[clang] [clang] Predefine `_CRT_USE_BUILTIN_OFFSETOF` in MS-compatible modes (PR #127568)
A. Jiang via cfe-commits
cfe-commits at lists.llvm.org
Fri Feb 21 01:00:51 PST 2025
https://github.com/frederick-vs-ja updated https://github.com/llvm/llvm-project/pull/127568
>From 2c9e6e45944891af54cba9648297a996bb4d8cca Mon Sep 17 00:00:00 2001
From: "A. Jiang" <de34 at live.cn>
Date: Tue, 18 Feb 2025 14:03:35 +0800
Subject: [PATCH 1/2] [clang] Predefine `_CRT_USE_BUILTIN_OFFSETOF` in
MS-compatible modes
This patch makes Clang predefine `_CRT_USE_BUILTIN_OFFSETOF` in
MS-compatible modes. The macro can make the offsetof provided by MS
UCRT's `<stddef.h>` to select the `__builtin_offsetof` version,
so with it Clang (Clang-cl) can directly consume UCRT's `offsetof`.
MSVC predefines the macro as `1` since at least VS 2017 19.14, but I
think it's also OK to define it in "older" compatible modes.
---
clang/lib/Basic/Targets/OSTargets.cpp | 2 ++
clang/test/Sema/offsetof-ucrt.c | 17 +++++++++++++++++
clang/test/SemaCXX/offsetof-ucrt.cpp | 17 +++++++++++++++++
3 files changed, 36 insertions(+)
create mode 100644 clang/test/Sema/offsetof-ucrt.c
create mode 100644 clang/test/SemaCXX/offsetof-ucrt.cpp
diff --git a/clang/lib/Basic/Targets/OSTargets.cpp b/clang/lib/Basic/Targets/OSTargets.cpp
index 8af6623e5cb15..2e57c286c9a16 100644
--- a/clang/lib/Basic/Targets/OSTargets.cpp
+++ b/clang/lib/Basic/Targets/OSTargets.cpp
@@ -220,6 +220,8 @@ static void addVisualCDefines(const LangOptions &Opts, MacroBuilder &Builder) {
Builder.defineMacro("_MSC_FULL_VER", Twine(Opts.MSCompatibilityVersion));
// FIXME We cannot encode the revision information into 32-bits
Builder.defineMacro("_MSC_BUILD", Twine(1));
+ // https://github.com/llvm/llvm-project/issues/59689
+ Builder.defineMacro("_CRT_USE_BUILTIN_OFFSETOF", Twine(1));
if (Opts.CPlusPlus11 && Opts.isCompatibleWithMSVC(LangOptions::MSVC2015))
Builder.defineMacro("_HAS_CHAR16_T_LANGUAGE_SUPPORT", Twine(1));
diff --git a/clang/test/Sema/offsetof-ucrt.c b/clang/test/Sema/offsetof-ucrt.c
new file mode 100644
index 0000000000000..60c9ae3b5650e
--- /dev/null
+++ b/clang/test/Sema/offsetof-ucrt.c
@@ -0,0 +1,17 @@
+// RUN: %clang_cc1 %s -triple i686-pc-win32 -fsyntax-only -verify -fms-compatibility
+// expected-no-diagnostics
+
+typedef __typeof__(sizeof(0)) size_t;
+
+#if defined _MSC_VER && !defined _CRT_USE_BUILTIN_OFFSETOF
+#ifdef __cplusplus
+#define offsetof(s,m) ((::size_t)&reinterpret_cast<char const volatile&>((((s*)0)->m)))
+#else
+#define offsetof(s,m) ((size_t)&(((s*)0)->m))
+#endif
+#else
+#define offsetof(s,m) __builtin_offsetof(s,m)
+#endif
+
+struct S { int a; };
+_Static_assert(offsetof(struct S, a) == 0, "");
diff --git a/clang/test/SemaCXX/offsetof-ucrt.cpp b/clang/test/SemaCXX/offsetof-ucrt.cpp
new file mode 100644
index 0000000000000..a679fa01133f4
--- /dev/null
+++ b/clang/test/SemaCXX/offsetof-ucrt.cpp
@@ -0,0 +1,17 @@
+// RUN: %clang_cc1 %s -triple i686-pc-win32 -fsyntax-only -verify -fms-compatibility
+// expected-no-diagnostics
+
+typedef __typeof__(sizeof(0)) size_t;
+
+#if defined _MSC_VER && !defined _CRT_USE_BUILTIN_OFFSETOF
+#ifdef __cplusplus
+#define offsetof(s,m) ((::size_t)&reinterpret_cast<char const volatile&>((((s*)0)->m)))
+#else
+#define offsetof(s,m) ((size_t)&(((s*)0)->m))
+#endif
+#else
+#define offsetof(s,m) __builtin_offsetof(s,m)
+#endif
+
+struct S { int a; };
+_Static_assert(offsetof(S, a) == 0, "");
>From 4dc9bed47d7b4802e91b1774d8371e169f3f942c Mon Sep 17 00:00:00 2001
From: "A. Jiang" <de34 at live.cn>
Date: Fri, 21 Feb 2025 17:00:37 +0800
Subject: [PATCH 2/2] Address @AaronBallman's review comments
---
clang/lib/Basic/Targets/OSTargets.cpp | 2 +-
clang/test/Sema/offsetof-ucrt.c | 11 +++++++++++
clang/test/SemaCXX/offsetof-ucrt.cpp | 11 +++++++++++
3 files changed, 23 insertions(+), 1 deletion(-)
diff --git a/clang/lib/Basic/Targets/OSTargets.cpp b/clang/lib/Basic/Targets/OSTargets.cpp
index 2e57c286c9a16..e744e84a5b079 100644
--- a/clang/lib/Basic/Targets/OSTargets.cpp
+++ b/clang/lib/Basic/Targets/OSTargets.cpp
@@ -220,7 +220,7 @@ static void addVisualCDefines(const LangOptions &Opts, MacroBuilder &Builder) {
Builder.defineMacro("_MSC_FULL_VER", Twine(Opts.MSCompatibilityVersion));
// FIXME We cannot encode the revision information into 32-bits
Builder.defineMacro("_MSC_BUILD", Twine(1));
- // https://github.com/llvm/llvm-project/issues/59689
+ // Exposed by MSVC, used in their stddef.h.
Builder.defineMacro("_CRT_USE_BUILTIN_OFFSETOF", Twine(1));
if (Opts.CPlusPlus11 && Opts.isCompatibleWithMSVC(LangOptions::MSVC2015))
diff --git a/clang/test/Sema/offsetof-ucrt.c b/clang/test/Sema/offsetof-ucrt.c
index 60c9ae3b5650e..05c3d87ce66ca 100644
--- a/clang/test/Sema/offsetof-ucrt.c
+++ b/clang/test/Sema/offsetof-ucrt.c
@@ -1,8 +1,19 @@
// RUN: %clang_cc1 %s -triple i686-pc-win32 -fsyntax-only -verify -fms-compatibility
+// RUN: %clang_cc1 %s -triple i686-pc-win32 -fsyntax-only -verify
// expected-no-diagnostics
typedef __typeof__(sizeof(0)) size_t;
+#ifdef _MSC_VER
+#ifndef _CRT_USE_BUILTIN_OFFSETOF
+#error _CRT_USE_BUILTIN_OFFSETOF should be predefined in MSVC-compatible modes.
+#endif
+#else
+#ifdef _CRT_USE_BUILTIN_OFFSETOF
+#error _CRT_USE_BUILTIN_OFFSETOF should not be predefined in non-MSVC-compatible modes.
+#endif
+#endif
+
#if defined _MSC_VER && !defined _CRT_USE_BUILTIN_OFFSETOF
#ifdef __cplusplus
#define offsetof(s,m) ((::size_t)&reinterpret_cast<char const volatile&>((((s*)0)->m)))
diff --git a/clang/test/SemaCXX/offsetof-ucrt.cpp b/clang/test/SemaCXX/offsetof-ucrt.cpp
index a679fa01133f4..95437554c4665 100644
--- a/clang/test/SemaCXX/offsetof-ucrt.cpp
+++ b/clang/test/SemaCXX/offsetof-ucrt.cpp
@@ -1,8 +1,19 @@
// RUN: %clang_cc1 %s -triple i686-pc-win32 -fsyntax-only -verify -fms-compatibility
+// RUN: %clang_cc1 %s -triple i686-pc-win32 -fsyntax-only -verify
// expected-no-diagnostics
typedef __typeof__(sizeof(0)) size_t;
+#ifdef _MSC_VER
+#ifndef _CRT_USE_BUILTIN_OFFSETOF
+#error _CRT_USE_BUILTIN_OFFSETOF should be predefined in MSVC-compatible modes.
+#endif
+#else
+#ifdef _CRT_USE_BUILTIN_OFFSETOF
+#error _CRT_USE_BUILTIN_OFFSETOF should not be predefined in non-MSVC-compatible modes.
+#endif
+#endif
+
#if defined _MSC_VER && !defined _CRT_USE_BUILTIN_OFFSETOF
#ifdef __cplusplus
#define offsetof(s,m) ((::size_t)&reinterpret_cast<char const volatile&>((((s*)0)->m)))
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