https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108355
Bug ID: 108355
Summary: Dead Code Elimination Regression at -O2 (trunk vs.
12.2.0)
Product: gcc
Version: 13.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: yann at ywg dot ch
Target Milestone: ---
Created attachment 54230
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=54230&action=edit
presented code as file
cat case.c #551
int a;
int *b = &a;
int **c = &b;
int d;
void bar25_(void);
void foo(void);
int main() {
int e[][1] = {0, 0, 0, 0, 0, 1};
for (;;) {
bar25_();
if (e[5][a])
break;
e[a][0] = 0;
foo();
}
*c = &d;
}
`gcc-cb93c5f8008b95743b741d6f1842f9be50c6985c (trunk) -O2` can not eliminate
`foo` but `gcc-releases/gcc-12.2.0 -O2` can.
`gcc-cb93c5f8008b95743b741d6f1842f9be50c6985c (trunk) -O2 -S -o /dev/stdout
case.c`
--------- OUTPUT ---------
main:
.LFB0:
.cfi_startproc
subq $40, %rsp
.cfi_def_cfa_offset 48
movl $1, 20(%rsp)
jmp .L3
.p2align 4,,10
.p2align 3
.L6:
movl $0, (%rsp,%rax,4)
call foo
.L3:
call bar25_
movslq a(%rip), %rax
movl 20(%rsp,%rax,4), %edx
testl %edx, %edx
je .L6
movq c(%rip), %rax
movq $d, (%rax)
xorl %eax, %eax
addq $40, %rsp
.cfi_def_cfa_offset 8
ret
---------- END OUTPUT ---------
`gcc-releases/gcc-12.2.0 -O2 -S -o /dev/stdout case.c`
--------- OUTPUT ---------
main:
.LFB0:
.cfi_startproc
subq $8, %rsp
.cfi_def_cfa_offset 16
call bar25_
movq c(%rip), %rax
movq $d, (%rax)
xorl %eax, %eax
addq $8, %rsp
.cfi_def_cfa_offset 8
ret
---------- END OUTPUT ---------
Bisects to:
https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=9baee6181b4e427e0b5ba417e51424c15858dce7
