Horton

Re: Inlining comparators as a performance optimisation

Greg Stark <stark@mit.edu>

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From: Greg Stark <stark@mit.edu>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Andrew Dunstan <andrew@dunslane.net>, Heikki Linnakangas <heikki.linnakangas@enterprisedb.com>, Peter Geoghegan <peter@2ndquadrant.com>, PG Hackers <pgsql-hackers@postgresql.org>
Date: 2011-09-21T16:35:41Z
Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Speed up conversion of signed integers to C strings.

  2. Remove some unnecessary tests of pgstat_track_counts.

  3. Remove cvs keywords from all files.

  4. Code cleanup for function prototypes: change two K&R-style prototypes

  5. Use Min() instead of min() in qsort, for consistency and to avoid

  6. pgindent run for 8.2.

  7. Switch over to using our own qsort() all the time, as has been proposed

On Wed, Sep 21, 2011 at 5:23 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> None of that stuff is inlinable or constant-foldable today, nor would it
> be with the patch that Peter was proposing AFAICS, because none of the
> flags will ever be compile time constant values.

I was referring to transformations like this which I believe compilers
are already capable of doing:

v = ...;
while (...)
  if (v) {
    if (a < b) ... else ....;
  } else {
    if (a > b) ... else ...;
  }

turning it into code that looks like:

if (v) {
 while (....)
   if (a<b) ... else ...;
} else {
  while (....)
    if (a>b) ... else ...;
}

which may not look like much -- especially with branch prediction --
but then it's much more likely to be able to unroll the loop and do
clever instruction scheduling and so on than if there's an extra
branch in the middle of the loop. But if there's a function call to an
external function called through a function pointer in the middle of
the loop then the whole endeavour would be for naught.



-- 
greg