Question on -fopt-info-inline

[Qing Zhao]

>> 
>>> 
>>> 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.

thanks.

Qing