https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102981
Bug ID: 102981
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);
void bar(void);
static int a;
static short b[2][2][2] = {1};
int main() {
int c = 0;
short d = 0;
for (; d <= 1; d++) {
if (c)
foo();
for (; a < 0; a++) {
bar();
if (!b[d][d][d])
c = 1;
}
}
}
11.2.0 at -O3 can eliminate the call to foo but trunk at -O3 cannot:
gcc-11 test.c -O3 -S -o /dev/stdout
...
main:
.LFB0:
.cfi_startproc
movl a(%rip), %eax
testl %eax, %eax
jns .L6
subq $8, %rsp
.cfi_def_cfa_offset 16
.p2align 4,,10
.p2align 3
.L3:
call bar
addl $1, a(%rip)
js .L3
xorl %eax, %eax
addq $8, %rsp
.cfi_def_cfa_offset 8
ret
.L6:
xorl %eax, %eax
ret
.cfi_endproc
gcc-trunk test.c -O3 -S -o /dev/stdout
main:
.LFB0:
.cfi_startproc
pushq %r12
.cfi_def_cfa_offset 16
.cfi_offset 12, -16
movl $1, %r12d
pushq %rbp
.cfi_def_cfa_offset 24
.cfi_offset 6, -24
movl $b, %ebp
pushq %rbx
.cfi_def_cfa_offset 32
.cfi_offset 3, -32
xorl %ebx, %ebx
.L2:
movl a(%rip), %eax
testl %eax, %eax
jns .L4
.p2align 4,,10
.p2align 3
.L6:
call bar
cmpw $0, 0(%rbp)
cmove %r12d, %ebx
addl $1, a(%rip)
js .L6
.L4:
addq $14, %rbp
cmpq $b+28, %rbp
je .L14
testl %ebx, %ebx
je .L2
call foo
jmp .L2
.p2align 4,,10
.p2align 3
.L14:
popq %rbx
.cfi_def_cfa_offset 24
xorl %eax, %eax
popq %rbp
.cfi_def_cfa_offset 16
popq %r12
.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 20211028 (experimental) (GCC)
It started with
https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=d8edfadfc7a9795b65177a50ce44fd348858e844
