A few macros and functions to exploit compiler specific optimizations. More...

Detailed Description

A few macros and functions to exploit compiler specific optimizations.

This file contains a few macros and functions analogous to linux/compiler.h

Example: likely/unlikely macros: For example, Linux kernel wraps GCC's __builtin_expect as follows.
// from linux/compiler.h.

#define likely(x) __builtin_expect(!!(x), 1)

#define unlikely(x) __builtin_expect(!!(x), 0)

...

if (likely(var == 42)) {

...

}

We provide macros/functions to do equivalent optimizations here. However, we should minimize the use of such detailed and custom optimizations. In general, compiler is good enough to predict branches/inlining, and, even if it isn't, we should rather use -fprofile-arcs. So far, we use it only for a few places that are VERY important and VERY easy to predict by human.

See also: http://blog.man7.org/2012/10/how-much-do-builtinexpect-likely-and.html

Collaboration diagram for Compiler Specific Optimizations:

Modules
	Memorandum on ARMv8 (AArch64) Support
	We keep notes on FOEDUS's ARMv8 (AArch64) Support here.

Macros
#define	LIKELY(x) __builtin_expect(!!(x), 1)
	Hints that x is highly likely true. More...

#define	UNLIKELY(x) __builtin_expect(!!(x), 0)
	Hints that x is highly likely false. More...

#define	NO_INLINE __attribute__((noinline))
	A function suffix to hint that the function should never be inlined. More...

#define	ALWAYS_INLINE __attribute__((always_inline))
	A function suffix to hint that the function should always be inlined. More...

#define	ASSUME_ALIGNED(x, y) __builtin_assume_aligned(x, y)
	Wraps GCC's __builtin_assume_aligned. More...

#define	MAY_ALIAS __attribute__((__may_alias__))
	Wraps GCC's attribute((may_alias)). More...

#define	RESTRICT_ALIAS __restrict
	Wraps GCC's __restrict. More...

Macro Definition Documentation

#define ALWAYS_INLINE __attribute__((always_inline))

A function suffix to hint that the function should always be inlined.

GCC's always_inline.

Definition at line 106 of file compiler.hpp.

#define ASSUME_ALIGNED	(	x,
		y
	)	__builtin_assume_aligned(x, y)

Wraps GCC's __builtin_assume_aligned.

Definition at line 111 of file compiler.hpp.

Referenced by foedus::storage::hash::HashInsertLogType::apply_record(), foedus::storage::hash::HashUpdateLogType::apply_record(), foedus::storage::masstree::MasstreeCommonLogType::apply_record_prepare(), foedus::storage::masstree::MasstreeCursor::copy_combined_key(), foedus::storage::masstree::copy_input_key(), foedus::storage::masstree::count_common_slices(), foedus::storage::hash::HashDataPage::create_record_in_snapshot(), foedus::cache::CacheHashtable::evict_main_loop(), foedus::storage::masstree::MasstreeCommonLogType::get_payload(), foedus::assorted::read_bigendian(), and foedus::assorted::write_bigendian().

#define LIKELY ( x ) __builtin_expect(!!(x), 1)

Hints that x is highly likely true.

GCC's __builtin_expect.

Definition at line 103 of file compiler.hpp.

Referenced by foedus::ErrorStack::append_custom_message(), foedus::storage::masstree::MasstreeCommonLogType::compare_logs(), foedus::ErrorStack::copy_custom_message(), foedus::ErrorStack::ErrorStack(), foedus::cache::CacheHashtable::evict_main_loop(), foedus::storage::array::ArrayComposeContext::execute(), foedus::storage::hash::HashComposeContext::execute(), foedus::storage::masstree::MasstreeComposeContext::execute(), foedus::storage::masstree::MasstreeStoragePimpl::find_border_physical(), foedus::storage::masstree::MasstreeBorderPage::find_key(), foedus::storage::masstree::MasstreeBorderPage::find_key_for_reserve(), foedus::storage::sequential::SequentialRecordIterator::next(), foedus::storage::hash::ComposedBinsBuffer::next_bin(), foedus::ErrorStack::operator=(), foedus::storage::masstree::MasstreeStoragePimpl::peek_volatile_page_boundaries_next_layer(), foedus::storage::masstree::MasstreeStoragePimpl::peek_volatile_page_boundaries_this_layer_recurse(), foedus::storage::hash::HashDataPage::search_key_physical(), foedus::ErrorStack::verify(), and foedus::ErrorStack::~ErrorStack().

#define MAY_ALIAS __attribute__((__may_alias__))

Wraps GCC's attribute((may_alias)).

This is QUITE important for us. This keyword is not for performance but for correctness. I'm seeing weird behaviors even with -fno-strict-aliasing. This keyword might help. Otherwise, we have to memcpy to type-pun everything. uggggrrr.

Definition at line 107 of file compiler.hpp.

#define NO_INLINE __attribute__((noinline))

A function suffix to hint that the function should never be inlined.

GCC's noinline.

Definition at line 105 of file compiler.hpp.

#define RESTRICT_ALIAS __restrict

Wraps GCC's __restrict.

OTOH, this explicitly helps compiler auto-vectorize and do other stuffs, saying that the variable is never aliased in the function. Seems like older gcc ignored __restrict when fno-strict-aliasing is specified, but recent gcc doesn't.

Attention: DO NOT USE THIS if you don't know what __restrict means.

Definition at line 108 of file compiler.hpp.

#define UNLIKELY ( x ) __builtin_expect(!!(x), 0)

Hints that x is highly likely false.

GCC's __builtin_expect.

Definition at line 104 of file compiler.hpp.

Detailed Description

Modules

Macros

Macro Definition Documentation