https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97968
Bug ID: 97968
Summary: Unnecessary mov instruction with comparison and cmov
Product: gcc
Version: 11.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: rtl-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: denis.campredon at gmail dot com
Target Milestone: ---
The same problem applies with all comparison operators but '==' for 'int' and
'long' on x86-64.
(Returning a negative value instead of 0 makes the compiler generate a jump
instead of a cmov. I don't know if it's worth a bug)
-------------------
int f(int n, int j)
{
return n > j ? n : 0;
}
-------------------
with O2 produces
-------------------
f(int, int):
mov eax, edi
cmp edi, esi
mov edx, 0
cmovle eax, edx
ret
-------------------
Ideally it should produce something like that. (the first mov can be deleted
with some little changes later)
-----------------------
f(int, int):
mov eax, 0
cmp edi, esi
cmovg eax, edi
ret
-----------------------
