Date: Thu, 28 Jan 1999 17:29:57 -0800 (PST) From: Matthew Dillon <dillon@apollo.backplane.com> To: Steve Kargl <sgk@troutmask.apl.washington.edu> Cc: peter.jeremy@auss2.alcatel.com.au, current@FreeBSD.ORG Subject: Re: indent(1) and style(9) (was: btokup() macro in sys/malloc.h) Message-ID: <199901290129.RAA16381@apollo.backplane.com> References: <199901290122.RAA27878@troutmask.apl.washington.edu>
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:>
:> More then judicious use -- inlines are an incredible advantage. Most
:> people don't realize that GCC will optimize constant arguments through
:> an inline call. Try this:
:>
:> static __inline
Yah, and if it's static it will not even output code for fubar.
I've never trusted -O3, though, and you can't put static procedures
in header files ( because then you can't fall back to -O2 ). Thus,
for this sort of optimization to work the procedure must be in the same
source file, which kills the modularity. Also, on top of all of that,
GCC may not make a good decision on whether to actually inline the
static or whether to call it - it might wind up inlining a large
routine that you call many times in your module and both bloat the code
and destroy the L1 cache.
I think it's better to make things explicitly __inline and to put them in
the proper subsystem's header files. It isn't worth depending on -O3
for things to compile:
-O3 Optimize yet more. This turns on everything -O2
does, along with also turning on -finline-func-
tions.
-Matt
:Matt,
:
:int
:fubar(int c)
:{
: if (c & 1)
: ++c;
: if (c & 2)
: ++c;
: return(c);
:}
:
:void
:fubar2(void)
:{
: volatile int x;
:
: x = fubar(0);
: x = fubar(1);
: x = fubar(2);
: x = fubar(3);
:}
:
:% cc -S -O3 x.c
:% cat x.s
:
:fubar2:
: pushl %ebp
: movl %esp,%ebp
: subl $4,%esp
: xorl %eax,%eax <----- fubar (0)
: movl %eax,-4(%ebp)
: movl $3,-4(%ebp) <----- fubar (1)
: movl $3,-4(%ebp) <----- fubar (2)
: movl $4,-4(%ebp) <----- fubar (3)
: leave
: ret
:
:--
:Steve
:
:finger kargl@troutmask.apl.washington.edu
:http://troutmask.apl.washington.edu/~clesceri/kargl.html
:
Matthew Dillon
<dillon@backplane.com>
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