Question on -fopt-info-inline

[Jeff Law]

On 07/03/2018 12:28 PM, Qing Zhao wrote:
> 
>>>
>>>>
>>>> In order to collect complete information on all the inlining
>>>> transformation that GCC applies on a given program,
>>>> I searched online, and found that the option -fopt-info-inline might be
>>>> the right option to use:
>>>>
>>>> https://gcc.gnu.org/onlinedocs/gcc/Developer-Options.html <https://gcc.gnu.org/onlinedocs/gcc/Developer-Options.html> <https://gcc.gnu.org/onlinedocs/gcc/Developer-Options.html <https://gcc.gnu.org/onlinedocs/gcc/Developer-Options.html>>
>>>> <https://gcc.gnu.org/onlinedocs/gcc/Developer-Options.html <https://gcc.gnu.org/onlinedocs/gcc/Developer-Options.html>>
>>>>
>>>> in which, it mentioned:
>>>>
>>>> "As another example,
>>>> gcc -O3 -fopt-info-inline-optimized-missed=inline.txt
>>>> outputs information about missed optimizations as well as optimized
>>>> locations from all the inlining passes into inline.txt. 
>>>>
>>>> “
>>>>
>>>> Then I checked a very small testcase with GCC9 as following:
>>>>
>>>> [qinzhao@localhost inline_report]$ cat inline_1.c
>>>> static int foo (int a)
>>>> {
>>>> return a + 10;
>>>> }
>>>>
>>>> static int bar (int b)
>>>> {
>>>> return b - 20;
>>>> }
>>>>
>>>> static int boo (int a, int b)
>>>> {
>>>> return foo (a) + bar (b);
>>>> }
>>>>
>>>> extern int v_a, v_b;
>>>> extern int result;
>>>>
>>>> int compute ()
>>>> {
>>>> result = boo (v_a, v_b);
>>>> return result; 
>>>> }
>>>>
>>>> [qinzhao@localhost inline_report]$ /home/qinzhao/Install/latest/bin/gcc
>>>> -O3 -fopt-info-inline-optimized-missed=inline.txt inline_1.c -S
>>>> [qinzhao@localhost inline_report]$ ls -l inline.txt
>>>> -rw-rw-r--. 1 qinzhao qinzhao 0 Jul  3 11:25 inline.txt
>>>> [qinzhao@localhost inline_report]$ cat inline_1.s
>>>> 	.file	"inline_1.c"
>>>> 	.text
>>>> 	.p2align 4,,15
>>>> 	.globl	compute
>>>> 	.type	compute, @function
>>>> compute:
>>>> .LFB3:
>>>> 	.cfi_startproc
>>>> 	movl	v_a(%rip), %edx
>>>> 	movl	v_b(%rip), %eax
>>>> 	leal	-10(%rdx,%rax), %eax
>>>> 	movl	%eax, result(%rip)
>>>> 	ret
>>>> 	.cfi_endproc
>>>> .LFE3:
>>>> 	.size	compute, .-compute
>>>> 	.ident	"GCC: (GNU) 9.0.0 20180702 (experimental)"
>>>> 	.section	.note.GNU-stack,"",@progbits
>>>>
>>>> From the above, we can see:
>>>> 1. the call chains to —>“boo”->”foo”, “bar” in the routine “compute”
>>>> are completely inlined into “compute”;
>>>> 2. However, there is NO any inline information is dumped into
>>>> “inline.txt”.
>>>>
>>>>
>>>> So, My questions are:
>>>>
>>>> 1. Is the option -fopt-info-inline  the right option to use to get the
>>>> complete inlining transformation info from GCC?
>>>> 2. is this a bug that the current -fopt-info-inline cannot dump
>>>> anything for this testing case?
>>>
>>> I think the early inliner doesn't use opt-info yet. 
>>
>> so, shall we add the opt-info support to early inliner?
> 
> I just created the following PR to record this work:
> 
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86395 <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86395>
> 
> let me know if I missed anything.
I'm hoping that the work David is doing WRT optimization information
will be usable for the inliner as well.  In fact, inlining and
vectorization are the two use cases we identified internally as the
first targets.


jeff