On 2017-09-28 18:39:03 -0400, Tom Lane wrote: > Andres Freund <and...@anarazel.de> writes: > > On 2017-09-28 16:21:34 -0400, Tom Lane wrote: > >> We could save a pointless register spill > >> and reload if there were a temporary variable in there, > > > Makes sense. Do you want to make it so, or shall I? > > I just finished testing a patch, as attached. On my machine (again, > not latest gcc: 4.4.7 on RHEL6 x86_64), it reduces the code size of > execExprInterp.o by a fraction of a percent, and it seems to offer > a slight benefit in "pgbench -S" performance although I'd not put > much stock in that being reproducible.
Cool. > + * Note: the reason for using a temporary variable "d", here > and in > + * other places, is that some compilers think "*op->resvalue = > f();" > + * requires them to evaluate op->resvalue into a register before > + * calling f(), just in case f() is able to modify op->resvalue > + * somehow. The extra line of code can save a useless register > spill > + * and reload, on architectures without many registers. I'd remove the "without many registers" bit - that's really more an functioncall ABI question (#caller vs #callee saved registers) than about the actual architecture. Greetings, Andres Freund -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
