https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108357
Bug ID: 108357
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 54232
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=54232&action=edit
presented code as file
cat case.c #411
static char b;
static unsigned c;
void foo();
short(a)(short d, short e) { return d * e; }
static short f(short d) {
b = 0;
if ((d && 0 >= c < d) ^ d)
;
else
foo();
return d;
}
int main() {
short g = a(5, b ^ 9854);
f(g);
}
`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:
.LFB2:
.cfi_startproc
movsbw b(%rip), %ax
movb $0, b(%rip)
xorw $9854, %ax
leal (%rax,%rax,4), %eax
cmpw $1, %ax
movswl %ax, %edx
setg %al
movzbl %al, %eax
cmpl %eax, %edx
je .L9
xorl %eax, %eax
ret
.L9:
pushq %rax
.cfi_def_cfa_offset 16
xorl %eax, %eax
call foo
xorl %eax, %eax
popq %rdx
.cfi_def_cfa_offset 8
ret
---------- END OUTPUT ---------
`gcc-releases/gcc-12.2.0 -O2 -S -o /dev/stdout case.c`
--------- OUTPUT ---------
main:
.LFB2:
.cfi_startproc
movb $0, b(%rip)
xorl %eax, %eax
ret
---------- END OUTPUT ---------
Bisects to:
https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=2dc5d6b1e7ec8822f5bd78761962ca2c85d4a2b4
