https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114277
Bug ID: 114277
Summary: Missed optimization: x*(x||b) => x
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: 652023330028 at smail dot nju.edu.cn
Target Milestone: ---
Hello, we noticed that the code below can be optimized as stated in the title
(x*(x||b) => x), but gcc -O3 missed it.
https://godbolt.org/z/W8xYrGdej
int a,b;
void func(int x){
a=x*(x||b);
}
GCC -O3:
func(int):
mov eax, edi
or eax, DWORD PTR b[rip]
mov eax, 0
cmove edi, eax
mov DWORD PTR a[rip], edi
ret
Expected code:
func(int):
mov DWORD PTR a[rip], edi
ret
Surprisingly, GCC optimizes as expected for the following slightly more complex
code:
int c;
void func2(int x){
a=x*(x||(b&&c));
}
func2(int):
mov DWORD PTR a[rip], edi
ret
Thank you very much for your time and effort! We look forward to hearing from
you.
