[clang] [clang][Diagnostics] Only record lexer check points when colors are enabled (PR #204926)

[via cfe-commits]

https://github.com/AnonMiraj created https://github.com/llvm/llvm-project/pull/204926

Only build lexer check points when colored diagnostics are enabled, since that's the only case where they're ever used,
This should reduce the cost on larger builds.

| Commit | Basket Ir | Delta |
|---|---|---|
| 863b2c84 (Parent) | 30,240,576,150 | — |
| 718aac9f (Commit) | 30,336,607,185 | +0.318% |
| **+ this pr** | **30,279,772,621** | **+0.130%** |


**synthetic error file (12.3k lines, 300 errors):**

| Build | Error-TU Ir (colors on) | Δ vs commit |
|---|---|---|
| 718aac9f (Commit) | 1,386,488,658 | — |
| **+ this pr** | **1,387,140,588** | **+0.05%** |

Resolves #203764 

>From 6f15db3e1232d7f18f6732a1338960b3aa22b49e Mon Sep 17 00:00:00 2001
From: Anonmiraj <ezzibrahimx at gmail.com>
Date: Sat, 20 Jun 2026 14:41:32 +0300
Subject: [PATCH] [clang][Diagnostics] Only record lexer check points when
 colors are enabled

---
 clang/include/clang/Lex/Preprocessor.h | 3 +++
 clang/lib/Lex/Preprocessor.cpp         | 6 +++++-
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/clang/include/clang/Lex/Preprocessor.h b/clang/include/clang/Lex/Preprocessor.h
index 8b684e85eb1c1..9f592892f9218 100644
--- a/clang/include/clang/Lex/Preprocessor.h
+++ b/clang/include/clang/Lex/Preprocessor.h
@@ -381,6 +381,9 @@ class Preprocessor {
   llvm::DenseMap<FileID, SmallVector<const char *>> CheckPoints;
   unsigned CheckPointCounter = 0;
 
+  /// Whether to record lexer check points for diagnostic snippet highlighting.
+  bool RecordCheckPoints = false;
+
   /// Whether we're importing a standard C++20 named Modules.
   bool ImportingCXXNamedModules = false;
 
diff --git a/clang/lib/Lex/Preprocessor.cpp b/clang/lib/Lex/Preprocessor.cpp
index 1e21b4a94cea3..f58d8589c1afd 100644
--- a/clang/lib/Lex/Preprocessor.cpp
+++ b/clang/lib/Lex/Preprocessor.cpp
@@ -101,6 +101,9 @@ Preprocessor::Preprocessor(const PreprocessorOptions &PPOpts,
       CurSubmoduleState(&NullSubmoduleState) {
   OwnsHeaderSearch = OwnsHeaders;
 
+  // Only record check points if we might highlight diagnostic snippets.
+  RecordCheckPoints = getDiagnostics().getDiagnosticOptions().ShowColors;
+
   // Default to discarding comments.
   KeepComments = false;
   KeepMacroComments = false;
@@ -1011,7 +1014,8 @@ void Preprocessor::Lex(Token &Result) {
     }
   }
 
-  if (CurLexer && ++CheckPointCounter == CheckPointStepSize) {
+  if (RecordCheckPoints && CurLexer &&
+      ++CheckPointCounter == CheckPointStepSize) {
     CheckPoints[CurLexer->getFileID()].push_back(CurLexer->BufferPtr);
     CheckPointCounter = 0;
   }