[libc-commits] [libc] [libc] fix type generic stdc_leading_zeros for GCC (PR #79917)

[Nick Desaulniers via libc-commits]

https://github.com/nickdesaulniers created https://github.com/llvm/llvm-project/pull/79917

GCC does not support _Generic in C++ mode. Use inline function definitions
with function overloading in __cplusplus mode.


>From f1ab63dad859dc66e4fd32188b87a7974259d57e Mon Sep 17 00:00:00 2001
From: Nick Desaulniers <ndesaulniers at google.com>
Date: Mon, 29 Jan 2024 16:26:11 -0800
Subject: [PATCH] [libc] fix type generic stdc_leading_zeros for GCC

GCC does not support _Generic in C++ mode. Use inline function definitions
with function overloading in __cplusplus mode.
---
 libc/include/llvm-libc-macros/stdbit-macros.h | 18 ++++++++++++++++++
 libc/include/stdbit.h.def                     |  3 ++-
 2 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/libc/include/llvm-libc-macros/stdbit-macros.h b/libc/include/llvm-libc-macros/stdbit-macros.h
index febe95fe0a1e3..da0fb1a578f13 100644
--- a/libc/include/llvm-libc-macros/stdbit-macros.h
+++ b/libc/include/llvm-libc-macros/stdbit-macros.h
@@ -9,6 +9,23 @@
 #ifndef __LLVM_LIBC_MACROS_STDBIT_MACROS_H
 #define __LLVM_LIBC_MACROS_STDBIT_MACROS_H
 
+#ifdef __cplusplus
+inline unsigned char stdc_leading_zeros(unsigned char x) {
+  return stdc_leading_zeros_uc(x);
+}
+inline unsigned short stdc_leading_zeros(unsigned short x) {
+  return stdc_leading_zeros_us(x);
+}
+inline unsigned stdc_leading_zeros(unsigned x) {
+  return stdc_leading_zeros_ui(x);
+}
+inline unsigned long stdc_leading_zeros(unsigned long x) {
+  return stdc_leading_zeros_ul(x);
+}
+inline unsigned long long stdc_leading_zeros(unsigned long long x) {
+  return stdc_leading_zeros_ull(x);
+}
+#else
 #define stdc_leading_zeros(x)                                                  \
   _Generic((x),                                                                \
       unsigned char: stdc_leading_zeros_uc,                                    \
@@ -16,5 +33,6 @@
       unsigned: stdc_leading_zeros_ui,                                         \
       unsigned long: stdc_leading_zeros_ul,                                    \
       unsigned long long: stdc_leading_zeros_ull)(x)
+#endif // __cplusplus
 
 #endif // __LLVM_LIBC_MACROS_STDBIT_MACROS_H
diff --git a/libc/include/stdbit.h.def b/libc/include/stdbit.h.def
index cb79ac1caf049..c5a77329fbfe7 100644
--- a/libc/include/stdbit.h.def
+++ b/libc/include/stdbit.h.def
@@ -10,8 +10,9 @@
 #define LLVM_LIBC_STDBIT_H
 
 #include <__llvm-libc-common.h>
-#include <llvm-libc-macros/stdbit-macros.h>
 
 %%public_api()
 
+#include <llvm-libc-macros/stdbit-macros.h>
+
 #endif // LLVM_LIBC_STDBIT_H