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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 ------- 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 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 ------- (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 ` (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
end of thread, other threads:[~2005-09-10 2:33 UTC | newest] Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 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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