Using exit() requires stdlib.h, which is not included.  Use return
instead.  Also add return type for main().
Reviewed-by: Heikki Linnakangas <hlinnaka@iki.fi>
Reviewed-by: Thomas Munro <thomas.munro@enterprisedb.com>

This is like BSWAP32, but for 64-bit values.  Since we've got two of
them now and they have use cases (like sortsupport) beyond CRCs, move
the definitions to their own header file.

Peter Geoghegan

With optimizations enabled at least one compiler, clang 3.7, optimized
away the crc intrinsics knowing that the result went on unused and has
no side effects. That can trigger errors in code generation when the
intrinsic is used, as we chose to use the intrinsics without any
additional compiler flag. Return the computed value to prevent that.

With some more pedantic warning flags (-Wold-style-definition) the
configure test failed to recognize the existence of _mm_crc32_u*
intrinsics due to an independent warning in the test because the test
turned on -Werror, but that's not actually needed here.

Discussion: 20150814092039.GH4955@awork2.anarazel.de
Backpatch: 9.5, where the use of crc intrinsics was integrated.

So far we have worked around the fact that some very old compilers do
not support 'inline' functions by only using inline functions
conditionally (or not at all). Since such compilers are very rare by
now, we have decided to rely on inline functions from 9.6 onwards.

To avoid breaking these old compilers inline is defined away when not
supported. That'll cause "function x defined but not used" type of
warnings, but since nobody develops on such compilers anymore that's
ok.

This change in policy will allow us to more easily employ inline
functions.

I chose to remove code previously conditional on PG_USE_INLINE as it
seemed confusing to have code dependent on a define that's always
defined.

Blacklisting of compilers, like in c53f7387, now has to be done
differently. A platform template can define PG_FORCE_DISABLE_INLINE to
force inline to be defined empty.

Discussion: 20150701161447.GB30708@awork2.anarazel.de

AC_TRY_COMPILE(...) -> AC_COMPILE_IFELSE([AC_LANG_PROGRAM(...)])
AC_TRY_LINK(...) -> AC_LINK_IFELSE([AC_LANG_PROGRAM(...)])
AC_TRY_RUN(...) -> AC_RUN_IFELSE([AC_LANG_PROGRAM(...)])
AC_LANG_SAVE/RESTORE -> AC_LANG_PUSH/POP
AC_DECL_SYS_SIGLIST -> AC_CHECK_DECLS(...) (per snippet in autoconf manual)

Also use AC_LANG_SOURCE instead of AC_LANG_PROGRAM, where the main()
function is not needed.

With these changes, autoconf -Wall doesn't complain anymore.

Andreas Karlsson

Eliminate the separate 'len' variable from the loops, and also use the 4
byte instruction. This shaves off a few more cycles. Even though this
routine that uses the special SSE 4.2 instructions is much faster than a
generic routine, it's still a hot spot, so let's make it as fast as
possible.

Change the configure test to not test _mm_crc32_u64. That variant is only
available in the 64-bit x86-64 architecture, not in 32-bit x86. Modify
pg_comp_crc32c_sse42 so that it only uses _mm_crc32_u64 on x86-64. With
these changes, the SSE accelerated CRC-32C implementation can also be used
on 32-bit x86 systems.

This also fixes the 32-bit MSVC build.

Modern x86 and x86-64 processors with SSE 4.2 support have special
instructions, crc32b and crc32q, for calculating CRC-32C. They greatly
speed up CRC calculation.

Whether the instructions can be used or not depends on the compiler and the
target architecture. If generation of SSE 4.2 instructions is allowed for
the target (-msse4.2 flag on gcc and clang), use them. If they are not
allowed by default, but the compiler supports the -msse4.2 flag to enable
them, compile just the CRC-32C function with -msse4.2 flag, and check at
runtime whether the processor we're running on supports it. If it doesn't,
fall back to the slicing-by-8 algorithm. (With the common defaults on
current operating systems, the runtime-check variant is what you get in
practice.)

Abhijit Menon-Sen, heavily modified by me, reviewed by Andres Freund.

We will, for the foreseeable future, not expose 128 bit datatypes to
SQL. But being able to use 128bit math will allow us, in a later patch,
to use 128bit accumulators for some aggregates; leading to noticeable
speedups over using numeric.

So far we only detect a gcc/clang extension that supports 128bit math,
but no 128bit literals, and no *printf support. We might want to expand
this in the future to further compilers; if there are any that that
provide similar support.

Discussion: 544BB5F1.50709@proxel.se
Author: Andreas Karlsson, with significant editorializing by me
Reviewed-By: Peter Geoghegan, Oskari Saarenmaa

This speeds up WAL generation and replay. The new algorithm is
significantly faster with large inputs, like full-page images or when
inserting wide rows. It is slower with tiny inputs, i.e. less than 10 bytes
or so, but the speedup with longer inputs more than make up for that. Even
small WAL records at least have 24 byte header in the front.

The output is identical to the current byte-at-a-time computation, so this
does not affect compatibility. The new algorithm is only used for the
CRC-32C variant, not the legacy version used in tsquery or the
"traditional" CRC-32 used in hstore and ltree. Those are not as performance
critical, and are usually only applied over small inputs, so it seems
better to not carry around the extra lookup tables to speed up those rare
cases.

Abhijit Menon-Sen

This eliminates gobs of "unrecognized format function type" warnings
under MinGW compilers predating GCC 4.4.

Several upcoming performance/scalability improvements require atomic
operations. This new API avoids the need to splatter compiler and
architecture dependent code over all the locations employing atomic
ops.

For several of the potential usages it'd be problematic to maintain
both, a atomics using implementation and one using spinlocks or
similar. In all likelihood one of the implementations would not get
tested regularly under concurrency. To avoid that scenario the new API
provides a automatic fallback of atomic operations to spinlocks. All
properties of atomic operations are maintained. This fallback -
obviously - isn't as fast as just using atomic ops, but it's not bad
either. For one of the future users the atomics ontop spinlocks
implementation was actually slightly faster than the old purely
spinlock using implementation. That's important because it reduces the
fear of regressing older platforms when improving the scalability for
new ones.

The API, loosely modeled after the C11 atomics support, currently
provides 'atomic flags' and 32 bit unsigned integers. If the platform
efficiently supports atomic 64 bit unsigned integers those are also
provided.

To implement atomics support for a platform/architecture/compiler for
a type of atomics 32bit compare and exchange needs to be
implemented. If available and more efficient native support for flags,
32 bit atomic addition, and corresponding 64 bit operations may also
be provided. Additional useful atomic operations are implemented
generically ontop of these.

The implementation for various versions of gcc, msvc and sun studio have
been tested. Additional existing stub implementations for
* Intel icc
* HUPX acc
* IBM xlc
are included but have never been tested. These will likely require
fixes based on buildfarm and user feedback.

As atomic operations also require barriers for some operations the
existing barrier support has been moved into the atomics code.

Author: Andres Freund with contributions from Oskari Saarenmaa
Reviewed-By: Amit Kapila, Robert Haas, Heikki Linnakangas and Álvaro Herrera
Discussion: CA+TgmoYBW+ux5-8Ja=Mcyuy8=VXAnVRHp3Kess6Pn3DMXAPAEA@mail.gmail.com,
    20131015123303.GH5300@awork2.anarazel.de,
    20131028205522.GI20248@awork2.anarazel.de

This test used to just define an unused static inline function and check
whether that causes a warning.  But newer clang versions warn about
unused static inline functions when defined inside a .c file, but not
when defined in an included header, which is the case we care about.
Change the test to cope.

Andres Freund

Ants Aasma and Jeff Davis

In commit 71450d7f, we added code to inform
suitably-intelligent compilers that ereport() doesn't return if the elevel
is ERROR or higher.  This patch extends that to elog(), and also fixes a
double-evaluation hazard that the previous commit created in ereport(),
as well as reducing the emitted code size.

The elog() improvement requires the compiler to support __VA_ARGS__, which
should be available in just about anything nowadays since it's required by
C99.  But our minimum language baseline is still C89, so add a configure
test for that.

The previous commit assumed that ereport's elevel could be evaluated twice,
which isn't terribly safe --- there are already counterexamples in xlog.c.
On compilers that have __builtin_constant_p, we can use that to protect the
second test, since there's no possible optimization gain if the compiler
doesn't know the value of elevel.  Otherwise, use a local variable inside
the macros to prevent double evaluation.  The local-variable solution is
inferior because (a) it leads to useless code being emitted when elevel
isn't constant, and (b) it increases the optimization level needed for the
compiler to recognize that subsequent code is unreachable.  But it seems
better than not teaching non-gcc compilers about unreachability at all.

Lastly, if the compiler has __builtin_unreachable(), we can use that
instead of abort(), resulting in a noticeable code savings since no
function call is actually emitted.  However, it seems wise to do this only
in non-assert builds.  In an assert build, continue to use abort(), so that
the behavior will be predictable and debuggable if the "impossible"
happens.

These changes involve making the ereport and elog macros emit do-while
statement blocks not just expressions, which forces small changes in
a few call sites.

Andres Freund, Tom Lane, Heikki Linnakangas

The former name was too likely to conflict with symbols from external
headers; and, as seen in recent buildfarm failures in member spoonbill,
it has now happened at least in plpython.

Currently, the macros only work with fairly recent gcc versions, but there
is room to expand them to other compilers that have comparable features.

Heavily revised and autoconfiscated version of a patch by Andres Freund.

This is reported to be necessary on some versions of that OS.  In service
of this, cause PGAC_PROG_CC_CFLAGS_OPT to reject switches that result in
compiler warnings, since on yet other versions of that OS, the switch does
nothing except provoke a warning.

Report and patch by Ibrar Ahmed, further tweaking by me.

at end of files.

Added a configure test for "long long" datatypes. So far this is only used in ecpg and replaces the old test that was kind of hackish.

compilers, by applying a configure check to see if the compiler will accept
an unreferenced "static inline foo ..." function without warnings.  It is
believed that such warnings are the only reason not to declare inlined
functions in headers, if the compiler understands "inline" at all.

Kurt Harriman

vintage Linux is even more broken than we realized: a link to libreadline
will succeed, and fail only at runtime.  It seems that an AC_TRY_RUN test
is the only reliable way to check whether this is really safe.  Per report
from Tatsuo.

libreadline.  What we will do for compatibility :-(

shared libraries.  We've tried this before and had problems with libreadline
not linking properly on some platforms, but that seems to be a libreadline
bug that may have been fixed by now.  In any case, it's early enough in the
8.4 devel cycle that we can afford to have some transient breakage while
we work out any portability problems.

On Darwin, we try -Wl,-dead_strip_dylibs, which seems to be the equivalent
incantation there.

uses of the long-deprecated float32 in contrib/seg; the definitions themselves
are still there, but no longer used.  fmgr/README updated to match.

I added a CREATE FUNCTION to account for existing seg_center() code in seg.c
too, and some tests for it and the neighbor functions.  At the same time,
remove checks for NULL which are not needed (because the functions are declared
STRICT).

I had to do some adjustments to contrib's btree_gist too.  The choices for
representation there are not ideal for changing the underlying types :-(

Original patch by Zoltan Boszormenyi, with some adjustments by me.

- Change configure.in to use Autoconf 2.61 and update generated files.
- Update build system and documentation to support now directory variables
  offered by Autoconf 2.61.
- Replace usages of PGAC_CHECK_ALIGNOF by AC_CHECK_ALIGNOF, now available
  in Autoconf 2.61.
- Drop our patched version of AC_C_INLINE, as Autoconf now has the change.

binary compiles, and adjust configure tests for AIX.

  -O2 -Wall -Wmissing-prototypes -Wpointer-arith

Check whether the version of GCC we are using supports any of:

  -Wdeclaration-after-statement
  -Wendif-labels
  -Wold-style-definition

And add the supported flags to CFLAGS.

-fno-strict-aliasing.

$Header: -> $PostgreSQL Changes ...

When --enable-debug is used, then the default CFLAGS for non-GCC is just
-g without -O.

Backpatch enhancement of Autoconf inline test that detects problems with
the HP C compiler.

option -fno-strict-aliasing is available.

rewritten and the protocol is changed, but most elog calls are still
elog calls.  Also, we need to contemplate mechanisms for controlling
all this functionality --- eg, how much stuff should appear in the
postmaster log?  And what API should libpq expose for it?

parts.  Standardize spelling of comments in pg_config.h.

separate macro.  Also add support for %I64d which is the way on Windows.

The code that checks for the 64-bit int type now gives more reasonable
results when cross-compiling: In that case we just take the compiler's
information and trust that the arithmetic works.  Disabling int64 is too
pessimistic.

calls with new or now-built-in versions.  Make sure that all
calls to AC_DEFINE have a third argument, for possible use of
autoheader in the future.

which include files to consider.  Should fix BeOS problems with int8 types.