https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111088
Bug ID: 111088
Summary: useless 'xor eax,eax' inserted when a value is not
returned.
Product: gcc
Version: 13.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: charly.poyac at gmail dot com
Target Milestone: ---
I compile this simple C code with GCC 13.2:
int foo(int *a)
{
*a += 1;
}
int foo2(int *a)
{
*a += 1;
}
and it produces the following assembly code with '-O3':
foo:
add DWORD PTR [rdi], 1
ret
foo2:
add DWORD PTR [rdi], 1
xor eax, eax
ret
see godbolt: https://godbolt.org/z/eeT63ePcr
We can see the inconsistency between the two functions with the 'xor eax,eax'
added in foo2. This does not happen if I compile with -O1.
Yes, these functions should return an integer, but they don't. However, this is
allowed by the C standard (2018 6.9.1 11/12).
