https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111786
Bug ID: 111786
Summary: No tail recursion for simple program
Product: gcc
Version: 13.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: [email protected]
Target Milestone: ---
Created attachment 56096
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=56096&action=edit
C code of expr_main
Follow up with nearly the same source file as 111643, only without the flatten
attribute. Sorry for taking so long for that. I learned the optimized compiler
should output a tail recursion. But this seams not to be the case: With "sub"
and "call", 16 bytes on the stack are used.
The file attached file contains:
---
int expr_main(int argc, char **argv)
{
return expr_main_original(argc, argv);
}
---
And after cc1 -O3 on amd64, the output contains:
-- gcc 13.2.0 --
expr_main:
subq $8, %rsp
call expr_main_original
---
-- gcc 9.4.0 shipped with ubuntu 20.04 ---
expr_main:
endbr64
pushq %rax
popq %rax
pushq %rax
call expr_main_original
---
-- Expected --
expr_main:
jmp expr_main_original
---
If I compile the above snippet only, I get the expected result. But not when
compiling the whole C file which also includes the body of
expr_main_original(). I also suspect there are some other factors I don't know,
since many other functions I tested yield the expected result.
In my case, the overhead seams to be negligible. However, I think it should be
possible to construct similar recursive programs where the overhead compared to
tail recursion is not negligible.
