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Commit02a6a54

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Make use of compiler builtins and/or assembly for CLZ, CTZ, POPCNT.
Test for the compiler builtins __builtin_clz, __builtin_ctz, and__builtin_popcount, and make use of these in preference tohandwritten C code if they're available. Create src/portinfrastructure for "leftmost one", "rightmost one", and "popcount"so as to centralize these decisions.On x86_64, __builtin_popcount generally won't make use of the POPCNTopcode because that's not universally supported yet. Provide codethat checks CPUID and then calls POPCNT via asm() if available.This requires indirecting through a function pointer, which isan annoying amount of overhead for a one-instruction operation,but it's probably not worth working harder than this for ourcurrent use-cases.I'm not sure we've found all the existing places that could profitfrom this new infrastructure; but we at least touched all theones that used copied-and-pasted versions of the bitmapset.c code,and got rid of multiple copies of the associated constant arrays.While at it, replace c-compiler.m4's one-per-builtin-functionmacros with a single one that can handle all the cases we needto worry about so far. Also, because I'm paranoid, make thosechecks into AC_LINK checks rather than just AC_COMPILE; theformer coding failed to verify that libgcc has support for thebuiltin, in cases where it's not inline code.David Rowley, Thomas Munro, Alvaro Herrera, Tom LaneDiscussion:https://postgr.es/m/CAKJS1f9WTAGG1tPeJnD18hiQW5gAk59fQ6WK-vfdAKEHyRg2RA@mail.gmail.com
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‎config/c-compiler.m4

Lines changed: 27 additions & 54 deletions
Original file line numberDiff line numberDiff line change
@@ -273,60 +273,6 @@ AC_DEFINE(HAVE__BUILTIN_TYPES_COMPATIBLE_P, 1,
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fi])# PGAC_C_TYPES_COMPATIBLE
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# PGAC_C_BUILTIN_BSWAP16
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# -------------------------
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# Check if the C compiler understands __builtin_bswap16(),
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# and define HAVE__BUILTIN_BSWAP16 if so.
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AC_DEFUN([PGAC_C_BUILTIN_BSWAP16],
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[AC_CACHE_CHECK(for__builtin_bswap16,pgac_cv__builtin_bswap16,
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[AC_COMPILE_IFELSE([AC_LANG_SOURCE(
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[static unsigned long int x = __builtin_bswap16(0xaabb);]
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)],
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[pgac_cv__builtin_bswap16=yes],
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[pgac_cv__builtin_bswap16=no])])
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if test x"$pgac_cv__builtin_bswap16" = xyes ; then
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AC_DEFINE(HAVE__BUILTIN_BSWAP16,1,
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[Define to 1 if your compiler understands __builtin_bswap16.])
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fi])# PGAC_C_BUILTIN_BSWAP16
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# PGAC_C_BUILTIN_BSWAP32
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# -------------------------
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# Check if the C compiler understands __builtin_bswap32(),
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# and define HAVE__BUILTIN_BSWAP32 if so.
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AC_DEFUN([PGAC_C_BUILTIN_BSWAP32],
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[AC_CACHE_CHECK(for__builtin_bswap32,pgac_cv__builtin_bswap32,
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[AC_COMPILE_IFELSE([AC_LANG_SOURCE(
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[static unsigned long int x = __builtin_bswap32(0xaabbccdd);]
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)],
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[pgac_cv__builtin_bswap32=yes],
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[pgac_cv__builtin_bswap32=no])])
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if test x"$pgac_cv__builtin_bswap32" = xyes ; then
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AC_DEFINE(HAVE__BUILTIN_BSWAP32,1,
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[Define to 1 if your compiler understands __builtin_bswap32.])
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fi])# PGAC_C_BUILTIN_BSWAP32
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# PGAC_C_BUILTIN_BSWAP64
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# -------------------------
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# Check if the C compiler understands __builtin_bswap64(),
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# and define HAVE__BUILTIN_BSWAP64 if so.
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AC_DEFUN([PGAC_C_BUILTIN_BSWAP64],
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[AC_CACHE_CHECK(for__builtin_bswap64,pgac_cv__builtin_bswap64,
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[AC_COMPILE_IFELSE([AC_LANG_SOURCE(
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[static unsigned long int x = __builtin_bswap64(0xaabbccddeeff0011);]
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)],
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[pgac_cv__builtin_bswap64=yes],
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[pgac_cv__builtin_bswap64=no])])
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if test x"$pgac_cv__builtin_bswap64" = xyes ; then
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AC_DEFINE(HAVE__BUILTIN_BSWAP64,1,
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[Define to 1 if your compiler understands __builtin_bswap64.])
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fi])# PGAC_C_BUILTIN_BSWAP64
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# PGAC_C_BUILTIN_CONSTANT_P
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# -------------------------
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# Check if the C compiler understands __builtin_constant_p(),
@@ -423,6 +369,33 @@ fi])# PGAC_C_COMPUTED_GOTO
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# PGAC_CHECK_BUILTIN_FUNC
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# -----------------------
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# This is similar to AC_CHECK_FUNCS(), except that it will work for compiler
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# builtin functions, as that usually fails to.
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# The first argument is the function name, eg [__builtin_clzl], and the
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# second is its argument list, eg [unsigned long x]. The current coding
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# works only for a single argument named x; we might generalize that later.
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# It's assumed that the function's result type is coercible to int.
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# On success, we define "HAVEfuncname" (there's usually more than enough
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# underscores already, so we don't add another one).
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AC_DEFUN([PGAC_CHECK_BUILTIN_FUNC],
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[AC_CACHE_CHECK(for$1,pgac_cv$1,
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[AC_LINK_IFELSE([AC_LANG_PROGRAM([
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int
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call$1($2)
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{
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return$1(x);
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}],[])],
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[pgac_cv$1=yes],
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[pgac_cv$1=no])])
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if test x"${pgac_cv$1}" = xyes ; then
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AC_DEFINE_UNQUOTED(AS_TR_CPP([HAVE$1]),1,
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[Define to 1 if your compiler understands$1.])
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fi])# PGAC_CHECK_BUILTIN_FUNC
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# PGAC_PROG_VARCC_VARFLAGS_OPT
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# -----------------------
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# Given a compiler, variable name and a string, check if the compiler

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