https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107822
Bug ID: 107822
Summary: Dead Code Elimination Regression at -Os (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 53945
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=53945&action=edit
Code
cat case.c #230636
int b;
void foo();
void(a)();
int main() {
int c;
int *d = &c;
*d = a && 8;
b = 0;
for (; b < 9; ++b)
*d ^= 3;
if (*d)
;
else
foo();
}
`gcc-e4faee8d02ec5d65bf418612f7181823eb08c078 (trunk) -Os` can not eliminate
`foo` but `gcc-releases/gcc-12.2.0 -Os` can.
`gcc-e4faee8d02ec5d65bf418612f7181823eb08c078 (trunk) -Os -S -o /dev/stdout
case.c`
--------- OUTPUT ---------
main:
.LFB0:
.cfi_startproc
movl $10, %edx
xorl %ecx, %ecx
movl $1, %eax
.L2:
decl %edx
je .L12
xorl $3, %eax
movb $1, %cl
jmp .L2
.L12:
testb %cl, %cl
jne .L4
xorl %esi, %esi
movl %esi, b(%rip)
jmp .L5
.L4:
movl $9, b(%rip)
.L5:
testl %eax, %eax
jne .L8
pushq %rdx
.cfi_def_cfa_offset 16
call foo
xorl %eax, %eax
popq %rcx
.cfi_def_cfa_offset 8
ret
.L8:
xorl %eax, %eax
ret
---------- END OUTPUT ---------
`gcc-releases/gcc-12.2.0 -Os -S -o /dev/stdout case.c`
--------- OUTPUT ---------
main:
.LFB0:
.cfi_startproc
movl $9, b(%rip)
xorl %eax, %eax
ret
---------- END OUTPUT ---------
Bisects to:
https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=e7310e24b1c0ca67b1bb507c1330b2bf39e59e32
