[clang-tools-extra] [clang-tidy] Allow type-generic builtins in pro-type-vararg check (PR #178656)

[via cfe-commits]

https://github.com/mugiwaraluffy56 updated https://github.com/llvm/llvm-project/pull/178656

>From 5227669582c0704743b2b6d3ea10f062272dfcc1 Mon Sep 17 00:00:00 2001
From: mugiwaraluffy56 <myakampuneeth at gmail.com>
Date: Thu, 29 Jan 2026 19:22:00 +0530
Subject: [PATCH] [clang-tidy] Allow type-generic builtins in pro-type-vararg
 check

Add __builtin_clzg, __builtin_ctzg, __builtin_popcountg, and
__builtin_bswapg to the allowed variadics list. These type-generic
builtins are declared as variadic to accept any integer type, but
they are not C-style vararg functions and should not trigger the
hicpp-vararg / cppcoreguidelines-pro-type-vararg warning.

Fixes #178629
---
 .../clang-tidy/cppcoreguidelines/ProTypeVarargCheck.cpp  | 9 +++++++++
 clang-tools-extra/docs/ReleaseNotes.rst                  | 6 ++++++
 .../checkers/cppcoreguidelines/pro-type-vararg.cpp       | 6 ++++++
 3 files changed, 21 insertions(+)

diff --git a/clang-tools-extra/clang-tidy/cppcoreguidelines/ProTypeVarargCheck.cpp b/clang-tools-extra/clang-tidy/cppcoreguidelines/ProTypeVarargCheck.cpp
index d5ff4af84b0b7..7c4286d410d36 100644
--- a/clang-tools-extra/clang-tidy/cppcoreguidelines/ProTypeVarargCheck.cpp
+++ b/clang-tools-extra/clang-tidy/cppcoreguidelines/ProTypeVarargCheck.cpp
@@ -178,6 +178,15 @@ void ProTypeVarargCheck::check(const MatchFinder::MatchResult &Result) {
   if (const auto *Matched = Result.Nodes.getNodeAs<CallExpr>("callvararg")) {
     if (hasSingleVariadicArgumentWithValue(Matched, 0))
       return;
+
+    // Skip builtins with custom type checking - they use variadics as an
+    // implementation detail to accept multiple types, not for C-style varargs.
+    if (const auto *FD = Matched->getDirectCallee())
+      if (const unsigned BuiltinID = FD->getBuiltinID();
+          BuiltinID &&
+          Result.Context->BuiltinInfo.hasCustomTypechecking(BuiltinID))
+        return;
+
     diag(Matched->getExprLoc(), "do not call c-style vararg functions");
   }
 
diff --git a/clang-tools-extra/docs/ReleaseNotes.rst b/clang-tools-extra/docs/ReleaseNotes.rst
index 754880bd1a381..082117452b2ff 100644
--- a/clang-tools-extra/docs/ReleaseNotes.rst
+++ b/clang-tools-extra/docs/ReleaseNotes.rst
@@ -136,6 +136,12 @@ Changes in existing checks
   the invalidating function in the warning message when a custom invalidation
   function is used (via the `InvalidationFunctions` option).
 
+- Improved :doc:`cppcoreguidelines-pro-type-vararg
+  <clang-tidy/checks/cppcoreguidelines/pro-type-vararg>` check by no longer
+  warning on builtins with custom type checking (e.g., type-generic builtins
+  like ``__builtin_clzg``) that use variadic declarations as an implementation
+  detail.
+
 - Improved :doc:`llvm-use-ranges
   <clang-tidy/checks/llvm/use-ranges>` check by adding support for the following
   algorithms: ``std::accumulate``, ``std::replace_copy``, and
diff --git a/clang-tools-extra/test/clang-tidy/checkers/cppcoreguidelines/pro-type-vararg.cpp b/clang-tools-extra/test/clang-tidy/checkers/cppcoreguidelines/pro-type-vararg.cpp
index 3f73d1de333f4..1a5a5fb7dd93c 100644
--- a/clang-tools-extra/test/clang-tidy/checkers/cppcoreguidelines/pro-type-vararg.cpp
+++ b/clang-tools-extra/test/clang-tidy/checkers/cppcoreguidelines/pro-type-vararg.cpp
@@ -57,6 +57,12 @@ void ignoredBuiltinsTest(void *ptr) {
   (void)__builtin_fpclassify(0, 0, 0, 0, 0, 0.f);
   (void)__builtin_isinf_sign(0.f);
   (void)__builtin_prefetch(nullptr);
+
+  // GH#178629: Type-generic builtins should not warn.
+  (void)__builtin_clzg(1u);
+  (void)__builtin_ctzg(1u);
+  (void)__builtin_popcountg(1u);
+  (void)__builtin_bswapg(1u);
 }
 
 // Some implementations of __builtin_va_list and __builtin_ms_va_list desugared