https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87268
Bug ID: 87268
Summary: Missed optimization for a tailcall
Product: gcc
Version: 8.2.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: no...@turm-lahnstein.de
Target Milestone: ---
For a simple code like this:
extern int shared;
void doit(int *);
int call_doit(){
doit(&shared);
}
when compiled with -O3 the resulting assembler is without tailcall
optimization:
call_doit:
subq $8, %rsp
movl $shared, %edi
call doit
addq $8, %rsp
ret
There are two thing that are probably not needed:
1. The whole "subq $8, %rsp / addq $8, %rsp" is not really necessary,
isn't it?
2. call instead of simple jmp, which would be possible due to tailcall
optimization. Possibly it was not performed, because subq/addq are still
hanging around.
If I'm not mistaken, something like:
call_doit:
movl $global, %edi
jmp doit
should be possible as output.
