https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102705
Bug ID: 102705
Summary: [12 Regression] Dead Code Elimination Regression at
-O3 (trunk vs 11.2.0)
Product: gcc
Version: 12.0
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 test.c
void foo(void);
static int b;
static char c;
static short a(short d, short e) { return e == 0 || d && e == 1 ? 0 : d % e; }
int main() {
b = c = b >= 2 ? 0 : 1 >> b;
short f = a(0 >= 0 ^ c, 5);
if (f == c)
foo();
a(0, 9);
}
11.2.0 at -O3 can eliminate the call to foo but trunk at -O3 cannot:
gcc-11.2.0 test.c -S -O3 -o /dev/stdout
main:
.LFB1:
.cfi_startproc
movl b(%rip), %ecx
movl $1, %eax
sarl %cl, %eax
movl %eax, %edx
xorl %eax, %eax
cmpl $2, %ecx
cmovl %edx, %eax
movsbl %al, %eax
movl %eax, b(%rip)
xorl %eax, %eax
ret
.cfi_endproc
gcc-trunk test.c -S -O3 -o /dev/stdout
main:
.LFB1:
.cfi_startproc
movl b(%rip), %ecx
cmpl $1, %ecx
jle .L2
xorl %ecx, %ecx
movl %ecx, b(%rip)
.L5:
xorl %eax, %eax
ret
.L2:
movl $1, %eax
sarl %cl, %eax
movl %eax, %edx
movl %eax, b(%rip)
xorl $1, %edx
movsbw %dl, %dx
cmpw %ax, %dx
jne .L5
pushq %rax
.cfi_def_cfa_offset 16
call foo
xorl %eax, %eax
popq %rdx
.cfi_def_cfa_offset 8
ret
.cfi_endproc
gcc-trunk -v
Using built-in specs.
Target: x86_64-pc-linux-gnu
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 12.0.0 20211012 (experimental) (GCC)
It started with
https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=145bc41dae7c7bfa093d61e77346f98e6a595a0e
