Fix __float128 only available on Linux for x86_64

[silver-popov]

Hello

It seems that CLang does not support float-128 extension, at least for x86-64 architecture.
For any OS, not only for fuchsia. So, following code causes a compilation error and should be removed.

#if (defined(LIBC_COMPILER_CLANG_VER) && (LIBC_COMPILER_CLANG_VER >= 500)) &&
(defined(LIBC_TARGET_ARCH_IS_X86_64) &&
!defined(LIBC_TARGET_OS_IS_FUCHSIA))
#define LIBC_COMPILER_HAS_FLOAT128_EXTENSION
#endif

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[llvmbot]

@llvm/pr-subscribers-libc

Author: Igor Popov (silver-popov)

Changes

Hello

It seems that CLang does not support float-128 extension, at least for x86-64 architecture.
For any OS, not only for fuchsia. So, following code causes a compilation error and should be removed.

#if (defined(LIBC_COMPILER_CLANG_VER) && (LIBC_COMPILER_CLANG_VER >= 500)) &&
(defined(LIBC_TARGET_ARCH_IS_X86_64) &&
!defined(LIBC_TARGET_OS_IS_FUCHSIA))
#define LIBC_COMPILER_HAS_FLOAT128_EXTENSION
#endif

---

Full diff: https://github.com/llvm/llvm-project/pull/75909.diff

1 Files Affected:

• (modified) libc/src/__support/macros/properties/float.h (-5)

diff --git a/libc/src/__support/macros/properties/float.h b/libc/src/__support/macros/properties/float.h
index 756579024cad8b..1953a6b6ef6250 100644
--- a/libc/src/__support/macros/properties/float.h
+++ b/libc/src/__support/macros/properties/float.h
@@ -59,11 +59,6 @@ using float16 = _Float16;
      defined(LIBC_TARGET_ARCH_IS_X86_64))
 #define LIBC_COMPILER_HAS_C23_FLOAT128
 #endif
-#if (defined(LIBC_COMPILER_CLANG_VER) && (LIBC_COMPILER_CLANG_VER >= 500)) &&  \
-    (defined(LIBC_TARGET_ARCH_IS_X86_64) &&                                    \
-     !defined(LIBC_TARGET_OS_IS_FUCHSIA))
-#define LIBC_COMPILER_HAS_FLOAT128_EXTENSION
-#endif
 
 #if defined(LIBC_COMPILER_HAS_C23_FLOAT128)
 using float128 = _Float128;

[gchatelet]

It seems to me that it does support float128 for x86_64.
https://godbolt.org/z/hqcfnnxc8

Although there is indeed a mistake, the condition should be >= 600 and not >= 500.

[silver-popov]

Although there is indeed a mistake, the condition should be >= 600 and not >= 500.

CLang 17 gives the error message:
llvm-project/libc/src/__support/FPUtil/FloatProperties.h:197:41: error: __float128 is not supported on this target

[gchatelet]

Although there is indeed a mistake, the condition should be >= 600 and not >= 500.

CLang 17 gives the error message: llvm-project/libc/src/__support/FPUtil/FloatProperties.h:197:41: error: __float128 is not supported on this target

I don't see this happening : https://godbolt.org/z/vsTbT13P1

Do you have a reproducer? Are you specifying a particular -march or any specific compiler options through LIBC_COMPILE_OPTIONS_DEFAULT or LIBC_COMMON_TUNE_OPTIONS?

[silver-popov]

I'm specifying LIBC_TARGET_TRIPLE="x86_64-pc-none-eabi"

[silver-popov]

The environment is MSYS2, CLang64.
Maybe the cause is MSYS2?

[silver-popov]

And why float-128 extension was disabled for Fuchsia?

[gchatelet]

The issue seems to be coming from OS support
https://godbolt.org/z/Y94o7KEKx

It is supported for --target=x86_64-pc-linux-eabi but not for --target=x86_64-pc-none-eabi nor --target=x86_64-pc-win32-eabi. So the proper guard should be:

#if (defined(LIBC_COMPILER_CLANG_VER) && (LIBC_COMPILER_CLANG_VER >= 600)) &&  \
    (defined(LIBC_TARGET_ARCH_IS_X86_64) &&                                    \
     defined(LIBC_TARGET_OS_IS_LINUX) && !defined(LIBC_TARGET_OS_IS_FUCHSIA))
#define LIBC_COMPILER_HAS_FLOAT128_EXTENSION
#endif

[silver-popov]

Compiles successfull. Committed.