[clang-tidy] Allow type-generic builtins in pro-type-vararg check #178656

mugiwaraluffy56 · 2026-01-29T13:53:03Z

Summary

Add type generic builtins to the allowed variadics list in the cppcoreguidelines-pro-type-vararg check (also used by hicpp-vararg):

__builtin_clzg
__builtin_ctzg
__builtin_popcountg
__builtin_bswapg

Root Cause

These builtins are declared as variadic (int(...)) to accept any integer type via CustomTypeChecking. However, they are not C style vararg functions , they take exactly one argument of a generic integer type.

Test

Added test cases in pro-type-vararg.cpp to verify no warning is emitted.

Fixes #178629

mugiwaraluffy56 · 2026-01-29T13:53:23Z

@PiotrZSL Could you please review this? This fixes a false positive for type generic builtins like __builtin_popcountg. Thanks!

llvmbot · 2026-01-29T13:53:37Z

@llvm/pr-subscribers-clang-tools-extra

Author: puneeth_aditya_5656 (mugiwaraluffy56)

Changes

Summary

Add type generic builtins to the allowed variadics list in the cppcoreguidelines-pro-type-vararg check (also used by hicpp-vararg):

__builtin_clzg
__builtin_ctzg
__builtin_popcountg
__builtin_bswapg

Root Cause

These builtins are declared as variadic (int(...)) to accept any integer type via CustomTypeChecking. However, they are not C style vararg functions , they take exactly one argument of a generic integer type.

Test

Added test cases in pro-type-vararg.cpp to verify no warning is emitted.

Fixes #17862

Full diff: https://github.com/llvm/llvm-project/pull/178656.diff

2 Files Affected:

(modified) clang-tools-extra/clang-tidy/cppcoreguidelines/ProTypeVarargCheck.cpp (+5)
(modified) clang-tools-extra/test/clang-tidy/checkers/cppcoreguidelines/pro-type-vararg.cpp (+6)

diff --git a/clang-tools-extra/clang-tidy/cppcoreguidelines/ProTypeVarargCheck.cpp b/clang-tools-extra/clang-tidy/cppcoreguidelines/ProTypeVarargCheck.cpp
index d5ff4af84b0b7..73cadfdf14614 100644
--- a/clang-tools-extra/clang-tidy/cppcoreguidelines/ProTypeVarargCheck.cpp
+++ b/clang-tools-extra/clang-tidy/cppcoreguidelines/ProTypeVarargCheck.cpp
@@ -56,6 +56,11 @@ static constexpr StringRef AllowedVariadics[] = {
     "__builtin_nontemporal_store",
     "__builtin_nontemporal_load",
     "__builtin_ms_va_start",
+    // Type-generic builtins: declared variadic to accept any integer type.
+    "__builtin_clzg",
+    "__builtin_ctzg",
+    "__builtin_popcountg",
+    "__builtin_bswapg",
     // clang-format on
 };
 
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

llvmbot · 2026-01-29T13:53:39Z

@llvm/pr-subscribers-clang-tidy

Author: puneeth_aditya_5656 (mugiwaraluffy56)

Changes

Summary

Add type generic builtins to the allowed variadics list in the cppcoreguidelines-pro-type-vararg check (also used by hicpp-vararg):

__builtin_clzg
__builtin_ctzg
__builtin_popcountg
__builtin_bswapg

Root Cause

These builtins are declared as variadic (int(...)) to accept any integer type via CustomTypeChecking. However, they are not C style vararg functions , they take exactly one argument of a generic integer type.

Test

Added test cases in pro-type-vararg.cpp to verify no warning is emitted.

Fixes #17862

Full diff: https://github.com/llvm/llvm-project/pull/178656.diff

2 Files Affected:

(modified) clang-tools-extra/clang-tidy/cppcoreguidelines/ProTypeVarargCheck.cpp (+5)
(modified) clang-tools-extra/test/clang-tidy/checkers/cppcoreguidelines/pro-type-vararg.cpp (+6)

diff --git a/clang-tools-extra/clang-tidy/cppcoreguidelines/ProTypeVarargCheck.cpp b/clang-tools-extra/clang-tidy/cppcoreguidelines/ProTypeVarargCheck.cpp
index d5ff4af84b0b7..73cadfdf14614 100644
--- a/clang-tools-extra/clang-tidy/cppcoreguidelines/ProTypeVarargCheck.cpp
+++ b/clang-tools-extra/clang-tidy/cppcoreguidelines/ProTypeVarargCheck.cpp
@@ -56,6 +56,11 @@ static constexpr StringRef AllowedVariadics[] = {
     "__builtin_nontemporal_store",
     "__builtin_nontemporal_load",
     "__builtin_ms_va_start",
+    // Type-generic builtins: declared variadic to accept any integer type.
+    "__builtin_clzg",
+    "__builtin_ctzg",
+    "__builtin_popcountg",
+    "__builtin_bswapg",
     // clang-format on
 };
 
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

zeyi2

Please add an entry in ReleaseNotes.rst :)

mugiwaraluffy56 · 2026-01-29T14:02:06Z

Please add an entry in ReleaseNotes.rst :)

Added the ReleaseNotes entry. Thanks for the review!

zeyi2

Overall LGTM, thank you!

But please wait for other reviewers :)

clang-tools-extra/test/clang-tidy/checkers/cppcoreguidelines/pro-type-vararg.cpp

localspook

Apart from the open comment, LGTM

efriedma-quic · 2026-01-29T21:40:52Z

clang-tools-extra/clang-tidy/cppcoreguidelines/ProTypeVarargCheck.cpp

+    "__builtin_clzg",
+    "__builtin_ctzg",
+    "__builtin_popcountg",
+    "__builtin_bswapg",


Can we just check hasCustomTypechecking() instead of listing out a bunch of builtins here? The fact that these builtins are "variadic" is an clang implementation detail, and all the functions you're excluding here have that bit set.

@efriedma-quic Great suggestion! Updated to check hasCustomTypechecking() instead of listing individual builtins. This is more maintainable and handles all builtins that use variadic declarations as an implementation detail.

github-actions · 2026-01-30T05:09:22Z

✅ With the latest revision this PR passed the C/C++ code linter.

mugiwaraluffy56 · 2026-01-31T12:44:10Z

@efriedma-quic @localspook @zeyi2 @PiotrZSL @vbvictor can you review this

clang-tools-extra/clang-tidy/cppcoreguidelines/ProTypeVarargCheck.cpp

github-actions · 2026-01-31T13:36:54Z

✅ With the latest revision this PR passed the C/C++ code formatter.

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 llvm#178629

zeyi2

LGTM :)

llvmbot added clang-tools-extra clang-tidy labels Jan 29, 2026

zeyi2 requested changes Jan 29, 2026

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zeyi2 requested review from PiotrZSL, localspook and vbvictor January 29, 2026 13:57

mugiwaraluffy56 force-pushed the fix-clang-tidy-hicpp-vararg-builtin branch from 3455ca6 to 183e6c6 Compare January 29, 2026 14:01

mugiwaraluffy56 requested a review from zeyi2 January 29, 2026 14:01

zeyi2 approved these changes Jan 29, 2026

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localspook mentioned this pull request Jan 29, 2026

Fix hicpp vararg popcountg #178709

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mugiwaraluffy56 force-pushed the fix-clang-tidy-hicpp-vararg-builtin branch from 183e6c6 to 5ce1602 Compare January 30, 2026 05:04

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[clang-tidy] Allow type-generic builtins in pro-type-vararg check #178656

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[clang-tidy] Allow type-generic builtins in pro-type-vararg check #178656

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