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* [Bug c/23769] New: always inline short functions if inlining would be as small as non-inlined code
@ 2005-09-07 19:11 ash at onezero dot org
2005-09-07 19:14 ` [Bug middle-end/23769] " pinskia at gcc dot gnu dot org
` (4 more replies)
0 siblings, 5 replies; 6+ messages in thread
From: ash at onezero dot org @ 2005-09-07 19:11 UTC (permalink / raw)
To: gcc-bugs
I noticed when compiling with gcc -std=c99 -Winline that this function
inline uint16_t f(uint16_t x) { return x; }
wasn't getting inlined. Inlining is also not done even when the function is
attributed with "__attribute__ ((always_inline))", nor does inlining happen
when there no attributes at all. Maybe this function isn't getting inlined
because the compiler decided that it would involve in some sense "too much"
expansion in the caller.
Regardless of this particular case, I wonder if the following enhancement to
gcc would be worthwhile: always inline when it can be deduced that the code
with inlining would be no larger than the code without inlining, regardless of
the size of the caller in whatever representation is used at the time this
decision is being made.
For example, on many architectures, a call to a function that accepts an
argument and returns a value will use at least 3 instructions in the caller:
one to push the argument onto the stack, one to call the function, and one to
retrieve the return value from the function. So, if the function uses up to
three instructions to do its calculation, plus a return statement (with no
calculation in the return), then inlining will use no more instruction space
than not inlining. In these cases, inlining probably ought to be done so as to
create opportunities for further optimizations later, e.g., common
subexpression elimination. A more sophisticated determination could take into
account the number of arguments and other factors. This might be especially
helpful with C++ programs that have a lot of short methods.
At least, this is how it looks to me - if I am wrong, maybe someone could
educate me a bit or point me to some documentation where I can learn more about
how gcc's inlining works. If inlining is supposed to work this way already,
then I'll be happy to try to isolate the code further so that we have a small
fully compilable example.
I'm compiling with this:
gcc -o t.exe -DZCodeTest -g -DZAssert -D__GCC__ -std=c99 -O3 -pedantic -Werror -
Wall -W -I. -Wundef -Wshadow -Wpointer-arith -Wcast-qual -Wbad-function-cast -
Wwrite-strings -Wstrict-prototypes -Wmissing-prototypes -Wmissing-declarations -
Wredundant-decls -Wdisabled-optimization -Winline t.c
--
Summary: always inline short functions if inlining would be as
small as non-inlined code
Product: gcc
Version: 3.3.1
Status: UNCONFIRMED
Severity: enhancement
Priority: P2
Component: c
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: ash at onezero dot org
CC: gcc-bugs at gcc dot gnu dot org
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23769
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug middle-end/23769] always inline short functions if inlining would be as small as non-inlined code
2005-09-07 19:11 [Bug c/23769] New: always inline short functions if inlining would be as small as non-inlined code ash at onezero dot org
@ 2005-09-07 19:14 ` pinskia at gcc dot gnu dot org
2005-09-07 19:18 ` ash at onezero dot org
` (3 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: pinskia at gcc dot gnu dot org @ 2005-09-07 19:14 UTC (permalink / raw)
To: gcc-bugs
------- Additional Comments From pinskia at gcc dot gnu dot org 2005-09-07 19:14 -------
3.3.x is old and does not have the inlining improvements that went into 3.4.x. You might want to try
3.4.x or even 4.0.x. 4.1.x (the mainline) has better inlining still.
But without a full testcase, we won't know if this is fixed. I am thinking it is for 4.0.x or 4.1.x.
--
What |Removed |Added
----------------------------------------------------------------------------
Component|c |middle-end
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23769
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug middle-end/23769] always inline short functions if inlining would be as small as non-inlined code
2005-09-07 19:11 [Bug c/23769] New: always inline short functions if inlining would be as small as non-inlined code ash at onezero dot org
2005-09-07 19:14 ` [Bug middle-end/23769] " pinskia at gcc dot gnu dot org
@ 2005-09-07 19:18 ` ash at onezero dot org
2005-09-07 19:18 ` ash at onezero dot org
` (2 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: ash at onezero dot org @ 2005-09-07 19:18 UTC (permalink / raw)
To: gcc-bugs
------- Additional Comments From ash at onezero dot org 2005-09-07 19:18 -------
(Cygwin)
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23769
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug middle-end/23769] always inline short functions if inlining would be as small as non-inlined code
2005-09-07 19:11 [Bug c/23769] New: always inline short functions if inlining would be as small as non-inlined code ash at onezero dot org
2005-09-07 19:14 ` [Bug middle-end/23769] " pinskia at gcc dot gnu dot org
2005-09-07 19:18 ` ash at onezero dot org
@ 2005-09-07 19:18 ` ash at onezero dot org
2005-09-10 2:22 ` pinskia at gcc dot gnu dot org
2005-09-10 2:33 ` ash at onezero dot org
4 siblings, 0 replies; 6+ messages in thread
From: ash at onezero dot org @ 2005-09-07 19:18 UTC (permalink / raw)
To: gcc-bugs
------- Additional Comments From ash at onezero dot org 2005-09-07 19:18 -------
I'm on Cywin and couldn't find a later version of gcc - is there one somewhere
that I can use?
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23769
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug middle-end/23769] always inline short functions if inlining would be as small as non-inlined code
2005-09-07 19:11 [Bug c/23769] New: always inline short functions if inlining would be as small as non-inlined code ash at onezero dot org
` (2 preceding siblings ...)
2005-09-07 19:18 ` ash at onezero dot org
@ 2005-09-10 2:22 ` pinskia at gcc dot gnu dot org
2005-09-10 2:33 ` ash at onezero dot org
4 siblings, 0 replies; 6+ messages in thread
From: pinskia at gcc dot gnu dot org @ 2005-09-10 2:22 UTC (permalink / raw)
To: gcc-bugs
------- Additional Comments From pinskia at gcc dot gnu dot org 2005-09-10 02:22 -------
(In reply to comment #2)
> I'm on Cywin and couldn't find a later version of gcc - is there one somewhere
> that I can use?
Either you can compile one or I think cygwin has a couple of versions of GCC you can install.
--
What |Removed |Added
----------------------------------------------------------------------------
CC| |pinskia at gcc dot gnu dot
| |org
Status|UNCONFIRMED |WAITING
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23769
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug middle-end/23769] always inline short functions if inlining would be as small as non-inlined code
2005-09-07 19:11 [Bug c/23769] New: always inline short functions if inlining would be as small as non-inlined code ash at onezero dot org
` (3 preceding siblings ...)
2005-09-10 2:22 ` pinskia at gcc dot gnu dot org
@ 2005-09-10 2:33 ` ash at onezero dot org
4 siblings, 0 replies; 6+ messages in thread
From: ash at onezero dot org @ 2005-09-10 2:33 UTC (permalink / raw)
To: gcc-bugs
------- Additional Comments From ash at onezero dot org 2005-09-10 02:33 -------
Yes, I'm running the most recent one of those. The discussion in the cygwin
lists does not make it appear that it is easy to compile and install gcc.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23769
^ permalink raw reply [flat|nested] 6+ messages in thread
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2005-09-07 19:11 [Bug c/23769] New: always inline short functions if inlining would be as small as non-inlined code ash at onezero dot org
2005-09-07 19:14 ` [Bug middle-end/23769] " pinskia at gcc dot gnu dot org
2005-09-07 19:18 ` ash at onezero dot org
2005-09-07 19:18 ` ash at onezero dot org
2005-09-10 2:22 ` pinskia at gcc dot gnu dot org
2005-09-10 2:33 ` ash at onezero dot org
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