From 3ed2fffa0bd6d4eb771b4a630bdeade72950c1fc Mon Sep 17 00:00:00 2001
From: Thomas Weber <weber_t@mailbox.org>
Date: Wed, 9 Sep 2020 21:38:54 -0500
Subject: [PATCH] js: Optimize op.equals when comparing against a constant 0

---
 src/compiler/jsgen.js | 31 +++++--------------------------
 1 file changed, 5 insertions(+), 26 deletions(-)

diff --git a/src/compiler/jsgen.js b/src/compiler/jsgen.js
index 70ef6ced..ef975dea 100644
--- a/src/compiler/jsgen.js
+++ b/src/compiler/jsgen.js
@@ -174,26 +174,6 @@ disableToString(TypedInput.prototype.asString);
 disableToString(TypedInput.prototype.asBoolean);
 disableToString(TypedInput.prototype.asUnknown);
 
-/**
- * @param {Input} input The input to examine.
- * @returns {input is ConstantInput} true if the input is a ConstantInput or subclass of ConstantInput
- */
-// @ts-expect-error
-const isConstantInput = input => typeof input.constantValue !== 'undefined';
-
-/**
- * Determine if an input is a constant that is a non-zero number.
- * @param {Input} input The input to examine.
- * @returns {boolean} true if the input is a constant non-zero number
- */
-const isNonZeroNumberConstant = input => {
-    if (!isConstantInput(input)) {
-        return false;
-    }
-    const value = +input.constantValue;
-    return value !== 0;
-};
-
 class JSGenerator {
     constructor (script, ast, target) {
         this.script = script;
@@ -307,14 +287,13 @@ class JSGenerator {
             if (leftAlwaysNumber && rightAlwaysNumber) {
                 return new TypedInput(`(${left.asNumber()} === ${right.asNumber()})`, TYPE_BOOLEAN);
             }
-            // When one operand is known to be a non-zero constant, we can use ===
-            // 0 is not allowed here as NaN will get converted to zero, and "apple or any other NaN value = 0" should not return true.
+            // When one operand is known to be a number constant, we can use ===
             // todo: this might be unsafe
-            if (leftAlwaysNumber && isNonZeroNumberConstant(left)) {
-                return new TypedInput(`(${left.asNumber()} === ${right.asNumber()})`, TYPE_BOOLEAN);
+            if (leftAlwaysNumber && left instanceof ConstantInput) {
+                return new TypedInput(`(${left.asNumber()} === ${right.asNumberOrNaN()})`, TYPE_BOOLEAN);
             }
-            if (rightAlwaysNumber && isNonZeroNumberConstant(right)) {
-                return new TypedInput(`(${left.asNumber()} === ${right.asNumber()})`, TYPE_BOOLEAN);
+            if (rightAlwaysNumber && right instanceof ConstantInput) {
+                return new TypedInput(`(${left.asNumberOrNaN()} === ${right.asNumber()})`, TYPE_BOOLEAN);
             }
             // No compile-time optimizations possible - use fallback method.
             return new TypedInput(`compareEqual(${left.asUnknown()}, ${right.asUnknown()})`, TYPE_BOOLEAN);