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[libc] Fix generated float128 header for aarch64 target. #78017

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Merged
lntue merged 9 commits into from
Feb 5, 2024
Merged

[libc] Fix generated float128 header for aarch64 target. #78017

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4690a6c
[libc] Fix generated float128 header for aarch64 target.
lntue Jan 13, 2024
7e476e0
Fix formatting.
lntue Jan 13, 2024
e30b666
Sync and consolidate float128 type logic in one place.
lntue Jan 23, 2024
1014ffb
Add missing dependency and fix __copied_hdr__ target issues.
lntue Jan 23, 2024
a7773b3
Add TODO to update float128 type detection macros.
lntue Jan 23, 2024
0c53bce
Simplify float128 type detection macros.
lntue Feb 2, 2024
503687a
Fix ifdef.
lntue Feb 2, 2024
76aedc8
Exclude clang from using C23 _Float128 type.
lntue Feb 2, 2024
b66c904
Update float128 detection macros.
lntue Feb 3, 2024
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3 changes: 1 addition & 2 deletions libc/config/linux/aarch64/entrypoints.txt
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Expand Up @@ -379,8 +379,7 @@ set(TARGET_LIBM_ENTRYPOINTS
if(LIBC_COMPILER_HAS_FLOAT128)
list(APPEND TARGET_LIBM_ENTRYPOINTS
# math.h C23 _Float128 entrypoints
# Temporarily disabled since float128 isn't working on the aarch64 buildbot
# libc.src.math.fabsf128
libc.src.math.fabsf128
)
endif()

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2 changes: 1 addition & 1 deletion libc/config/linux/api.td
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Expand Up @@ -55,7 +55,7 @@ def IntTypesAPI : PublicAPI<"inttypes.h"> {
}

def MathAPI : PublicAPI<"math.h"> {
let Types = ["double_t", "float_t"];
let Types = ["double_t", "float_t", "float128"];
}

def FenvAPI: PublicAPI<"fenv.h"> {
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1 change: 1 addition & 0 deletions libc/include/CMakeLists.txt
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Expand Up @@ -100,6 +100,7 @@ add_gen_header(
.llvm-libc-macros.math_macros
.llvm-libc-types.double_t
.llvm-libc-types.float_t
.llvm-libc-types.float128
)

# TODO: This should be conditional on POSIX networking being included.
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7 changes: 7 additions & 0 deletions libc/include/llvm-libc-types/CMakeLists.txt
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Expand Up @@ -98,3 +98,10 @@ add_header(ENTRY HDR ENTRY.h)
add_header(struct_hsearch_data HDR struct_hsearch_data.h)
add_header(struct_epoll_event HDR struct_epoll_event.h)
add_header(struct_epoll_data HDR struct_epoll_data.h)
add_header(
float128
HDR
float128.h
DEPENDS
libc.include.llvm-libc-macros.float_macros
)
31 changes: 31 additions & 0 deletions libc/include/llvm-libc-types/float128.h
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@@ -0,0 +1,31 @@
//===-- Definition of float128 type ---------------------------------------===//
//
// 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_LIBC_TYPES_FLOAT128_H__
#define __LLVM_LIBC_TYPES_FLOAT128_H__

#include <include/llvm-libc-macros/float-macros.h> // LDBL_MANT_DIG

// TODO: https://github.com/llvm/llvm-project/issues/80195
// Check _Float128 C23 type detection again when clang supports it.
#if defined(__STDC_IEC_60559_BFP__) && !defined(__clang__)
// Use _Float128 C23 type.
#define LIBC_COMPILER_HAS_C23_FLOAT128
typedef _Float128 float128;
#elif defined(__FLOAT128__)
// Use __float128 type.
// clang uses __FLOAT128__ macro to notify the availability of __float128 type:
// https://reviews.llvm.org/D15120
#define LIBC_COMPILER_HAS_FLOAT128_EXTENSION
typedef __float128 float128;
#elif (LDBL_MANT_DIG == 113)
// Use long double.
typedef long double float128;
#endif
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@nickdesaulniers nickdesaulniers Feb 2, 2024 •
edited
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Argh, sorry for causing confusion here, but I do think we'll benefit in the long run by documenting the state of the world.

So some issues we've found:

  • gcc did not support _Float128 in C mode until gcc-7, and C++ mode until gcc-13.
  • gcc defines __STDC_IEC_60559_BFP__ to 201404L so we cannot compare __STDC_IEC_60559_BFP__ to 202311L (at least doing so won't work for any compiler TODAY). Just having this one check would be ideal, but alas.
  • clang doesn't support _Float128.
  • glibc will define __STDC_IEC_60559_BFP__ to 201404L, so we can't use it to detect compiler support in overlay mode (or not without great pain).

So perhaps we can have:

// GCC did not support _Float128 in C mode until gcc-7, or C++ mode until g++-13.
#if defined(__GNUC__) && !defined(clang) && \
    (defined(__cpluscplus) && __GNUC__ >= 13) || \
    (!defined(__cplusplus) && __GNUC__ >= 7)
#define LIBC_COMPILER_HAS_C23_FLOAT128
#endif

// TODO: replace when clang has actual _Float128 support.
// https://github.com/llvm/llvm-project/issues/80195
#ifdef __clang__
#define LIBC_COMPILER_HAS_FLOAT128_EXTENSION
#endif

#ifdef LIBC_COMPILER_HAS_C23_FLOAT128
typedef _Float128 float128;
#elif defined(LIBC_COMPILER_HAS_FLOAT128_EXTENSION)
typedef __float128 float128;
#elif LDBL_MANT_DIG == 113
typedef long double float128;
#else
#error "no f128 support"
#endif

I was hopefully naive that we could just have:

#if __STDC_IEC_60559_BFP__ < 202311L
#error "no _Float128 support"
#endif

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@lntue lntue Feb 3, 2024 •
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Let me summarize the current support in the following table:

                    |     clang      |   gcc pre-13   |     gcc-13     |   g++ pre-13   |     g++-13     |
----------------------------------------------------------------------------------------------------------
                    | x86-64 | arm64 | x86-64 | arm64 | x86-64 | arm64 | x86-64 | arm64 | x86-64 | arm64 |
----------------------------------------------------------------------------------------------------------
_Float128           |        |       |    X   |   X   |    X   |   X   |        |       |    X   |   X   |
----------------------------------------------------------------------------------------------------------
__float128          |    X   |       |    X   |       |    X   |       |    X   |       |    X   |       |
----------------------------------------------------------------------------------------------------------
long double as f128 |        |   X   |        |   X   |        |   X   |        |   X   |        |   X   |

So far the cleanest check I found without relying on compiler versioning or target architecture is follow:

#if defined(__STDC_IEC_60559_BFP__) && !defined(__clang__) && !defined(__cplusplus)
#define LIBC_COMPILER_HAS_C23_FLOAT128
#elif defined(__FLOAT128__) || defined(__SIZEOF_FLOAT128__)
#define LIBC_COMPILER_HAS_FLOAT128_EXTENSION
#elif (LDBL_MANT_DIG == 113)
// Use long double.
#define LIBC_LONG_DOUBLE_IS_FLOAT128
#endif

#ifdef LIBC_COMPILER_HAS_C23_FLOAT128
typedef _Float128 float128;
#elif defined(LIBC_COMPILER_HAS_FLOAT128_EXTENSION)
typedef __float128 float128;
#elif defined(LIBC_LONG_DOUBLE_IS_FLOAT128)
typedef long double float128;
#endif

with comments / TODO to revisit the conditions in the future when clang has support for _Float128.
WDYT?

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@nickdesaulniers nickdesaulniers Feb 5, 2024

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SGTM; we'll hopefully be revisiting this block of preprocessor checks when compilers improve their support. Let's get the build back to green.


#endif // __LLVM_LIBC_TYPES_FLOAT128_H__
2 changes: 1 addition & 1 deletion libc/spec/spec.td
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Expand Up @@ -53,7 +53,7 @@ def UnsignedCharType : NamedType<"unsigned char">;
def UnsignedShortType : NamedType<"unsigned short">;

// TODO: Add compatibility layer to use C23 type _Float128 if possible.
def Float128Type : NamedType<"__float128">;
def Float128Type : NamedType<"float128">;

// Common types
def VoidPtr : PtrType<VoidType>;
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1 change: 1 addition & 0 deletions libc/spec/stdc.td
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Expand Up @@ -352,6 +352,7 @@ def StdC : StandardSpec<"stdc"> {
[
NamedType<"float_t">,
NamedType<"double_t">,
NamedType<"float128">,
],
[], // Enumerations
[
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2 changes: 2 additions & 0 deletions libc/src/__support/macros/properties/CMakeLists.txt
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Expand Up @@ -33,4 +33,6 @@ add_header_library(
.compiler
.cpu_features
.os
libc.include.llvm-libc-macros.float_macros
libc.include.llvm-libc-types.float128
)
24 changes: 2 additions & 22 deletions libc/src/__support/macros/properties/float.h
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Expand Up @@ -11,13 +11,13 @@
#ifndef LLVM_LIBC_SRC___SUPPORT_MACROS_PROPERTIES_FLOAT_H
#define LLVM_LIBC_SRC___SUPPORT_MACROS_PROPERTIES_FLOAT_H

#include "include/llvm-libc-macros/float-macros.h" // LDBL_MANT_DIG
#include "include/llvm-libc-types/float128.h" // float128
#include "src/__support/macros/properties/architectures.h"
#include "src/__support/macros/properties/compiler.h"
#include "src/__support/macros/properties/cpu_features.h"
#include "src/__support/macros/properties/os.h"

#include <float.h> // LDBL_MANT_DIG

// 'long double' properties.
#if (LDBL_MANT_DIG == 53)
#define LIBC_LONG_DOUBLE_IS_FLOAT64
Expand Down Expand Up @@ -53,26 +53,6 @@ using float16 = _Float16;
#endif

// float128 support.
#if (defined(LIBC_COMPILER_GCC_VER) && (LIBC_COMPILER_GCC_VER >= 1301)) && \
(defined(LIBC_TARGET_ARCH_IS_AARCH64) || \
defined(LIBC_TARGET_ARCH_IS_ANY_RISCV) || \
defined(LIBC_TARGET_ARCH_IS_X86_64))
#define LIBC_COMPILER_HAS_C23_FLOAT128
#endif
#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

#if defined(LIBC_COMPILER_HAS_C23_FLOAT128)
using float128 = _Float128;
#elif defined(LIBC_COMPILER_HAS_FLOAT128_EXTENSION)
using float128 = __float128;
#elif defined(LIBC_LONG_DOUBLE_IS_FLOAT128)
using float128 = long double;
#endif

#if defined(LIBC_COMPILER_HAS_C23_FLOAT128) || \
defined(LIBC_COMPILER_HAS_FLOAT128_EXTENSION) || \
defined(LIBC_LONG_DOUBLE_IS_FLOAT128)
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