https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108352
Bug ID: 108352
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 54227
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=54227&action=edit
Code as file
cat case.c #30
long a;
int b;
void bar64_(void);
void foo();
int main() {
char c = 0;
unsigned d = 10;
int e = 2;
for (; d; d--) {
bar64_();
b = d;
e && (c = (e = 0) != 4) > 1;
}
if (c < 1)
foo();
a = b;
}
`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
pushq %r13
.cfi_def_cfa_offset 16
.cfi_offset 13, -16
movl $1, %r13d
pushq %r12
.cfi_def_cfa_offset 24
.cfi_offset 12, -24
movl $2, %r12d
pushq %rbp
.cfi_def_cfa_offset 32
.cfi_offset 6, -32
xorl %ebp, %ebp
pushq %rbx
.cfi_def_cfa_offset 40
.cfi_offset 3, -40
movl $10, %ebx
subq $8, %rsp
.cfi_def_cfa_offset 48
.p2align 4,,10
.p2align 3
.L3:
call bar64_
testl %r12d, %r12d
movl %ebx, b(%rip)
cmovne %r13d, %ebp
xorl %r12d, %r12d
subl $1, %ebx
jne .L3
movl $1, %eax
testb %bpl, %bpl
je .L10
.L4:
movq %rax, a(%rip)
addq $8, %rsp
.cfi_remember_state
.cfi_def_cfa_offset 40
xorl %eax, %eax
popq %rbx
.cfi_def_cfa_offset 32
popq %rbp
.cfi_def_cfa_offset 24
popq %r12
.cfi_def_cfa_offset 16
popq %r13
.cfi_def_cfa_offset 8
ret
.L10:
.cfi_restore_state
xorl %eax, %eax
call foo
movslq b(%rip), %rax
jmp .L4
---------- END OUTPUT ---------
`gcc-releases/gcc-12.2.0 -O2 -S -o /dev/stdout case.c`
--------- OUTPUT ---------
main:
.LFB0:
.cfi_startproc
pushq %rbx
.cfi_def_cfa_offset 16
.cfi_offset 3, -16
movl $10, %ebx
call bar64_
movl $10, %eax
jmp .L3
.p2align 4,,10
.p2align 3
.L6:
call bar64_
movl %ebx, %eax
.L3:
movl %eax, b(%rip)
subl $1, %ebx
jne .L6
movq $1, a(%rip)
xorl %eax, %eax
popq %rbx
.cfi_def_cfa_offset 8
ret
---------- END OUTPUT ---------
Bisects to:
https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=d86d81a449c03641e079f23a2b3e1b2279a162fe
