On 15 December 2014 at 06:58, David Majnemer <[email protected]> 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 <[email protected]> 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 <[email protected]> >> 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 >>> [email protected] >>> http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits >> >> >> _______________________________________________ >> cfe-commits mailing list >> [email protected] >> http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits >> > _______________________________________________ cfe-commits mailing list [email protected] http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits
