[PATCH] Introduce __BIGGEST_ALIGNMENT__ macro
mats petersson
mats at planetcatfish.com
Mon Dec 15 00:48:01 PST 2014
On 15 December 2014 at 06:58, David Majnemer <david.majnemer at gmail.com> wrote:
> max_align_t is pretty useless, it doesn't account for fancy extended types
> at all. I assume __BIGGEST_ALIGNMENT__ does.
Not convinced that is the case (it would depend on the actual
definition of max_align_t and the value of SuitableAlignment - I'd
expect SuitableAlignment is the same as alignof(max_align_t) in, if
not all, at least the vast majority of cases). Both come out with the
same value in my quick test for x86. Not sure if there's a difference
on other platforms. Is there any evidence that this is the case, or is
this just speculation?
--
Mats
>
>
> On Sun, Dec 14, 2014 at 10:41 PM, Reid Kleckner <rnk at google.com> wrote:
>>
>> Is there a compelling reason to use __BIGGEST_ALIGNMENT__ over
>> max_align_t?
>>
>> On Sat, Dec 13, 2014 at 9:51 AM, mats petersson <mats at planetcatfish.com>
>> wrote:
>>>
>>> This is my first attempt for a patch to Clang, so please accept my
>>> apologies for any misconduct with regards to formatting, styling,
>>> content, culture, etc - and I hope that gmail doesn't munge the
>>> patch...
>>>
>>> The idea for this came about when at work (ARM) we discussed some code
>>> that had accidentally aligned it's sub-allocated block to 4 bytes for
>>> a 64-bit type, and got a unaligned access trap. So "how do you know",
>>> and someone found __BIGGEST_ALIGNMENT__ in gcc - but not available for
>>> Clang. So I thought I could add it, to make it a little more
>>> consistent between compilers...
>>>
>>> --
>>> Mats
>>>
>>> Add a predefined macro reflecting the largest alignment required by
>>> the archiecture, in bytes. This is useful for allocator designs that
>>> need to know the system alignment requirements. It reflects the
>>> TargetInfo.SuitableAlignment, converted to bytes (using CharWidth).
>>> ---
>>> lib/Frontend/InitPreprocessor.cpp | 4 ++++
>>> test/Preprocessor/init.c | 33
>>> +++++++++++++++++++++++++++++++++
>>> 2 files changed, 37 insertions(+), 0 deletions(-)
>>>
>>> diff --git a/lib/Frontend/InitPreprocessor.cpp
>>> b/lib/Frontend/InitPreprocessor.cpp
>>> index f4241a9..896277a 100644
>>> --- a/lib/Frontend/InitPreprocessor.cpp
>>> +++ b/lib/Frontend/InitPreprocessor.cpp
>>> @@ -710,6 +710,10 @@ static void InitializePredefinedMacros(const
>>> TargetInfo &TI,
>>> Builder.defineMacro("__POINTER_WIDTH__",
>>> Twine((int)TI.getPointerWidth(0)));
>>>
>>> + // Define __BIGGEST_ALIGNMENT__ to be compatible with gcc.
>>> + Builder.defineMacro("__BIGGEST_ALIGNMENT__",
>>> + Twine(TI.getSuitableAlign() / TI.getCharWidth())
>>> );
>>> +
>>> if (!LangOpts.CharIsSigned)
>>> Builder.defineMacro("__CHAR_UNSIGNED__");
>>>
>>> diff --git a/test/Preprocessor/init.c b/test/Preprocessor/init.c
>>> index 4f32114..924aa5b 100644
>>> --- a/test/Preprocessor/init.c
>>> +++ b/test/Preprocessor/init.c
>>> @@ -241,6 +241,7 @@
>>> // AARCH64:#define __ARM_ARCH 8
>>> // AARCH64:#define __ARM_ARCH_ISA_A64 1
>>> // AARCH64-NOT:#define __ARM_BIG_ENDIAN 1
>>> +// AARCH64:#define __BIGGEST_ALIGNMENT__ 8
>>> // AARCH64:#define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__
>>> // AARCH64:#define __CHAR16_TYPE__ unsigned short
>>> // AARCH64:#define __CHAR32_TYPE__ unsigned int
>>> @@ -431,6 +432,7 @@
>>> // AARCH64-BE:#define __ARM_ARCH 8
>>> // AARCH64-BE:#define __ARM_ARCH_ISA_A64 1
>>> // AARCH64-BE:#define __ARM_BIG_ENDIAN 1
>>> +// AARCH64-BE:#define __BIGGEST_ALIGNMENT__ 8
>>> // AARCH64-BE:#define __BYTE_ORDER__ __ORDER_BIG_ENDIAN__
>>> // AARCH64-BE:#define __CHAR16_TYPE__ unsigned short
>>> // AARCH64-BE:#define __CHAR32_TYPE__ unsigned int
>>> @@ -621,6 +623,7 @@
>>> // AARCH64-NETBSD:#define __ARM_ARCH 8
>>> // AARCH64-NETBSD:#define __ARM_ARCH_ISA_A64 1
>>> // AARCH64-NETBSD-NOT:#define __ARM_BIG_ENDIAN 1
>>> +// AARCH64-NETBSD:#define __BIGGEST_ALIGNMENT__ 8
>>> // AARCH64-NETBSD:#define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__
>>> // AARCH64-NETBSD:#define __CHAR16_TYPE__ unsigned short
>>> // AARCH64-NETBSD:#define __CHAR32_TYPE__ unsigned int
>>> @@ -812,6 +815,7 @@
>>> // AARCH64-FREEBSD:#define __ARM_ARCH 8
>>> // AARCH64-FREEBSD:#define __ARM_ARCH_ISA_A64 1
>>> // AARCH64-FREEBSD-NOT:#define __ARM_BIG_ENDIAN 1
>>> +// AARCH64-FREEBSD:#define __BIGGEST_ALIGNMENT__ 8
>>> // AARCH64-FREEBSD:#define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__
>>> // AARCH64-FREEBSD:#define __CHAR16_TYPE__ unsigned short
>>> // AARCH64-FREEBSD:#define __CHAR32_TYPE__ unsigned int
>>> @@ -1003,6 +1007,7 @@
>>> // ARM:#define __ARMEL__ 1
>>> // ARM:#define __ARM_ARCH_6J__ 1
>>> // ARM-NOT:#define __ARM_BIG_ENDIAN 1
>>> +// ARM:#define __BIGGEST_ALIGNMENT__ 8
>>> // ARM:#define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__
>>> // ARM:#define __CHAR16_TYPE__ unsigned short
>>> // ARM:#define __CHAR32_TYPE__ unsigned int
>>> @@ -1193,6 +1198,7 @@
>>> // ARM-BE-NOT:#define __ARMEL__ 1
>>> // ARM-BE:#define __ARM_ARCH_6J__ 1
>>> // ARM-BE:#define __ARM_BIG_ENDIAN 1
>>> +// ARM-BE:#define __BIGGEST_ALIGNMENT__ 8
>>> // ARM-BE:#define __BIG_ENDIAN__ 1
>>> // ARM-BE:#define __BYTE_ORDER__ __ORDER_BIG_ENDIAN__
>>> // ARM-BE:#define __CHAR16_TYPE__ unsigned short
>>> @@ -1387,6 +1393,7 @@
>>> // ARMEABISOFTFP:#define __ARM_EABI__ 1
>>> // ARMEABISOFTFP:#define __ARM_PCS 1
>>> // ARMEABISOFTFP-NOT:#define __ARM_PCS_VFP 1
>>> +// ARMEABISOFTFP:#define __BIGGEST_ALIGNMENT__ 8
>>> // ARMEABISOFTFP:#define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__
>>> // ARMEABISOFTFP:#define __CHAR16_TYPE__ unsigned short
>>> // ARMEABISOFTFP:#define __CHAR32_TYPE__ unsigned int
>>> @@ -1582,6 +1589,7 @@
>>> // ARMEABIHARDFP:#define __ARM_EABI__ 1
>>> // ARMEABIHARDFP:#define __ARM_PCS 1
>>> // ARMEABIHARDFP:#define __ARM_PCS_VFP 1
>>> +// ARMEABIHARDFP:#define __BIGGEST_ALIGNMENT__ 8
>>> // ARMEABIHARDFP:#define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__
>>> // ARMEABIHARDFP:#define __CHAR16_TYPE__ unsigned short
>>> // ARMEABIHARDFP:#define __CHAR32_TYPE__ unsigned int
>>> @@ -1775,6 +1783,7 @@
>>> // ARM-NETBSD:#define __ARM_DWARF_EH__ 1
>>> // ARM-NETBSD:#define __ARM_EABI__ 1
>>> // ARM-NETBSD-NOT:#define __ARM_BIG_ENDIAN 1
>>> +// ARM-NETBSD:#define __BIGGEST_ALIGNMENT__ 8
>>> // ARM-NETBSD:#define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__
>>> // ARM-NETBSD:#define __CHAR16_TYPE__ unsigned short
>>> // ARM-NETBSD:#define __CHAR32_TYPE__ unsigned int
>>> @@ -2021,6 +2030,7 @@
>>> // RUN: %clang_cc1 -E -dM -ffreestanding -triple=i386-none-none <
>>> /dev/null | FileCheck -check-prefix I386 %s
>>> //
>>> // I386-NOT:#define _LP64
>>> +// I386:#define __BIGGEST_ALIGNMENT__ 16
>>> // I386:#define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__
>>> // I386:#define __CHAR16_TYPE__ unsigned short
>>> // I386:#define __CHAR32_TYPE__ unsigned int
>>> @@ -2207,6 +2217,7 @@
>>> // RUN: %clang_cc1 -E -dM -ffreestanding -triple=i386-pc-linux-gnu
>>> -target-cpu pentium4 < /dev/null | FileCheck -check-prefix I386-LINUX
>>> %s
>>> //
>>> // I386-LINUX-NOT:#define _LP64
>>> +// I386-LINUX:#define __BIGGEST_ALIGNMENT__ 16
>>> // I386-LINUX:#define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__
>>> // I386-LINUX:#define __CHAR16_TYPE__ unsigned short
>>> // I386-LINUX:#define __CHAR32_TYPE__ unsigned int
>>> @@ -2393,6 +2404,7 @@
>>> // RUN: %clang_cc1 -E -dM -ffreestanding -triple=i386-netbsd <
>>> /dev/null | FileCheck -check-prefix I386-NETBSD %s
>>> //
>>> // I386-NETBSD-NOT:#define _LP64
>>> +// I386-NETBSD:#define __BIGGEST_ALIGNMENT__ 16
>>> // I386-NETBSD:#define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__
>>> // I386-NETBSD:#define __CHAR16_TYPE__ unsigned short
>>> // I386-NETBSD:#define __CHAR32_TYPE__ unsigned int
>>> @@ -2597,6 +2609,7 @@
>>> // MIPS32BE:#define _MIPS_SZINT 32
>>> // MIPS32BE:#define _MIPS_SZLONG 32
>>> // MIPS32BE:#define _MIPS_SZPTR 32
>>> +// MIPS32BE:#define __BIGGEST_ALIGNMENT__ 8
>>> // MIPS32BE:#define __BIG_ENDIAN__ 1
>>> // MIPS32BE:#define __BYTE_ORDER__ __ORDER_BIG_ENDIAN__
>>> // MIPS32BE:#define __CHAR16_TYPE__ unsigned short
>>> @@ -2805,6 +2818,7 @@
>>> // MIPS32EL:#define _MIPS_SZINT 32
>>> // MIPS32EL:#define _MIPS_SZLONG 32
>>> // MIPS32EL:#define _MIPS_SZPTR 32
>>> +// MIPS32EL:#define __BIGGEST_ALIGNMENT__ 8
>>> // MIPS32EL:#define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__
>>> // MIPS32EL:#define __CHAR16_TYPE__ unsigned short
>>> // MIPS32EL:#define __CHAR32_TYPE__ unsigned int
>>> @@ -3010,6 +3024,7 @@
>>> // MIPS64BE:#define _MIPS_SZINT 32
>>> // MIPS64BE:#define _MIPS_SZLONG 64
>>> // MIPS64BE:#define _MIPS_SZPTR 64
>>> +// MIPS64BE:#define __BIGGEST_ALIGNMENT__ 16
>>> // MIPS64BE:#define __BIG_ENDIAN__ 1
>>> // MIPS64BE:#define __BYTE_ORDER__ __ORDER_BIG_ENDIAN__
>>> // MIPS64BE:#define __CHAR16_TYPE__ unsigned short
>>> @@ -3218,6 +3233,7 @@
>>> // MIPS64EL:#define _MIPS_SZINT 32
>>> // MIPS64EL:#define _MIPS_SZLONG 64
>>> // MIPS64EL:#define _MIPS_SZPTR 64
>>> +// MIPS64EL:#define __BIGGEST_ALIGNMENT__ 16
>>> // MIPS64EL:#define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__
>>> // MIPS64EL:#define __CHAR16_TYPE__ unsigned short
>>> // MIPS64EL:#define __CHAR32_TYPE__ unsigned int
>>> @@ -3583,6 +3599,7 @@
>>> //
>>> // MSP430:#define MSP430 1
>>> // MSP430-NOT:#define _LP64
>>> +// MSP430:#define __BIGGEST_ALIGNMENT__ 2
>>> // MSP430:#define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__
>>> // MSP430:#define __CHAR16_TYPE__ unsigned short
>>> // MSP430:#define __CHAR32_TYPE__ unsigned int
>>> @@ -3766,6 +3783,7 @@
>>> // RUN: %clang_cc1 -E -dM -ffreestanding -triple=nvptx-none-none <
>>> /dev/null | FileCheck -check-prefix NVPTX32 %s
>>> //
>>> // NVPTX32-NOT:#define _LP64
>>> +// NVPTX32:#define __BIGGEST_ALIGNMENT__ 8
>>> // NVPTX32:#define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__
>>> // NVPTX32:#define __CHAR16_TYPE__ unsigned short
>>> // NVPTX32:#define __CHAR32_TYPE__ unsigned int
>>> @@ -3952,6 +3970,7 @@
>>> // RUN: %clang_cc1 -E -dM -ffreestanding -triple=nvptx64-none-none <
>>> /dev/null | FileCheck -check-prefix NVPTX64 %s
>>> //
>>> // NVPTX64:#define _LP64 1
>>> +// NVPTX64:#define __BIGGEST_ALIGNMENT__ 8
>>> // NVPTX64:#define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__
>>> // NVPTX64:#define __CHAR16_TYPE__ unsigned short
>>> // NVPTX64:#define __CHAR32_TYPE__ unsigned int
>>> @@ -4143,6 +4162,7 @@
>>> // PPC603E:#define _ARCH_PPCGR 1
>>> // PPC603E:#define _BIG_ENDIAN 1
>>> // PPC603E-NOT:#define _LP64
>>> +// PPC603E:#define __BIGGEST_ALIGNMENT__ 8
>>> // PPC603E:#define __BIG_ENDIAN__ 1
>>> // PPC603E:#define __BYTE_ORDER__ __ORDER_BIG_ENDIAN__
>>> // PPC603E:#define __CHAR16_TYPE__ unsigned short
>>> @@ -4340,6 +4360,7 @@
>>> // PPC64:#define _ARCH_PWR7 1
>>> // PPC64:#define _BIG_ENDIAN 1
>>> // PPC64:#define _LP64 1
>>> +// PPC64:#define __BIGGEST_ALIGNMENT__ 8
>>> // PPC64:#define __BIG_ENDIAN__ 1
>>> // PPC64:#define __BYTE_ORDER__ __ORDER_BIG_ENDIAN__
>>> // PPC64:#define __CHAR16_TYPE__ unsigned short
>>> @@ -4542,6 +4563,7 @@
>>> // PPC64LE:#define _CALL_ELF 2
>>> // PPC64LE:#define _LITTLE_ENDIAN 1
>>> // PPC64LE:#define _LP64 1
>>> +// PPC64LE:#define __BIGGEST_ALIGNMENT__ 8
>>> // PPC64LE:#define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__
>>> // PPC64LE:#define __CHAR16_TYPE__ unsigned short
>>> // PPC64LE:#define __CHAR32_TYPE__ unsigned int
>>> @@ -4923,6 +4945,7 @@
>>> // PPC64-LINUX:#define _ARCH_PPC64 1
>>> // PPC64-LINUX:#define _BIG_ENDIAN 1
>>> // PPC64-LINUX:#define _LP64 1
>>> +// PPC64-LINUX:#define __BIGGEST_ALIGNMENT__ 8
>>> // PPC64-LINUX:#define __BIG_ENDIAN__ 1
>>> // PPC64-LINUX:#define __BYTE_ORDER__ __ORDER_BIG_ENDIAN__
>>> // PPC64-LINUX:#define __CHAR16_TYPE__ unsigned short
>>> @@ -5127,6 +5150,7 @@
>>> // PPC:#define _ARCH_PPC 1
>>> // PPC:#define _BIG_ENDIAN 1
>>> // PPC-NOT:#define _LP64
>>> +// PPC:#define __BIGGEST_ALIGNMENT__ 8
>>> // PPC:#define __BIG_ENDIAN__ 1
>>> // PPC:#define __BYTE_ORDER__ __ORDER_BIG_ENDIAN__
>>> // PPC:#define __CHAR16_TYPE__ unsigned short
>>> @@ -5317,6 +5341,7 @@
>>> // PPC-LINUX:#define _ARCH_PPC 1
>>> // PPC-LINUX:#define _BIG_ENDIAN 1
>>> // PPC-LINUX-NOT:#define _LP64
>>> +// PPC-LINUX:#define __BIGGEST_ALIGNMENT__ 8
>>> // PPC-LINUX:#define __BIG_ENDIAN__ 1
>>> // PPC-LINUX:#define __BYTE_ORDER__ __ORDER_BIG_ENDIAN__
>>> // PPC-LINUX:#define __CHAR16_TYPE__ unsigned short
>>> @@ -5508,6 +5533,7 @@
>>> //
>>> // PPC-DARWIN:#define _ARCH_PPC 1
>>> // PPC-DARWIN:#define _BIG_ENDIAN 1
>>> +// PPC-DARWIN:#define __BIGGEST_ALIGNMENT__ 16
>>> // PPC-DARWIN:#define __BIG_ENDIAN__ 1
>>> // PPC-DARWIN:#define __BYTE_ORDER__ __ORDER_BIG_ENDIAN__
>>> // PPC-DARWIN:#define __CHAR16_TYPE__ unsigned short
>>> @@ -5701,6 +5727,7 @@
>>> //
>>> // RUN: %clang_cc1 -E -dM -ffreestanding -triple=s390x-none-none
>>> -fno-signed-char < /dev/null | FileCheck -check-prefix S390X %s
>>> //
>>> +// S390X:#define __BIGGEST_ALIGNMENT__ 8
>>> // S390X:#define __CHAR16_TYPE__ unsigned short
>>> // S390X:#define __CHAR32_TYPE__ unsigned int
>>> // S390X:#define __CHAR_BIT__ 8
>>> @@ -5882,6 +5909,7 @@
>>> // RUN: %clang_cc1 -E -dM -ffreestanding -triple=sparc-none-none <
>>> /dev/null | FileCheck -check-prefix SPARC %s
>>> //
>>> // SPARC-NOT:#define _LP64
>>> +// SPARC:#define __BIGGEST_ALIGNMENT__ 8
>>> // SPARC:#define __BIG_ENDIAN__ 1
>>> // SPARC:#define __BYTE_ORDER__ __ORDER_BIG_ENDIAN__
>>> // SPARC:#define __CHAR16_TYPE__ unsigned short
>>> @@ -6069,6 +6097,7 @@
>>> // RUN: %clang_cc1 -E -dM -ffreestanding -triple=tce-none-none <
>>> /dev/null | FileCheck -check-prefix TCE %s
>>> //
>>> // TCE-NOT:#define _LP64
>>> +// TCE:#define __BIGGEST_ALIGNMENT__ 4
>>> // TCE:#define __BIG_ENDIAN__ 1
>>> // TCE:#define __BYTE_ORDER__ __ORDER_BIG_ENDIAN__
>>> // TCE:#define __CHAR16_TYPE__ unsigned short
>>> @@ -6236,6 +6265,7 @@
>>> //
>>> // X86_64:#define _LP64 1
>>> // X86_64-NOT:#define _LP32 1
>>> +// X86_64:#define __BIGGEST_ALIGNMENT__ 16
>>> // X86_64:#define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__
>>> // X86_64:#define __CHAR16_TYPE__ unsigned short
>>> // X86_64:#define __CHAR32_TYPE__ unsigned int
>>> @@ -6437,6 +6467,7 @@
>>> //
>>> // X32:#define _ILP32 1
>>> // X32-NOT:#define _LP64 1
>>> +// X32:#define __BIGGEST_ALIGNMENT__ 16
>>> // X32:#define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__
>>> // X32:#define __CHAR16_TYPE__ unsigned short
>>> // X32:#define __CHAR32_TYPE__ unsigned int
>>> @@ -6630,6 +6661,7 @@
>>> // RUN: %clang_cc1 -E -dM -ffreestanding -triple=x86_64-pc-linux-gnu
>>> < /dev/null | FileCheck -check-prefix X86_64-LINUX %s
>>> //
>>> // X86_64-LINUX:#define _LP64 1
>>> +// X86_64-LINUX:#define __BIGGEST_ALIGNMENT__ 16
>>> // X86_64-LINUX:#define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__
>>> // X86_64-LINUX:#define __CHAR16_TYPE__ unsigned short
>>> // X86_64-LINUX:#define __CHAR32_TYPE__ unsigned int
>>> @@ -6828,6 +6860,7 @@
>>> // RUN: %clang_cc1 -E -dM -ffreestanding -triple=x86_64-netbsd <
>>> /dev/null | FileCheck -check-prefix X86_64-NETBSD %s
>>> //
>>> // X86_64-NETBSD:#define _LP64 1
>>> +// X86_64-NETBSD:#define __BIGGEST_ALIGNMENT__ 16
>>> // X86_64-NETBSD:#define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__
>>> // X86_64-NETBSD:#define __CHAR16_TYPE__ unsigned short
>>> // X86_64-NETBSD:#define __CHAR32_TYPE__ unsigned int
>>> --
>>> 1.7.7.6
>>> _______________________________________________
>>> cfe-commits mailing list
>>> cfe-commits at cs.uiuc.edu
>>> http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits
>>
>>
>> _______________________________________________
>> cfe-commits mailing list
>> cfe-commits at cs.uiuc.edu
>> http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits
>>
>
More information about the cfe-commits
mailing list