https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105832
Bug ID: 105832
Summary: Dead Code Elimination Regression at -O3 (trunk vs.
12.1.0)
Product: gcc
Version: 13.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: theodort at inf dot ethz.ch
Target Milestone: ---
cat case.c #2
void foo(void);
static struct {
short a;
char b;
} c;
static char d;
int main() {
char g = c.b > 4U ? c.b : c.b << 2;
for (int h = 0; h < 5; h++) {
d = (g >= 2 || 1 >> g) ? g : g << 1;
if (d && 1 == g)
foo();
c.a = 0;
}
}
`gcc-1982fe2692b6c3b7f969ffc4edac59f9d4359e91 (trunk) -O3` can not eliminate
`foo` but `gcc-releases/gcc-12.1.0 -O3` can.
`gcc-1982fe2692b6c3b7f969ffc4edac59f9d4359e91 (trunk) -O3 -S -o /dev/stdout
case.c`
--------- OUTPUT ---------
main:
.LFB0:
.cfi_startproc
movsbl c+2(%rip), %edx
movl %edx, %eax
sall $2, %edx
cmpb $5, %al
cmovb %edx, %eax
cmpb $1, %al
jle .L3
.L13:
xorl %eax, %eax
movw %ax, c(%rip)
xorl %eax, %eax
ret
.L3:
movsbl %al, %edx
addl %edx, %edx
testb %al, %al
cmove %eax, %edx
testb %dl, %dl
je .L13
subb $1, %al
jne .L13
pushq %rbx
.cfi_def_cfa_offset 16
.cfi_offset 3, -16
movl $5, %ebx
.L6:
call foo
movw $0, c(%rip)
subl $1, %ebx
jne .L6
xorl %eax, %eax
popq %rbx
.cfi_def_cfa_offset 8
ret
---------- END OUTPUT ---------
`gcc-releases/gcc-12.1.0 -O3 -S -o /dev/stdout case.c`
--------- OUTPUT ---------
main:
.LFB0:
.cfi_startproc
xorl %eax, %eax
movw %ax, c(%rip)
xorl %eax, %eax
ret
---------- END OUTPUT ---------
Bisects to:
https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=a1c9f779f75283427316b5c670c1e01ff8ce9ced
