,8 @@ let rec triple_equal ?comment (e0 : t) (e1 : t) : t =
   | Undefined _, Optional_block _
   | Optional_block _, Undefined _
   | Null, Undefined _
-  | Undefined _, Null ->
+  | Undefined _, Null
+    when no_side_effect e0 && no_side_effect e1 ->
     false_
   | Null, Null | Undefined _, Undefined _ -> true_
   | _ -> {expression_desc = Bin (EqEqEq, e0, e1); comment}
@@ -1604,11 +1606,9 @@ let is_pos_pow n =
 
 let int32_mul ?comment (e1 : J.expression) (e2 : J.expression) : J.expression =
   match (e1, e2) with
-  | {expression_desc = Number (Int {i = 0l}); _}, x
-    when Js_analyzer.no_side_effect_expression x ->
+  | {expression_desc = Number (Int {i = 0l}); _}, x when no_side_effect x ->
     zero_int_literal
-  | x, {expression_desc = Number (Int {i = 0l}); _}
-    when Js_analyzer.no_side_effect_expression x ->
+  | x, {expression_desc = Number (Int {i = 0l}); _} when no_side_effect x ->
     zero_int_literal
   | ( {expression_desc = Number (Int {i = i0}); _},
       {expression_desc = Number (Int {i = i1}); _} ) ->

From 90f7e9bb7bbf4b958c3726a6003aa28ca3c8d524 Mon Sep 17 00:00:00 2001
From: Cristiano Calcagno <cristianoc@users.noreply.github.com>
Date: Sun, 10 Nov 2024 09:45:44 +0100
Subject: [PATCH 08/10] dead code

---
 compiler/core/js_exp_make.ml  | 7 -------
 compiler/core/js_exp_make.mli | 2 --
 2 files changed, 9 deletions(-)

diff --git a/compiler/core/js_exp_make.ml b/compiler/core/js_exp_make.ml
index e894d761dd..652f1d844d 100644
--- a/compiler/core/js_exp_make.ml
+++ b/compiler/core/js_exp_make.ml
@@ -556,13 +556,6 @@ let string_length ?comment (e : t) : t =
   (* No optimization for {j||j}*)
   | _ -> {expression_desc = Length (e, String); comment}
 
-(* TODO: use [Buffer] instead? *)
-let bytes_length ?comment (e : t) : t =
-  match e.expression_desc with
-  | Array (l, _) when no_side_effect e ->
-    int ?comment (Int32.of_int (List.length l))
-  | _ -> {expression_desc = Length (e, Bytes); comment}
-
 let function_length ?comment (e : t) : t =
   match e.expression_desc with
   | Fun {is_method; params} ->
diff --git a/compiler/core/js_exp_make.mli b/compiler/core/js_exp_make.mli
index 20022f942c..f8216e1acb 100644
--- a/compiler/core/js_exp_make.mli
+++ b/compiler/core/js_exp_make.mli
@@ -143,8 +143,6 @@ val array_length : ?comment:string -> t -> t
 
 val string_length : ?comment:string -> t -> t
 
-val bytes_length : ?comment:string -> t -> t
-
 val function_length : ?comment:string -> t -> t
 
 val string_append : ?comment:string -> t -> t -> t

From 1a5f2865feaff297d1c6eca4acfca8c2d75d8894 Mon Sep 17 00:00:00 2001
From: Cristiano Calcagno <cristianoc@users.noreply.github.com>
Date: Sun, 10 Nov 2024 09:51:10 +0100
Subject: [PATCH 09/10] Add example of what was previously over-optimized.

---
 tests/tests/src/Equality_over_optimization.mjs | 9 +++++++++
 tests/tests/src/Equality_over_optimization.res | 1 +
 2 files changed, 10 insertions(+)
 create mode 100644 tests/tests/src/Equality_over_optimization.mjs
 create mode 100644 tests/tests/src/Equality_over_optimization.res

diff --git a/tests/tests/src/Equality_over_optimization.mjs b/tests/tests/src/Equality_over_optimization.mjs
new file mode 100644
index 0000000000..a9b38bff6e
--- /dev/null
+++ b/tests/tests/src/Equality_over_optimization.mjs
@@ -0,0 +1,9 @@
+// Generated by ReScript, PLEASE EDIT WITH CARE
+
+
+let z = undefined === [(console.log("hello"), undefined)];
+
+export {
+  z,
+}
+/* z Not a pure module */
diff --git a/tests/tests/src/Equality_over_optimization.res b/tests/tests/src/Equality_over_optimization.res
new file mode 100644
index 0000000000..a6bc04a918
--- /dev/null
+++ b/tests/tests/src/Equality_over_optimization.res
@@ -0,0 +1 @@
+let z = None == Some([Console.log("hello")])

From 6d4c212ab0900d8705a6f9c0ae6274d77de88ca3 Mon Sep 17 00:00:00 2001
From: Cristiano Calcagno <cristianoc@users.noreply.github.com>
Date: Sun, 10 Nov 2024 09:58:05 +0100
Subject: [PATCH 10/10] Update CHANGELOG.md

---
 CHANGELOG.md | 23 ++++++++++++++---------
 1 file changed, 14 insertions(+), 9 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 6c5ad614c5..45e8ef2753 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -16,6 +16,20 @@
 
 - Introduce "Unified operators" for arithmetic operators (`+`, `-`, `*`, `/`, `mod`). See https://github.com/rescript-lang/rescript-compiler/pull/7057
 
+
+#### :bug: Bug fix
+- Fix and clean up boolean and/or optimizations. https://github.com/rescript-lang/rescript-compiler/pull/7134 https://github.com/rescript-lang/rescript-compiler/pull/7151
+
+#### :nail_care: Polish
+- Improve code generation for pattern matching of untagged variants. https://github.com/rescript-lang/rescript-compiler/pull/7128
+- Improve negation handling in combination with and/or to simplify generated code (especially coming out of pattern matching). https://github.com/rescript-lang/rescript-compiler/pull/7138
+- optimize JavaScript code generation by using x == null checks and improving type-based optimizations for string/number literals. https://github.com/rescript-lang/rescript-compiler/pull/7141
+- Improve pattern matching on optional fields. https://github.com/rescript-lang/rescript-compiler/pull/7143 https://github.com/rescript-lang/rescript-compiler/pull/7144
+- Optimize compilation of switch statements for untagged variants when there are no literal cases. https://github.com/rescript-lang/rescript-compiler/pull/7135
+- Further improve boolean optimizations. https://github.com/rescript-lang/rescript-compiler/pull/7149
+- Simplify code generated for conditionals. https://github.com/rescript-lang/rescript-compiler/pull/7151
+
+
 # 12.0.0-alpha.4
 
 #### :boom: Breaking Change
@@ -44,10 +58,8 @@
 - Fix variant cast to int. https://github.com/rescript-lang/rescript-compiler/pull/7058
 - Fix comments formatted away in function without arguments. https://github.com/rescript-lang/rescript-compiler/pull/7095
 - Fix genType JSX component compilation. https://github.com/rescript-lang/rescript-compiler/pull/7107
-- Fix and clean up boolean and/or optimizations. https://github.com/rescript-lang/rescript-compiler/pull/7134
 
 #### :nail_care: Polish
-
 - Add some context to error message for unused variables. https://github.com/rescript-lang/rescript-compiler/pull/7050
 - Improve error message when passing `children` prop to a component that doesn't accept it. https://github.com/rescript-lang/rescript-compiler/pull/7044
 - Improve error messages for pattern matching on option vs non-option, and vice versa. https://github.com/rescript-lang/rescript-compiler/pull/7035
@@ -57,13 +69,6 @@
 - 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
-- Improve negation handling in combination with and/or to simplify generated code (especially coming out of pattern matching). https://github.com/rescript-lang/rescript-compiler/pull/7138
-- optimize JavaScript code generation by using x == null checks and improving type-based optimizations for string/number literals. https://github.com/rescript-lang/rescript-compiler/pull/7141
-- Improve pattern matching on optional fields. https://github.com/rescript-lang/rescript-compiler/pull/7143 https://github.com/rescript-lang/rescript-compiler/pull/7144
-- Optimize compilation of switch statements for untagged variants when there are no literal cases. https://github.com/rescript-lang/rescript-compiler/pull/7135
-- Further improve boolean optimizations. https://github.com/rescript-lang/rescript-compiler/pull/7149
-- Simplify code generated forconditionals. https://github.com/rescript-lang/rescript-compiler/pull/7151
 
 
 #### :house: Internal