[Clang-Tidy] Add google-runtime-float Clang-Tidy check #156763

brenfwd · 2025-09-03T22:02:25Z

Add a new checker to clang-tidy for use of the long double type per Google style guide.

github-actions · 2025-09-03T22:02:42Z

Thank you for submitting a Pull Request (PR) to the LLVM Project!

This PR will be automatically labeled and the relevant teams will be notified.

If you wish to, you can add reviewers by using the "Reviewers" section on this page.

If this is not working for you, it is probably because you do not have write permissions for the repository. In which case you can instead tag reviewers by name in a comment by using @ followed by their GitHub username.

If you have received no comments on your PR for a week, you can request a review by "ping"ing the PR by adding a comment “Ping”. The common courtesy "ping" rate is once a week. Please remember that you are asking for valuable time from other developers.

If you have further questions, they may be answered by the LLVM GitHub User Guide.

You can also ask questions in a comment on this PR, on the LLVM Discord or on the forums.

llvmbot · 2025-09-03T22:03:06Z

@llvm/pr-subscribers-clang-tidy

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

Author: None (brenfwd)

Changes

Add a new checker to clang-tidy for use of the long double type per Google style guide.

Full diff: https://github.com/llvm/llvm-project/pull/156763.diff

8 Files Affected:

(modified) clang-tools-extra/clang-tidy/google/CMakeLists.txt (+1)
(added) clang-tools-extra/clang-tidy/google/FloatTypesCheck.cpp (+80)
(added) clang-tools-extra/clang-tidy/google/FloatTypesCheck.h (+44)
(modified) clang-tools-extra/clang-tidy/google/GoogleTidyModule.cpp (+3)
(modified) clang-tools-extra/docs/ReleaseNotes.rst (+6)
(added) clang-tools-extra/docs/clang-tidy/checks/google/runtime-float.rst (+11)
(modified) clang-tools-extra/docs/clang-tidy/checks/list.rst (+2-1)
(added) clang-tools-extra/test/clang-tidy/checkers/google/runtime-float.cpp (+39)

diff --git a/clang-tools-extra/clang-tidy/google/CMakeLists.txt b/clang-tools-extra/clang-tidy/google/CMakeLists.txt
index 2470c089ef7ca..1d4229ebb7b09 100644
--- a/clang-tools-extra/clang-tidy/google/CMakeLists.txt
+++ b/clang-tools-extra/clang-tidy/google/CMakeLists.txt
@@ -11,6 +11,7 @@ add_clang_library(clangTidyGoogleModule STATIC
   DefaultArgumentsCheck.cpp
   ExplicitConstructorCheck.cpp
   ExplicitMakePairCheck.cpp
+  FloatTypesCheck.cpp
   FunctionNamingCheck.cpp
   GlobalNamesInHeadersCheck.cpp
   GlobalVariableDeclarationCheck.cpp
diff --git a/clang-tools-extra/clang-tidy/google/FloatTypesCheck.cpp b/clang-tools-extra/clang-tidy/google/FloatTypesCheck.cpp
new file mode 100644
index 0000000000000..b8afe803230d3
--- /dev/null
+++ b/clang-tools-extra/clang-tidy/google/FloatTypesCheck.cpp
@@ -0,0 +1,80 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "FloatTypesCheck.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+#include "clang/Lex/Lexer.h"
+
+namespace clang {
+
+using namespace ast_matchers;
+
+namespace {
+
+AST_MATCHER(TypeLoc, isTypeLocValidAndNotInMacro) {
+  const SourceLocation Loc = Node.getBeginLoc();
+  return Loc.isValid() && !Loc.isMacroID();
+}
+
+AST_MATCHER(FloatingLiteral, isFLValidAndNotInMacro) {
+  const SourceLocation Loc = Node.getBeginLoc();
+  return Loc.isValid() && !Loc.isMacroID();
+}
+
+AST_MATCHER(TypeLoc, isLongDoubleType) {
+  TypeLoc TL = Node;
+  if (auto QualLoc = Node.getAs<QualifiedTypeLoc>())
+    TL = QualLoc.getUnqualifiedLoc();
+
+  const auto BuiltinLoc = TL.getAs<BuiltinTypeLoc>();
+  if (!BuiltinLoc)
+    return false;
+
+  return BuiltinLoc.getTypePtr()->getKind() == BuiltinType::LongDouble;
+}
+
+AST_MATCHER(FloatingLiteral, isLongDoubleLiteral) {
+  if (auto *BT = dyn_cast<BuiltinType>(Node.getType().getTypePtr()))
+    return BT->getKind() == BuiltinType::LongDouble;
+  return false;
+}
+
+} // namespace
+
+namespace tidy::google::runtime {
+
+void RuntimeFloatCheck::registerMatchers(MatchFinder *Finder) {
+  Finder->addMatcher(typeLoc(loc(realFloatingPointType()),
+                             isTypeLocValidAndNotInMacro(), isLongDoubleType())
+                         .bind("longDoubleTypeLoc"),
+                     this);
+  Finder->addMatcher(
+      floatLiteral(isFLValidAndNotInMacro(), isLongDoubleLiteral())
+          .bind("longDoubleFloatLiteral"),
+      this);
+  IdentTable = std::make_unique<IdentifierTable>(getLangOpts());
+}
+
+void RuntimeFloatCheck::check(const MatchFinder::MatchResult &Result) {
+  if (const auto *TL = Result.Nodes.getNodeAs<TypeLoc>("longDoubleTypeLoc")) {
+    diag(TL->getBeginLoc(),
+         "consider replacing %0 with a 64-bit or 128-bit float type")
+        << TL->getType();
+  }
+
+  if (const auto *FL =
+          Result.Nodes.getNodeAs<FloatingLiteral>("longDoubleFloatLiteral")) {
+    diag(FL->getBeginLoc(),
+         "%0 type from literal suffix 'L' should not be used")
+        << FL->getType();
+  }
+}
+
+} // namespace tidy::google::runtime
+
+} // namespace clang
diff --git a/clang-tools-extra/clang-tidy/google/FloatTypesCheck.h b/clang-tools-extra/clang-tidy/google/FloatTypesCheck.h
new file mode 100644
index 0000000000000..54327b6d7e53b
--- /dev/null
+++ b/clang-tools-extra/clang-tidy/google/FloatTypesCheck.h
@@ -0,0 +1,44 @@
+
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_GOOGLE_FLOATTYPESCHECK_H
+#define LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_GOOGLE_FLOATTYPESCHECK_H
+
+#include "../ClangTidyCheck.h"
+
+namespace clang {
+
+class IdentifierTable;
+
+namespace tidy::google::runtime {
+
+/// Finds usages of `long double` and suggests replacing them with other
+/// floating-point types.
+///
+/// For the user-facing documentation see:
+/// http://clang.llvm.org/extra/clang-tidy/checks/google/runtime-float.html
+class RuntimeFloatCheck : public ClangTidyCheck {
+public:
+  RuntimeFloatCheck(StringRef Name, ClangTidyContext *Context)
+      : ClangTidyCheck(Name, Context) {}
+  void registerMatchers(ast_matchers::MatchFinder *Finder) override;
+  void check(const ast_matchers::MatchFinder::MatchResult &Result) override;
+  bool isLanguageVersionSupported(const LangOptions &LangOpts) const override {
+    return LangOpts.CPlusPlus && !LangOpts.ObjC;
+  }
+
+private:
+  std::unique_ptr<IdentifierTable> IdentTable;
+};
+
+} // namespace tidy::google::runtime
+
+} // namespace clang
+
+#endif // LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_GOOGLE_FLOATTYPESCHECK_H
diff --git a/clang-tools-extra/clang-tidy/google/GoogleTidyModule.cpp b/clang-tools-extra/clang-tidy/google/GoogleTidyModule.cpp
index 5343e2b3a5975..eb5666be62bcf 100644
--- a/clang-tools-extra/clang-tidy/google/GoogleTidyModule.cpp
+++ b/clang-tools-extra/clang-tidy/google/GoogleTidyModule.cpp
@@ -19,6 +19,7 @@
 #include "DefaultArgumentsCheck.h"
 #include "ExplicitConstructorCheck.h"
 #include "ExplicitMakePairCheck.h"
+#include "FloatTypesCheck.h"
 #include "FunctionNamingCheck.h"
 #include "GlobalNamesInHeadersCheck.h"
 #include "GlobalVariableDeclarationCheck.h"
@@ -57,6 +58,8 @@ class GoogleModule : public ClangTidyModule {
         "google-objc-function-naming");
     CheckFactories.registerCheck<objc::GlobalVariableDeclarationCheck>(
         "google-objc-global-variable-declaration");
+    CheckFactories.registerCheck<runtime::RuntimeFloatCheck>(
+        "google-runtime-float");
     CheckFactories.registerCheck<runtime::IntegerTypesCheck>(
         "google-runtime-int");
     CheckFactories.registerCheck<runtime::OverloadedUnaryAndCheck>(
diff --git a/clang-tools-extra/docs/ReleaseNotes.rst b/clang-tools-extra/docs/ReleaseNotes.rst
index 32e4dfb8aa329..af62797e9ea91 100644
--- a/clang-tools-extra/docs/ReleaseNotes.rst
+++ b/clang-tools-extra/docs/ReleaseNotes.rst
@@ -142,6 +142,12 @@ New checks
   Finds calls to ``operator[]`` in STL containers and suggests replacing them
   with safe alternatives.
 
+- New :doc:`google-runtime-float
+  <clang-tidy/checks/google/runtime-float>` check.
+
+  Checks for and warns of uses of the ``long double`` type, which is
+  problematic since it produces non-portable code.
+
 - New :doc:`llvm-mlir-op-builder
   <clang-tidy/checks/llvm/use-new-mlir-op-builder>` check.
 
diff --git a/clang-tools-extra/docs/clang-tidy/checks/google/runtime-float.rst b/clang-tools-extra/docs/clang-tidy/checks/google/runtime-float.rst
new file mode 100644
index 0000000000000..5a5f9a4e6ae0f
--- /dev/null
+++ b/clang-tools-extra/docs/clang-tidy/checks/google/runtime-float.rst
@@ -0,0 +1,11 @@
+.. title:: clang-tidy - google-runtime-float
+
+google-runtime-float
+====================
+
+Finds uses of ``long double`` and suggests replacing them with 64-bit
+or 128-bit floating-point types.
+
+The corresponding style guide rule:
+https://google.github.io/styleguide/cppguide.html#Floating-Point_Types
+
diff --git a/clang-tools-extra/docs/clang-tidy/checks/list.rst b/clang-tools-extra/docs/clang-tidy/checks/list.rst
index 5e3ffc4f8aca3..9c60c0766dbc4 100644
--- a/clang-tools-extra/docs/clang-tidy/checks/list.rst
+++ b/clang-tools-extra/docs/clang-tidy/checks/list.rst
@@ -238,6 +238,7 @@ Clang-Tidy Checks
    :doc:`google-readability-avoid-underscore-in-googletest-name <google/readability-avoid-underscore-in-googletest-name>`,
    :doc:`google-readability-casting <google/readability-casting>`,
    :doc:`google-readability-todo <google/readability-todo>`,
+   :doc:`google-runtime-float <google/runtime-float>`, "Yes"
    :doc:`google-runtime-int <google/runtime-int>`,
    :doc:`google-runtime-operator <google/runtime-operator>`,
    :doc:`google-upgrade-googletest-case <google/upgrade-googletest-case>`, "Yes"
@@ -249,12 +250,12 @@ Clang-Tidy Checks
    :doc:`linuxkernel-must-check-errs <linuxkernel/must-check-errs>`,
    :doc:`llvm-header-guard <llvm/header-guard>`,
    :doc:`llvm-include-order <llvm/include-order>`, "Yes"
-   :doc:`llvm-use-new-mlir-op-builder <llvm/use-new-mlir-op-builder>`, "Yes"
    :doc:`llvm-namespace-comment <llvm/namespace-comment>`,
    :doc:`llvm-prefer-isa-or-dyn-cast-in-conditionals <llvm/prefer-isa-or-dyn-cast-in-conditionals>`, "Yes"
    :doc:`llvm-prefer-register-over-unsigned <llvm/prefer-register-over-unsigned>`, "Yes"
    :doc:`llvm-prefer-static-over-anonymous-namespace <llvm/prefer-static-over-anonymous-namespace>`,
    :doc:`llvm-twine-local <llvm/twine-local>`, "Yes"
+   :doc:`llvm-use-new-mlir-op-builder <llvm/use-new-mlir-op-builder>`, "Yes"
    :doc:`llvmlibc-callee-namespace <llvmlibc/callee-namespace>`,
    :doc:`llvmlibc-implementation-in-namespace <llvmlibc/implementation-in-namespace>`,
    :doc:`llvmlibc-inline-function-decl <llvmlibc/inline-function-decl>`, "Yes"
diff --git a/clang-tools-extra/test/clang-tidy/checkers/google/runtime-float.cpp b/clang-tools-extra/test/clang-tidy/checkers/google/runtime-float.cpp
new file mode 100644
index 0000000000000..4ddf623fb955a
--- /dev/null
+++ b/clang-tools-extra/test/clang-tidy/checkers/google/runtime-float.cpp
@@ -0,0 +1,39 @@
+// RUN: %check_clang_tidy %s google-runtime-float %t
+
+long double foo;
+// CHECK-MESSAGES: :[[@LINE-1]]:1: warning: consider replacing 'long double' with a 64-bit or 128-bit float type [google-runtime-float]
+
+typedef long double MyLongDouble;
+// CHECK-MESSAGES: :[[@LINE-1]]:9: warning: consider replacing 'long double' with a 64-bit or 128-bit float type [google-runtime-float]
+
+typedef long double MyOtherLongDouble; // NOLINT
+
+template <typename T>
+void tmpl() { T i; }
+
+long volatile double v = 10;
+// CHECK-MESSAGES: :[[@LINE-1]]:1: warning: consider replacing 'volatile long double' with a 64-bit or 128-bit float type [google-runtime-float]
+
+long double h(long const double aaa, long double bbb = 0.5L) {
+  // CHECK-MESSAGES: :[[@LINE-1]]:1: warning: consider replacing 'long double' with a 64-bit or 128-bit float type [google-runtime-float]
+  // CHECK-MESSAGES: :[[@LINE-2]]:15: warning: consider replacing 'const long double' with a 64-bit or 128-bit float type [google-runtime-float]
+  // CHECK-MESSAGES: :[[@LINE-3]]:38: warning: consider replacing 'long double' with a 64-bit or 128-bit float type [google-runtime-float]
+  // CHECK-MESSAGES: :[[@LINE-4]]:56: warning: 'long double' type from literal suffix 'L' should not be used [google-runtime-float]
+  double x = 0.1;
+  double y = 0.2L;
+  // CHECK-MESSAGES: :[[@LINE-1]]:14: warning: 'long double' type from literal suffix 'L' should not be used [google-runtime-float]
+#define ldtype long double
+  ldtype z;
+  tmpl<long double>();
+  // CHECK-MESSAGES: :[[@LINE-1]]:8: warning: consider replacing 'long double' with a 64-bit or 128-bit float type [google-runtime-float]
+  return 0;
+}
+
+struct S{};
+constexpr S operator"" _baz(unsigned long long) {
+  long double j;
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: consider replacing 'long double' with a 64-bit or 128-bit float type [google-runtime-float]
+  MyOtherLongDouble x;
+  return S{};
+}
+

clang-tools-extra/docs/clang-tidy/checks/google/runtime-float.rst

clang-tools-extra/test/clang-tidy/checkers/google/runtime-float.cpp

clang-tools-extra/clang-tidy/google/FloatTypesCheck.cpp

nicovank · 2025-09-04T03:15:14Z

I think this can go straight into portability. Also linking this recent related PR: #146970.

clang-tools-extra/docs/clang-tidy/checks/google/runtime-float.rst

clang-tools-extra/test/clang-tidy/checkers/google/runtime-float.cpp

clang-tools-extra/docs/clang-tidy/checks/list.rst

clang-tools-extra/docs/clang-tidy/checks/google/runtime-float.rst

clang-tools-extra/docs/ReleaseNotes.rst

clang-tools-extra/clang-tidy/google/CMakeLists.txt

clang-tools-extra/clang-tidy/google/FloatTypesCheck.cpp

clang-tools-extra/clang-tidy/google/FloatTypesCheck.h

clang-tools-extra/test/clang-tidy/checkers/google/runtime-float.cpp

clang-tools-extra/docs/clang-tidy/checks/google/runtime-float.rst

carlosgalvezp · 2025-09-09T17:56:16Z

I think this can go straight into portability. Also linking this recent related PR: #146970.

It could go there and then have an alias to google if wanted maybe?

vbvictor · 2025-09-09T18:13:55Z

I think this can go straight into portability. Also linking this recent related PR: #146970.

It could go there and then have an alias to google if wanted maybe?

I'm weak +1 on this, portability-avoid-long-double maybe?
But if anything happens, we could add alias later.

nicovank · 2025-09-09T18:22:50Z

Looking at it again, this is fine for parity with google-runtime-int. No preference.

vbvictor

LGTM, minus open question with portability, but it doesn't block for me

github-actions · 2025-09-09T20:55:25Z

@brenfwd Congratulations on having your first Pull Request (PR) merged into the LLVM Project!

Your changes will be combined with recent changes from other authors, then tested by our build bots. If there is a problem with a build, you may receive a report in an email or a comment on this PR.

Please check whether problems have been caused by your change specifically, as the builds can include changes from many authors. It is not uncommon for your change to be included in a build that fails due to someone else's changes, or infrastructure issues.

How to do this, and the rest of the post-merge process, is covered in detail here.

If your change does cause a problem, it may be reverted, or you can revert it yourself. This is a normal part of LLVM development. You can fix your changes and open a new PR to merge them again.

If you don't get any reports, no action is required from you. Your changes are working as expected, well done!

brenfwd and others added 2 commits September 3, 2025 15:01

Add google-runtime-float Clang-Tidy check

1082254

Merge branch 'main' into add-clang-tidy-long-double

5ae76a0

llvmbot added clang-tools-extra clang-tidy labels Sep 3, 2025

alanzhao1 self-requested a review September 3, 2025 22:05

alanzhao1 approved these changes Sep 3, 2025

View reviewed changes

localspook requested review from PiotrZSL, carlosgalvezp, EugeneZelenko, vbvictor, HerrCai0907 and 5chmidti September 3, 2025 22:40

EugeneZelenko reviewed Sep 3, 2025

View reviewed changes

clang-tools-extra/docs/clang-tidy/checks/google/runtime-float.rst Outdated Show resolved Hide resolved

clang-tools-extra/test/clang-tidy/checkers/google/runtime-float.cpp Show resolved Hide resolved

Fix whitespace

8ef1f30

brenfwd requested a review from EugeneZelenko September 3, 2025 23:25

EugeneZelenko reviewed Sep 3, 2025

View reviewed changes

clang-tools-extra/clang-tidy/google/FloatTypesCheck.cpp Outdated Show resolved Hide resolved

clang-tools-extra/clang-tidy/google/FloatTypesCheck.cpp Outdated Show resolved Hide resolved

const-qualify values and remove unused member

26369d1

brenfwd requested a review from EugeneZelenko September 3, 2025 23:54

carlosgalvezp reviewed Sep 4, 2025

View reviewed changes

clang-tools-extra/docs/clang-tidy/checks/google/runtime-float.rst Outdated Show resolved Hide resolved

carlosgalvezp reviewed Sep 4, 2025

View reviewed changes

clang-tools-extra/test/clang-tidy/checkers/google/runtime-float.cpp Outdated Show resolved Hide resolved

HerrCai0907 reviewed Sep 4, 2025

View reviewed changes

clang-tools-extra/docs/clang-tidy/checks/list.rst Outdated Show resolved Hide resolved

Change diagnostics and docs entries

99acf39

brenfwd force-pushed the add-clang-tidy-long-double branch from 536f1a6 to 99acf39 Compare September 5, 2025 17:33

brenfwd requested review from HerrCai0907 and carlosgalvezp September 5, 2025 17:36

Fix class description comment

746d847

EugeneZelenko reviewed Sep 5, 2025

View reviewed changes

clang-tools-extra/docs/clang-tidy/checks/google/runtime-float.rst Outdated Show resolved Hide resolved

clang-tools-extra/docs/ReleaseNotes.rst Outdated Show resolved Hide resolved

Synchronize descriptions

7ff71dd

vbvictor reviewed Sep 5, 2025

View reviewed changes

Use variadic matcher and improve null-checking

aa45471

vbvictor reviewed Sep 6, 2025

View reviewed changes

clang-tools-extra/test/clang-tidy/checkers/google/runtime-float.cpp Show resolved Hide resolved

brenfwd and others added 2 commits September 9, 2025 10:08

Add long int test

bde6086

Merge branch 'main' into add-clang-tidy-long-double

c10d242

EugeneZelenko reviewed Sep 9, 2025

View reviewed changes

clang-tools-extra/docs/clang-tidy/checks/google/runtime-float.rst Outdated Show resolved Hide resolved

vbvictor approved these changes Sep 9, 2025

View reviewed changes

Fix word wrapping in doc

c225d7c

alanzhao1 merged commit ed9dded into llvm:main Sep 9, 2025
10 checks passed

brenfwd deleted the add-clang-tidy-long-double branch September 9, 2025 21:52

[Clang-Tidy] Add google-runtime-float Clang-Tidy check #156763

[Clang-Tidy] Add google-runtime-float Clang-Tidy check #156763

Conversation

brenfwd commented Sep 3, 2025

Uh oh!

github-actions bot commented Sep 3, 2025

Uh oh!

llvmbot commented Sep 3, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

nicovank commented Sep 4, 2025

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

carlosgalvezp commented Sep 9, 2025

Uh oh!

vbvictor commented Sep 9, 2025

Uh oh!

nicovank commented Sep 9, 2025

Uh oh!

vbvictor left a comment • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Uh oh!

github-actions bot commented Sep 9, 2025

Uh oh!

Uh oh!

llvmbot commented Sep 3, 2025 •

edited

Loading

vbvictor left a comment •

edited

Loading