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eeb828f029
In both Clang and LLVM, this is a common pattern: Size = sizeof(DeclRefExpr) + SomeExtraStuff; void *Mem = Context.Allocate(Size, llvm::alignOf<DeclRefExpr>()); return new (Mem) DeclRefExpr(...); The annoying thing is that because the default placement-new operator has a nothrow specification, the compiler will insert a null check of Mem before calling the DeclRefExpr constructor. This null check is redundant for us, because we expect the allocation functions to never return null. By annotating the allocator functions with returns_nonnull, we can optimize away these checks. Compiling clang with a recent version of Clang and measuring with: $ perf stat -r20 bin/clang.patch -fsyntax-only -w gcc.c && perf stat -r20 bin/clang.orig -fsyntax-only -w gcc.c Shows a 2.4% speed-up (+- 0.8%). The pattern occurs in LLVM too. Measuring with -O3 (and now using bzip2.c instead, because it's smaller): $ perf stat -r20 bin/clang.patch -O3 -w bzip2.c && perf stat -r20 bin/clang.orig -O3 -w bzip2.c Shows 4.4 % speed-up (+- 1%). If anyone knows of a similar attribute we can use for MSVC, or some other technique to get rid off the null check there, please let me know. Differential Revision: http://reviews.llvm.org/D4989 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@216192 91177308-0d34-0410-b5e6-96231b3b80d8
368 lines
12 KiB
C++
368 lines
12 KiB
C++
//===-- llvm/Support/Compiler.h - Compiler abstraction support --*- C++ -*-===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file defines several macros, based on the current compiler. This allows
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// use of compiler-specific features in a way that remains portable.
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_SUPPORT_COMPILER_H
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#define LLVM_SUPPORT_COMPILER_H
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#include "llvm/Config/llvm-config.h"
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#ifndef __has_feature
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# define __has_feature(x) 0
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#endif
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#ifndef __has_extension
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# define __has_extension(x) 0
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#endif
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#ifndef __has_attribute
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# define __has_attribute(x) 0
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#endif
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#ifndef __has_builtin
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# define __has_builtin(x) 0
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#endif
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/// \macro __GNUC_PREREQ
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/// \brief Defines __GNUC_PREREQ if glibc's features.h isn't available.
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#ifndef __GNUC_PREREQ
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# if defined(__GNUC__) && defined(__GNUC_MINOR__)
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# define __GNUC_PREREQ(maj, min) \
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((__GNUC__ << 16) + __GNUC_MINOR__ >= ((maj) << 16) + (min))
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# else
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# define __GNUC_PREREQ(maj, min) 0
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# endif
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#endif
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/// \macro LLVM_MSC_PREREQ
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/// \brief Is the compiler MSVC of at least the specified version?
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/// The common \param version values to check for are:
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/// * 1700: Microsoft Visual Studio 2012 / 11.0
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/// * 1800: Microsoft Visual Studio 2013 / 12.0
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#ifdef _MSC_VER
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#define LLVM_MSC_PREREQ(version) (_MSC_VER >= (version))
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// We require at least MSVC 2012.
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#if !LLVM_MSC_PREREQ(1700)
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#error LLVM requires at least MSVC 2012.
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#endif
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#else
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#define LLVM_MSC_PREREQ(version) 0
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#endif
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#ifndef _MSC_VER
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#define LLVM_NOEXCEPT noexcept
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#else
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#define LLVM_NOEXCEPT
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#endif
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/// \brief Does the compiler support r-value reference *this?
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///
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/// Sadly, this is separate from just r-value reference support because GCC
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/// implemented everything but this thus far. No release of GCC yet has support
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/// for this feature so it is enabled with Clang only.
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/// FIXME: This should change to a version check when GCC grows support for it.
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#if __has_feature(cxx_rvalue_references)
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#define LLVM_HAS_RVALUE_REFERENCE_THIS 1
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#else
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#define LLVM_HAS_RVALUE_REFERENCE_THIS 0
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#endif
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/// \macro LLVM_HAS_VARIADIC_TEMPLATES
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/// \brief Does this compiler support variadic templates.
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///
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/// Implies LLVM_HAS_RVALUE_REFERENCES and the existence of std::forward.
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#if __has_feature(cxx_variadic_templates) || LLVM_MSC_PREREQ(1800)
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# define LLVM_HAS_VARIADIC_TEMPLATES 1
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#else
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# define LLVM_HAS_VARIADIC_TEMPLATES 0
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#endif
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/// Expands to '&' if r-value references are supported.
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///
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/// This can be used to provide l-value/r-value overrides of member functions.
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/// The r-value override should be guarded by LLVM_HAS_RVALUE_REFERENCE_THIS
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#if LLVM_HAS_RVALUE_REFERENCE_THIS
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#define LLVM_LVALUE_FUNCTION &
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#else
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#define LLVM_LVALUE_FUNCTION
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#endif
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/// LLVM_DELETED_FUNCTION - Expands to = delete if the compiler supports it.
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/// Use to mark functions as uncallable. Member functions with this should
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/// be declared private so that some behavior is kept in C++03 mode.
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///
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/// class DontCopy {
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/// private:
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/// DontCopy(const DontCopy&) LLVM_DELETED_FUNCTION;
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/// DontCopy &operator =(const DontCopy&) LLVM_DELETED_FUNCTION;
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/// public:
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/// ...
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/// };
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#if __has_feature(cxx_deleted_functions) || \
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defined(__GXX_EXPERIMENTAL_CXX0X__) || LLVM_MSC_PREREQ(1800)
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#define LLVM_DELETED_FUNCTION = delete
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#else
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#define LLVM_DELETED_FUNCTION
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#endif
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#if __has_feature(cxx_constexpr) || defined(__GXX_EXPERIMENTAL_CXX0X__)
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# define LLVM_CONSTEXPR constexpr
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#else
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# define LLVM_CONSTEXPR
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#endif
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/// LLVM_LIBRARY_VISIBILITY - If a class marked with this attribute is linked
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/// into a shared library, then the class should be private to the library and
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/// not accessible from outside it. Can also be used to mark variables and
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/// functions, making them private to any shared library they are linked into.
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/// On PE/COFF targets, library visibility is the default, so this isn't needed.
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#if (__has_attribute(visibility) || __GNUC_PREREQ(4, 0)) && \
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!defined(__MINGW32__) && !defined(__CYGWIN__) && !defined(LLVM_ON_WIN32)
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#define LLVM_LIBRARY_VISIBILITY __attribute__ ((visibility("hidden")))
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#else
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#define LLVM_LIBRARY_VISIBILITY
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#endif
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#if __has_attribute(used) || __GNUC_PREREQ(3, 1)
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#define LLVM_ATTRIBUTE_USED __attribute__((__used__))
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#else
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#define LLVM_ATTRIBUTE_USED
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#endif
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#if __has_attribute(warn_unused_result) || __GNUC_PREREQ(3, 4)
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#define LLVM_ATTRIBUTE_UNUSED_RESULT __attribute__((__warn_unused_result__))
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#else
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#define LLVM_ATTRIBUTE_UNUSED_RESULT
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#endif
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// Some compilers warn about unused functions. When a function is sometimes
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// used or not depending on build settings (e.g. a function only called from
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// within "assert"), this attribute can be used to suppress such warnings.
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//
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// However, it shouldn't be used for unused *variables*, as those have a much
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// more portable solution:
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// (void)unused_var_name;
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// Prefer cast-to-void wherever it is sufficient.
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#if __has_attribute(unused) || __GNUC_PREREQ(3, 1)
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#define LLVM_ATTRIBUTE_UNUSED __attribute__((__unused__))
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#else
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#define LLVM_ATTRIBUTE_UNUSED
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#endif
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// FIXME: Provide this for PE/COFF targets.
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#if (__has_attribute(weak) || __GNUC_PREREQ(4, 0)) && \
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(!defined(__MINGW32__) && !defined(__CYGWIN__) && !defined(LLVM_ON_WIN32))
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#define LLVM_ATTRIBUTE_WEAK __attribute__((__weak__))
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#else
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#define LLVM_ATTRIBUTE_WEAK
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#endif
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// Prior to clang 3.2, clang did not accept any spelling of
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// __has_attribute(const), so assume it is supported.
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#if defined(__clang__) || defined(__GNUC__)
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// aka 'CONST' but following LLVM Conventions.
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#define LLVM_READNONE __attribute__((__const__))
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#else
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#define LLVM_READNONE
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#endif
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#if __has_attribute(pure) || defined(__GNUC__)
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// aka 'PURE' but following LLVM Conventions.
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#define LLVM_READONLY __attribute__((__pure__))
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#else
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#define LLVM_READONLY
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#endif
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#if __has_builtin(__builtin_expect) || __GNUC_PREREQ(4, 0)
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#define LLVM_LIKELY(EXPR) __builtin_expect((bool)(EXPR), true)
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#define LLVM_UNLIKELY(EXPR) __builtin_expect((bool)(EXPR), false)
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#else
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#define LLVM_LIKELY(EXPR) (EXPR)
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#define LLVM_UNLIKELY(EXPR) (EXPR)
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#endif
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// C++ doesn't support 'extern template' of template specializations. GCC does,
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// but requires __extension__ before it. In the header, use this:
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// EXTERN_TEMPLATE_INSTANTIATION(class foo<bar>);
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// in the .cpp file, use this:
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// TEMPLATE_INSTANTIATION(class foo<bar>);
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#ifdef __GNUC__
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#define EXTERN_TEMPLATE_INSTANTIATION(X) __extension__ extern template X
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#define TEMPLATE_INSTANTIATION(X) template X
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#else
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#define EXTERN_TEMPLATE_INSTANTIATION(X)
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#define TEMPLATE_INSTANTIATION(X)
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#endif
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/// LLVM_ATTRIBUTE_NOINLINE - On compilers where we have a directive to do so,
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/// mark a method "not for inlining".
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#if __has_attribute(noinline) || __GNUC_PREREQ(3, 4)
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#define LLVM_ATTRIBUTE_NOINLINE __attribute__((noinline))
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#elif defined(_MSC_VER)
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#define LLVM_ATTRIBUTE_NOINLINE __declspec(noinline)
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#else
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#define LLVM_ATTRIBUTE_NOINLINE
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#endif
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/// LLVM_ATTRIBUTE_ALWAYS_INLINE - On compilers where we have a directive to do
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/// so, mark a method "always inline" because it is performance sensitive. GCC
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/// 3.4 supported this but is buggy in various cases and produces unimplemented
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/// errors, just use it in GCC 4.0 and later.
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#if __has_attribute(always_inline) || __GNUC_PREREQ(4, 0)
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#define LLVM_ATTRIBUTE_ALWAYS_INLINE inline __attribute__((always_inline))
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#elif defined(_MSC_VER)
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#define LLVM_ATTRIBUTE_ALWAYS_INLINE __forceinline
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#else
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#define LLVM_ATTRIBUTE_ALWAYS_INLINE
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#endif
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#ifdef __GNUC__
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#define LLVM_ATTRIBUTE_NORETURN __attribute__((noreturn))
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#elif defined(_MSC_VER)
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#define LLVM_ATTRIBUTE_NORETURN __declspec(noreturn)
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#else
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#define LLVM_ATTRIBUTE_NORETURN
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#endif
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#if __has_attribute(returns_nonnull) || __GNUC_PREREQ(4, 9)
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#define LLVM_ATTRIBUTE_RETURNS_NONNULL __attribute__((returns_nonnull))
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#else
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#define LLVM_ATTRIBUTE_RETURNS_NONNULL
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#endif
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/// LLVM_EXTENSION - Support compilers where we have a keyword to suppress
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/// pedantic diagnostics.
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#ifdef __GNUC__
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#define LLVM_EXTENSION __extension__
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#else
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#define LLVM_EXTENSION
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#endif
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// LLVM_ATTRIBUTE_DEPRECATED(decl, "message")
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#if __has_feature(attribute_deprecated_with_message)
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# define LLVM_ATTRIBUTE_DEPRECATED(decl, message) \
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decl __attribute__((deprecated(message)))
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#elif defined(__GNUC__)
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# define LLVM_ATTRIBUTE_DEPRECATED(decl, message) \
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decl __attribute__((deprecated))
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#elif defined(_MSC_VER)
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# define LLVM_ATTRIBUTE_DEPRECATED(decl, message) \
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__declspec(deprecated(message)) decl
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#else
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# define LLVM_ATTRIBUTE_DEPRECATED(decl, message) \
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decl
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#endif
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/// LLVM_BUILTIN_UNREACHABLE - On compilers which support it, expands
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/// to an expression which states that it is undefined behavior for the
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/// compiler to reach this point. Otherwise is not defined.
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#if __has_builtin(__builtin_unreachable) || __GNUC_PREREQ(4, 5)
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# define LLVM_BUILTIN_UNREACHABLE __builtin_unreachable()
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#elif defined(_MSC_VER)
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# define LLVM_BUILTIN_UNREACHABLE __assume(false)
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#endif
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/// LLVM_BUILTIN_TRAP - On compilers which support it, expands to an expression
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/// which causes the program to exit abnormally.
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#if __has_builtin(__builtin_trap) || __GNUC_PREREQ(4, 3)
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# define LLVM_BUILTIN_TRAP __builtin_trap()
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#else
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# define LLVM_BUILTIN_TRAP *(volatile int*)0x11 = 0
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#endif
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/// \macro LLVM_ASSUME_ALIGNED
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/// \brief Returns a pointer with an assumed alignment.
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#if __has_builtin(__builtin_assume_aligned) && __GNUC_PREREQ(4, 7)
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# define LLVM_ASSUME_ALIGNED(p, a) __builtin_assume_aligned(p, a)
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#elif defined(LLVM_BUILTIN_UNREACHABLE)
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// As of today, clang does not support __builtin_assume_aligned.
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# define LLVM_ASSUME_ALIGNED(p, a) \
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(((uintptr_t(p) % (a)) == 0) ? (p) : (LLVM_BUILTIN_UNREACHABLE, (p)))
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#else
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# define LLVM_ASSUME_ALIGNED(p, a) (p)
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#endif
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/// \macro LLVM_FUNCTION_NAME
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/// \brief Expands to __func__ on compilers which support it. Otherwise,
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/// expands to a compiler-dependent replacement.
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#if defined(_MSC_VER)
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# define LLVM_FUNCTION_NAME __FUNCTION__
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#else
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# define LLVM_FUNCTION_NAME __func__
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#endif
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/// \macro LLVM_MEMORY_SANITIZER_BUILD
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/// \brief Whether LLVM itself is built with MemorySanitizer instrumentation.
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#if __has_feature(memory_sanitizer)
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# define LLVM_MEMORY_SANITIZER_BUILD 1
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# include <sanitizer/msan_interface.h>
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#else
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# define LLVM_MEMORY_SANITIZER_BUILD 0
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# define __msan_allocated_memory(p, size)
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# define __msan_unpoison(p, size)
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#endif
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/// \macro LLVM_ADDRESS_SANITIZER_BUILD
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/// \brief Whether LLVM itself is built with AddressSanitizer instrumentation.
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#if __has_feature(address_sanitizer) || defined(__SANITIZE_ADDRESS__)
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# define LLVM_ADDRESS_SANITIZER_BUILD 1
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#else
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# define LLVM_ADDRESS_SANITIZER_BUILD 0
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#endif
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/// \macro LLVM_IS_UNALIGNED_ACCESS_FAST
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/// \brief Is unaligned memory access fast on the host machine.
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///
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/// Don't specialize on alignment for platforms where unaligned memory accesses
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/// generates the same code as aligned memory accesses for common types.
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#if defined(_M_AMD64) || defined(_M_IX86) || defined(__amd64) || \
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defined(__amd64__) || defined(__x86_64) || defined(__x86_64__) || \
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defined(_X86_) || defined(__i386) || defined(__i386__)
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# define LLVM_IS_UNALIGNED_ACCESS_FAST 1
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#else
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# define LLVM_IS_UNALIGNED_ACCESS_FAST 0
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#endif
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/// \macro LLVM_EXPLICIT
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/// \brief Expands to explicit on compilers which support explicit conversion
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/// operators. Otherwise expands to nothing.
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#if __has_feature(cxx_explicit_conversions) || \
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defined(__GXX_EXPERIMENTAL_CXX0X__) || LLVM_MSC_PREREQ(1800)
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#define LLVM_EXPLICIT explicit
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#else
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#define LLVM_EXPLICIT
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#endif
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/// \brief Does the compiler support generalized initializers (using braced
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/// lists and std::initializer_list). While clang may claim it supports general
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/// initializers, if we're using MSVC's headers, we might not have a usable
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/// std::initializer list type from the STL. Disable this for now.
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#if __has_feature(cxx_generalized_initializers) && !defined(_MSC_VER)
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#define LLVM_HAS_INITIALIZER_LISTS 1
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#else
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#define LLVM_HAS_INITIALIZER_LISTS 0
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#endif
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/// \brief Mark debug helper function definitions like dump() that should not be
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/// stripped from debug builds.
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// FIXME: Move this to a private config.h as it's not usable in public headers.
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#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
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#define LLVM_DUMP_METHOD LLVM_ATTRIBUTE_NOINLINE LLVM_ATTRIBUTE_USED
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#else
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#define LLVM_DUMP_METHOD LLVM_ATTRIBUTE_NOINLINE
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#endif
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#endif
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