https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113265
Bug ID: 113265
Summary: [Regression] Missed optimization for redundancy
computation elimination may be due to constant
propagation about 0 too late
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 maybe there is a missed optimization for redundancy
computation elimination.
https://godbolt.org/z/drfejE5cP
int x,y,z;
void func(int a, int b){
a=b-x;
b=a;
y=0;
z=(y+a)/(-b);
}
GCC -O3 :
func(int, int):
mov ecx, DWORD PTR x[rip]
mov eax, esi
mov DWORD PTR y[rip], 0
sub eax, ecx
sub ecx, esi
cdq
idiv ecx
mov DWORD PTR z[rip], eax
ret
Earlier GCC versions get the expected optimizations:
Expected code (GCC 7.5):
func(int, int):
mov DWORD PTR y[rip], 0
mov DWORD PTR z[rip], -1
ret
The following code is optimized by gcc as expected:
void func2(int a, int b){
a=b-x;
b=a;
y=0;
z=(0+a)/(-b);
}
Comparing the code for func and func2 and their ccp1(tree), we suspect that
this issue may be caused by too late propagation about y=0.
Thank you very much for your time and effort! We look forward to hearing from
you
