From faf7bdf87e729080db2fa5b5a77bed92c6abfd46 Mon Sep 17 00:00:00 2001
From: Sam Clegg <sbc@chromium.org>
Date: Fri, 6 Nov 2026 18:01:48 -0800
Subject: [PATCH] Optimize `compiler.mjs` for `__const` dependencies and
 `isDecorator`

Since #28144, every C define in `struct_info.json` is added to
`LibraryManager.library` as three entries (`$FOO`, `$FOO__const`, and
`$FOO__internal`). Adding hundreds more constants to `struct_info.json`
(as in #28199) would otherwise incur two compile-time performance costs
in `compiler.mjs`:

1. In `--symbols-only` mode we only need to discover transitive
   dependencies on native symbols. As JS library functions replace magic
   numbers with `struct_info.json` constants, `addImplicitDeps`
   (`src/jsifier.mjs`) would otherwise record every referenced constant
   in `__deps` and repeatedly traverse them in `getTransitiveDeps`.
   Skipping `__const` symbols in `--symbols-only` mode avoids this work.

2. Each `struct_info.json` constant adds three keys to
   `LibraryManager.library`, which is iterated over in multiple passes
   that call `isDecorator` (`src/utility.mjs`) on every key. Using
   `lastIndexOf('__')` and a `Set` lookup instead of
   `decoratorSuffixes.some` with `endsWith` avoids scanning all 15
   decorator suffixes for every key in the library.

See: #28199
---
 src/jsifier.mjs | 1 +
 src/utility.mjs | 5 ++++-
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/src/jsifier.mjs b/src/jsifier.mjs
index 92ad005490559..c5856a40bc5d8 100644
--- a/src/jsifier.mjs
+++ b/src/jsifier.mjs
@@ -784,6 +784,7 @@ function(${args}) {
       function addImplicitDeps(snippet) {
         for (const dep of calcImplicitDeps(snippet)) {
           if (dep === symbol) continue;
+          if (symbolsOnly && LibraryManager.library[dep + '__const']) continue;
           if (explicitDeps.has(dep)) {
             if (!symbolsOnly && (STRICT || !isUserSymbol) && LibraryManager.library[symbol] !== dep) {
               warn(`${symbol}: redundant __deps entry: ${dep}`);
diff --git a/src/utility.mjs b/src/utility.mjs
index c8ee6f5d4397d..f2ffa07459611 100644
--- a/src/utility.mjs
+++ b/src/utility.mjs
@@ -227,8 +227,11 @@ export const decoratorSuffixes = [
   '__const',
 ];
 
+const decoratorSuffixSet = new Set(decoratorSuffixes);
+
 export function isDecorator(ident) {
-  return decoratorSuffixes.some((suffix) => ident.endsWith(suffix));
+  const index = ident.lastIndexOf('__');
+  return index > 0 && decoratorSuffixSet.has(ident.slice(index));
 }
 
 export function defineConsts(consts) {