https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114972
Bug ID: 114972
Summary: [11/12/13/14/15 Regression] Missed optimization for
Dead Code Elimination
Product: gcc
Version: 15.0
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 by Dead Code
Elimination, but gcc -O3 missed it.
This is a regression from GCC-6.1.
https://godbolt.org/z/fGzMeba66
int a, b, m;
void func() {
m = a + b;
a++;
b--;
if(a+b-m != 0) m=100; //dead code
}
GCC -O3:
func():
mov eax, DWORD PTR a[rip]
mov edx, DWORD PTR b[rip]
lea ecx, [rax+rdx]
add eax, 1
sub edx, 1
mov DWORD PTR a[rip], eax
add eax, edx
cmp ecx, eax
mov eax, 100
mov DWORD PTR b[rip], edx
cmovne ecx, eax
mov DWORD PTR m[rip], ecx
ret
Expected code (GCC-5.5)
func():
mov edx, DWORD PTR a[rip]
mov eax, DWORD PTR b[rip]
lea ecx, [rdx+rax]
add edx, 1
sub eax, 1
mov DWORD PTR a[rip], edx
mov DWORD PTR b[rip], eax
mov DWORD PTR m[rip], ecx
ret
Thank you very much for your time and effort! We look forward to hearing from
you.
